ORCID Profile
0000-0002-0301-8033
Current Organisation
University of Oxford
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Photonics and Electro-Optical Engineering (excl. Communications) | Nanotechnology | Materials Engineering Not Elsewhere Classified | Optics And Opto-Electronic Physics | Nanotechnology | Optical Physics | Condensed Matter Physics | Photodetectors, Optical Sensors and Solar Cells | Electrical and Electronic Engineering | Nanophotonics | Compound Semiconductors | Interdisciplinary Engineering Not Elsewhere Classified | Materials Engineering | Surfaces and Structural Properties of Condensed Matter | Photonics, Optoelectronics and Optical Communications | Electronic and Magnetic Properties of Condensed Matter; Superconductivity | Condensed Matter Characterisation Technique Development | Nanoelectronics | Nanofabrication, Growth and Self Assembly
ANZSRC Socio-Economic Objective (SEO)
Expanding Knowledge in the Physical Sciences | Expanding Knowledge in Engineering | Physical sciences | Emerging Defence Technologies | Integrated circuits and devices | Scientific instrumentation | Expanding Knowledge in Technology | Other | Solar-Photovoltaic Energy | Health and support services not elsewhere classified |
Related Links
Publications
Characterisation of nanostructures via terahertz spectroscopy
Publisher: IEEE
Date: 12-2010
Growth of Si and C delta-doped nipi doping superlattices in GaAs by metal organic vapor phase epitaxy
Publisher: AIP Publishing
Date: 30-12-1996
DOI: 10.1063/1.116991
Abstract: We have optimized growth conditions of metal organic vapor phase epitaxy (MOVPE) in order to grow Si and C δ-doped nipi doping superlattices in GaAs. Trimethylaluminium (TMAl) and silane (SiH4) were used as p-type and n-type doping precursors, respectively. We report that at 630 °C, full compensation of free electrons and holes can be obtained in the MOVPE-grown Si and C δ-doped nipi doping superlattices over a very wide range of the sheet carrier densities (1012–1013 cm−2) by choosing proper TMAl flow rate and Si δ-doping time or SiH4 flow rate. The experimental results on electrical and optical characterization of Si and C δ-doped nipi doping superlattices in GaAs with 150 Å thick undoped spacer layers are presented.
Proton irradiation-induced intermixing in InGaAs/(Al)GaAs quantum wells and quantum-well lasers
Publisher: AIP Publishing
Date: 05-1999
DOI: 10.1063/1.370291
Abstract: Proton irradiation with subsequent rapid thermal annealing was used to investigate intermixing of InGaAs/GaAs and InGaAs/AlGaAs quantum wells. Large photoluminescence (PL) energy shifts were observed in both materials. Comparatively, InGaAs/AlGaAs s les showed larger PL energy shifts than InGaAs/GaAs s les because of the presence of Al in the barriers and also better recovery of PL intensities, which is mainly due to dynamic annealing effects in AlGaAs during irradiation. Based on this, InGaAs/AlGaAs quantum-well lasers were fabricated and up to 49.3-nm-emission wavelength shift was observed in the proton-irradiated laser with no significant degradation in device characteristics.
Progress on THz applications for Plasma Diagnostics
Publisher: IEEE
Date: 08-2015
Photocurrent Spectroscopy of Perovskite Solar Cells Over a Wide Temperature Range from 15 to 350 K
Publisher: American Chemical Society (ACS)
Date: 29-12-2017
DOI: 10.1021/ACS.JPCLETT.7B02935
Abstract: Solar cells based on metal halide perovskite thin films show great promise for energy generation in a range of environments from terrestrial installations to space applications. Here we assess the device characteristics of the prototypical perovskite solar cells based on methylammonium lead triiodide (CH
Correction to “A Templating Approach to Controlling the Growth of Coevaporated Halide Perovskites”
Publisher: American Chemical Society (ACS)
Date: 18-10-2023
Simulation and optimisation of terahertz emission from InGaAs and InP photoconductive switches
Publisher: Elsevier BV
Date: 12-2005
Compound Semiconductors for Terahertz Photonics
Publisher: IEEE
Date: 10-2007
Efficient generation of charges via below-gap photoexcitation of polymer-fullerene blend films investigated by terahertz spectroscopy
Publisher: American Physical Society (APS)
Date: 24-09-2008
Temperature‐Dependent Charge‐Carrier Dynamics in CH3NH3PbI3 Perovskite Thin Films
Publisher: Wiley
Date: 15-09-2015
Enhanced Amplified Spontaneous Emission in Perovskites Using a Flexible Cholesteric Liquid Crystal Reflector
Publisher: American Chemical Society (ACS)
Date: 08-07-2015
DOI: 10.1021/ACS.NANOLETT.5B00678
Abstract: Organic-inorganic perovskites are highly promising solar cell materials with laboratory-based power conversion efficiencies already matching those of established thin film technologies. Their exceptional photovoltaic performance is in part attributed to the presence of efficient radiative recombination pathways, thereby opening up the possibility of efficient light-emitting devices. Here, we demonstrate optically pumped lified spontaneous emission (ASE) at 780 nm from a 50 nm-thick film of CH3NH3PbI3 perovskite that is sandwiched within a cavity composed of a thin-film (∼7 μm) cholesteric liquid crystal (CLC) reflector and a metal back-reflector. The threshold fluence for ASE in the perovskite film is reduced by at least two orders of magnitude in the presence of the CLC reflector, which results in a factor of two reduction in threshold fluence compared to previous reports. We consider this to be due to improved coupling of the oblique and out-of-plane modes that are reflected into the bulk in addition to any contributions from cavity modes. Furthermore, we also demonstrate enhanced ASE on flexible reflectors and discuss how improvements in the quality factor and reflectivity of the CLC layers could lead to single-mode lasing using CLC reflectors. Our work opens up the possibility of fabricating widely wavelength-tunable "mirror-less" single-mode lasers on flexible substrates, which could find use in applications such as flexible displays and friend or foe identification.
Engineering III-V nanowires for optoelectronics: from epitaxy to terahertz photonics
Publisher: SPIE
Date: 21-02-2018
DOI: 10.1117/12.2299831
An Ultrafast Semiconducting Nanowire THz Polarization Modulator
Publisher: IEEE
Date: 09-2019
Efficient and Air‐Stable Mixed‐Cation Lead Mixed‐Halide Perovskite Solar Cells with n‐Doped Organic Electron Extraction Layers
Publisher: Wiley
Date: 12-2016
Abstract: Air-stable doping of the n-type fullerene layer in an n-i-p planar heterojunction perovskite device is capable of enhancing device efficiency and improving device stability. Employing a (HC(NH
Optical properties and limiting photocurrent of thin-film perovskite solar cells
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4EE03224A
Abstract: Thorough measurements of the optical constants of CH 3 NH 3 PbI 3 are used to determine the limiting parasitic losses in solar cells revealing up to 100% IQE and excellent performance at oblique incidence.
Nanoengineering Coaxial Carbon Nanotube–Dual-Polymer Heterostructures
Publisher: American Chemical Society (ACS)
Date: 20-06-2012
DOI: 10.1021/NN301133V
Abstract: We describe studies of new nanostructured materials consisting of carbon nanotubes wrapped in sequential coatings of two different semiconducting polymers, namely, poly(3-hexylthiophene) (P3HT) and poly(9,9'-dioctylfluorene-co-benzothiadiazole) (F8BT). Using absorption spectroscopy and steady-state and ultrafast photoluminescence measurements, we demonstrate the role of the different layer structures in controlling energy levels and charge transfer in both solution and film s les. By varying the simple solution processing steps, we can control the ordering and proportions of the wrapping polymers in the solid state. The resulting novel coaxial structures open up a variety of new applications for nanotube blends and are particularly promising for implementation into organic photovoltaic devices. The carbon nanotube template can also be used to optimize both the electronic properties and morphology of polymer composites in a much more controlled fashion than achieved previously, offering a route to producing a new generation of polymer nanostructures.
Influence of surface passivation on ultrafast carrier dynamics and terahertz radiation generation in GaAs
Publisher: AIP Publishing
Date: 04-12-2006
DOI: 10.1063/1.2398915
Abstract: The carrier dynamics of photoexcited electrons in the vicinity of the surface of (NH4)2S-passivated GaAs were studied via terahertz emission spectroscopy and optical-pump terahertz-probe spectroscopy. Terahertz emission spectroscopy measurements, coupled with Monte Carlo simulations of terahertz emission, revealed that the surface electric field of GaAs reverses after passivation. The conductivity of photoexcited electrons was determined via optical-pump terahertz-probe spectroscopy and was found to double after passivation. These experiments demonstrate that passivation significantly reduces the surface state density and surface recombination velocity of GaAs. Finally, it was demonstrated that passivation leads to an enhancement in the power radiated by photoconductive switch terahertz emitters, thereby showing the important influence of surface chemistry on the performance of ultrafast terahertz photonic devices.
Charge-Carrier Dynamics in 2D Hybrid Metal–Halide Perovskites
Publisher: American Chemical Society (ACS)
Date: 06-10-2016
DOI: 10.1021/ACS.NANOLETT.6B03114
Abstract: Hybrid metal-halide perovskites are promising new materials for use in solar cells however, their chemical stability in the presence of moisture remains a significant drawback. Quasi two-dimensional (2D) perovskites that incorporate hydrophobic organic interlayers offer improved resistance to degradation by moisture, currently still at the cost of overall cell efficiency. To elucidate the factors affecting the optoelectronic properties of these materials, we have investigated the charge transport properties and crystallographic orientation of mixed methylammonium (MA)-phenylethylammonium (PEA) lead iodide thin films as a function of the MA-to-PEA ratio and, thus, the thickness of the "encapsulated" MA lead-halide layers. We find that monomolecular charge-carrier recombination rates first decrease with increasing PEA fraction, most likely as a result of trap passivation, but then increase significantly as excitonic effects begin to dominate for thin confined layers. Bimolecular and Auger recombination rate constants are found to be sensitive to changes in electronic confinement, which alters the density of states for electronic transitions. We demonstrate that effective charge-carrier mobilities remain remarkably high (near 10 cm
Extreme sensitivity of graphene photoconductivity to environmental gases
Publisher: Springer Science and Business Media LLC
Date: 27-11-2012
DOI: 10.1038/NCOMMS2235
The Effects of Doping Density and Temperature on the Optoelectronic Properties of Formamidinium Tin Triiodide Thin Films
Publisher: Wiley
Date: 17-09-2018
Abstract: Optoelectronic properties are unraveled for formamidinium tin triiodide (FASnI
An ion-implanted InP receiver for polarization resolved terahertz spectroscopy
Publisher: The Optical Society
Date: 2007
DOI: 10.1364/OE.15.007047
Abstract: We report on the construction, optical alignment and performance of a receiver which is capable of recording the full polarization state of coherent terahertz radiation. The photoconductive detector was fabricated on InP which had been implanted with Fe(+) ions. The device operated successfully when it was gated with near infrared femtosecond pulses from either a Ti:sapphire laser oscillator or a 1 kHz regenerative laser lifier. When illuminated with terahertz radiation from a typical photoconductive source, the optimized device had a signal to noise figure of 100:1 with a usable spectral bandwidth of up to 4 THz. The device was shown to be very sensitive to terahertz polarization, being able to resolve changes in polarization of 0.34 degrees. Additionally, we have demonstrated the usefulness of this device for (i) polarization sensitive terahertz spectroscopy, by measuring the birefringence of quartz and (ii) terahertz emission experiments, by measuring the polarization dependence of radiation generated by optical rectification in (110)-ZnTe.
Elucidating the long-range charge carrier mobility in metal halide perovskite thin films
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C8EE03395A
Abstract: A new optoelectronic technique which enables the accurate determination of the long-range lateral charge carrier mobility of metal halide perovskite films.
Carrier Lifetime and Mobility Enhancement in Nearly Defect-Free Core−Shell Nanowires Measured Using Time-Resolved Terahertz Spectroscopy
Publisher: American Chemical Society (ACS)
Date: 28-07-2009
DOI: 10.1021/NL9016336
Abstract: We have used transient terahertz photoconductivity measurements to assess the efficacy of two-temperature growth and core-shell encapsulation techniques on the electronic properties of GaAs nanowires. We demonstrate that two-temperature growth of the GaAs core leads to an almost doubling in charge-carrier mobility and a tripling of carrier lifetime. In addition, overcoating the GaAs core with a larger-bandgap material is shown to reduce the density of surface traps by 82%, thereby enhancing the charge conductivity.
Low ensemble disorder in quantum well tube nanowires
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5NR06996C
Abstract: Single core–multishell nanowires with a radial quantum well are probed by micro-photoluminescence spectroscopy revealing low disorder in both the core and quantum well.
Publisher Correction: High irradiance performance of metal halide perovskites for concentrator photovoltaics
Publisher: Springer Science and Business Media LLC
Date: 13-08-2018
Band‐Tail Recombination in Hybrid Lead Iodide Perovskite
Publisher: Wiley
Date: 05-06-2017
Carrier dynamics in ion-implanted GaAs studied by simulation and observation of terahertz emission
Publisher: American Physical Society (APS)
Date: 12-2004
Optoelectronics: Colour-selective photodiodes
Publisher: Springer Science and Business Media LLC
Date: 29-09-2015
The 2017 terahertz science and technology roadmap
Publisher: IOP Publishing
Date: 04-01-2017
An ultrafast carbon nanotube terahertz polarisation modulator
Publisher: AIP Publishing
Date: 28-05-2014
DOI: 10.1063/1.4879895
Abstract: We demonstrate ultrafast modulation of terahertz radiation by unaligned optically pumped single-walled carbon nanotubes. Photoexcitation by an ultrafast optical pump pulse induces transient terahertz absorption in nanowires aligned parallel to the optical pump. By controlling the polarisation of the optical pump, we show that terahertz polarisation and modulation can be tuned, allowing sub-picosecond modulation of terahertz radiation. Such speeds suggest potential for semiconductor nanowire devices in terahertz communication technologies.
Near‐Infrared and Short‐Wavelength Infrared Photodiodes Based on Dye–Perovskite Composites
Publisher: Wiley
Date: 04-08-2017
Charge‐Carrier Trapping and Radiative Recombination in Metal Halide Perovskite Semiconductors
Publisher: Wiley
Date: 20-08-2020
Engineering III–V Nanowires for Optoelectronics: From Visible to Terahertz
Publisher: OSA
Date: 2019
Radiative Monomolecular Recombination Boosts Amplified Spontaneous Emission in HC(NH2)2SnI3 Perovskite Films
Publisher: American Chemical Society (ACS)
Date: 07-10-2016
DOI: 10.1021/ACS.JPCLETT.6B02030
Abstract: Hybrid metal-halide perovskites have potential as cost-effective gain media for laser technology because of their superior optoelectronic properties. Although lead-halide perovskites have been most widely studied to date, tin-based perovskites have been proposed as a less toxic alternative. In this Letter, we show that lified spontaneous emission (ASE) in formamidinium tin triiodide (FASnI
An Ultrafast Switchable Terahertz Polarization Modulator Based on III-V Semiconductor Nanowires
Publisher: American Chemical Society (ACS)
Date: 30-03-2017
DOI: 10.1021/ACS.NANOLETT.7B00401
Abstract: Progress in the terahertz (THz) region of the electromagnetic spectrum is undergoing major advances, with advanced THz sources and detectors being developed at a rapid pace. Yet, ultrafast THz communication is still to be realized, owing to the lack of practical and effective THz modulators. Here, we present a novel ultrafast active THz polarization modulator based on GaAs semiconductor nanowires arranged in a wire-grid configuration. We utilize an optical pump-terahertz probe spectroscopy system and vary the polarization of the optical pump beam to demonstrate ultrafast THz modulation with a switching time of less than 5 ps and a modulation depth of -8 dB. We achieve an extinction of over 13% and a dynamic range of -9 dB, comparable to microsecond-switchable graphene- and metamaterial-based THz modulators, and surpassing the performance of optically switchable carbon nanotube THz polarizers. We show a broad bandwidth for THz modulation between 0.1 and 4 THz. Thus, this work presents the first THz modulator which combines not only a large modulation depth but also a broad bandwidth and picosecond time resolution for THz intensity and phase modulation, making it an ideal candidate for ultrafast THz communication.
Effect of Structural Phase Transition on Charge-Carrier Lifetimes and Defects in CH3NH3SnI3 Perovskite
Publisher: American Chemical Society (ACS)
Date: 23-03-2016
DOI: 10.1021/ACS.JPCLETT.6B00322
Abstract: Methylammonium tin triiodide (MASnI3) has been successfully employed in lead-free perovskite solar cells, but overall power-conversion efficiencies are still significantly lower than for lead-based perovskites. Here we present photoluminescence (PL) spectra and time-resolved PL from 8 to 295 K and find a marked improvement in carrier lifetime and a substantial reduction in PL line width below ∼110 K, indicating that the cause of the hindered performance is activated at the orthorhombic to tetragonal phase transition. Our measurements therefore suggest that targeted structural change may be capable of tailoring the relative energy level alignment of defects (e.g., tin vacancies) to reduce the background dopant density and improve charge extraction. In addition, we observe for the first time an above-gap emission feature that may arise from higher-lying interband transitions, raising the prospect of excess energy harvesting.
Conductivity of nanoporous InP membranes investigated using terahertz spectroscopy
Publisher: IEEE
Date: 11-2008
Broadband Phase-Sensitive Single InP Nanowire Photoconductive Terahertz Detectors
Publisher: American Chemical Society (ACS)
Date: 18-07-2016
DOI: 10.1021/ACS.NANOLETT.6B01528
Abstract: Terahertz time-domain spectroscopy (THz-TDS) has emerged as a powerful tool for materials characterization and imaging. A trend toward size reduction, higher component integration, and performance improvement for advanced THz-TDS systems is of increasing interest. The use of single semiconducting nanowires for terahertz (THz) detection is a nascent field that has great potential to realize future highly integrated THz systems. In order to develop such components, optimized material optoelectronic properties and careful device design are necessary. Here, we present antenna-optimized photoconductive detectors based on single InP nanowires with superior properties of high carrier mobility (∼1260 cm(2) V(-1) s(-1)) and low dark current (∼10 pA), which exhibit excellent sensitivity and broadband performance. We demonstrate that these nanowire THz detectors can provide high quality time-domain spectra for materials characterization in a THz-TDS system, a critical step toward future application in advanced THz-TDS system with high spectral and spatial resolution.
Terahertz Properties of Graphene
Publisher: Springer Science and Business Media LLC
Date: 09-06-2012
Bimolecular recombination in methylammonium lead triiodide perovskite is an inverse absorption process
Publisher: Springer Science and Business Media LLC
Date: 18-01-2018
DOI: 10.1038/S41467-017-02670-2
Abstract: Photovoltaic devices based on metal halide perovskites are rapidly improving in efficiency. Once the Shockley–Queisser limit is reached, charge-carrier extraction will be limited only by radiative bimolecular recombination of electrons with holes. Yet, this fundamental process, and its link with material stoichiometry, is still poorly understood. Here we show that bimolecular charge-carrier recombination in methylammonium lead triiodide perovskite can be fully explained as the inverse process of absorption. By correctly accounting for contributions to the absorption from excitons and electron-hole continuum states, we are able to utilise the van Roosbroeck–Shockley relation to determine bimolecular recombination rate constants from absorption spectra. We show that the sharpening of photon, electron and hole distribution functions significantly enhances bimolecular charge recombination as the temperature is lowered, mirroring trends in transient spectroscopy. Our findings provide vital understanding of band-to-band recombination processes in this hybrid perovskite, which comprise direct, fully radiative transitions between thermalized electrons and holes.
Introduction to the special issue on photoconductive emission and detection of terahertz radiation
Publisher: Springer Science and Business Media LLC
Date: 16-03-2012
Perovskite-perovskite tandem photovoltaics with optimized band gaps
Publisher: American Association for the Advancement of Science (AAAS)
Date: 18-11-2016
Abstract: The ready processability of organic-inorganic perovskite materials for solar cells should enable the fabrication of tandem solar cells, in which the top layer is tuned to absorb shorter wavelengths and the lower layer to absorb the remaining longer-wavelength light. The difficulty in making an all-perovskite cell is finding a material that absorbs the red end of the spectrum. Eperon et al. developed an infrared-absorbing mixed tin-lead material that can deliver 14.8% efficiency on its own and 20.3% efficiency in a four-terminal tandem cell. Science , this issue p. 861
Structured Organic–Inorganic Perovskite toward a Distributed Feedback Laser
Publisher: Wiley
Date: 02-12-2015
Abstract: A general strategy for the in-plane structuring of organic-inorganic perovskite films is presented. The method is used to fabricate an industrially relevant distributed feedback (DFB) cavity, which is a critical step toward all-electrially pumped injection laser diodes. This approach opens the prospects of perovskite materials for much improved optical control in LEDs, solar cells, and also toward applications as optical devices.
Hybrid Perovskites for Photovoltaics: Charge-Carrier Recombination, Diffusion, and Radiative Efficiencies
Publisher: American Chemical Society (ACS)
Date: 10-12-2015
DOI: 10.1021/ACS.ACCOUNTS.5B00411
Abstract: Photovoltaic (PV) devices that harvest the energy provided by the sun have great potential as renewable energy sources, yet uptake has been h ered by the increased cost of solar electricity compared with fossil fuels. Hybrid metal halide perovskites have recently emerged as low-cost active materials in PV cells with power conversion efficiencies now exceeding 20%. Rapid progress has been achieved over only a few years through improvements in materials processing and device design. In addition, hybrid perovskites appear to be good light emitters under certain conditions, raising the prospect of applications in low-cost light-emitting diodes and lasers. Further optimization of such hybrid perovskite devices now needs to be supported by a better understanding of how light is converted into electrical currents and vice versa. This Account provides an overview of charge-carrier recombination and mobility mechanisms encountered in such materials. Optical-pump-terahertz-probe (OPTP) photoconductivity spectroscopy is an ideal tool here, because it allows the dynamics of mobile charge carriers inside the perovskite to be monitored following excitation with a short laser pulse whose photon energy falls into the range of the solar spectrum. We first review our insights gained from transient OPTP and photoluminescence spectroscopy on the mechanisms dominating charge-carrier recombination in these materials. We discuss that mono-molecular charge-recombination predominantly originates from trapping of charges, with trap depths being relatively shallow (tens of millielectronvolts) for hybrid lead iodide perovskites. Bimolecular recombination arises from direct band-to-band electron-hole recombination and is found to be in significant violation of the simple Langevin model. Auger recombination exhibits links with electronic band structure, in accordance with its requirement for energy and momentum conservation for all charges involved. We further discuss charge-carrier mobility values extracted from OPTP measurements and their dependence on perovskite composition and morphology. The significance of the reviewed charge-carrier recombination and mobility parameters is subsequently evaluated in terms of the charge-carrier diffusion lengths and radiative efficiencies that may be obtained for such hybrid perovskites. We particularly focus on calculating such quantities in the limit of ultra-low trap-related recombination, which has not yet been demonstrated but could be reached through further advances in material processing. We find that for thin films of hybrid lead iodide perovskites with typical charge-carrier mobilities of ∼30cm(2)/(V s), charge-carrier diffusion lengths at solar (AM1.5) irradiation are unlikely to exceed ∼10 μm even if all trap-related recombination is eliminated. We further examine the radiative efficiency for hybrid lead halide perovskite films and show that if high efficiencies are to be obtained for intermediate charge-carrier densities (n ≈ 10(14) cm(-3)) trap-related recombination lifetimes will have to be enhanced well into the microsecond range.
Improved carrier collection in intermixed InGaAs/GaAs quantum wells
Publisher: AIP Publishing
Date: 07-12-1998
DOI: 10.1063/1.122780
Abstract: We have used photoluminescence up conversion to study the carrier capture times into intermixed InGaAs/GaAs quantum wells. We have found that the capture into the intermixed wells is markedly faster than capture into the reference (unintermixed) quantum wells. The reasons for the significant reduction in the capture time is related to the shape of the intermixed quantum well. Such a reduction in the capture time is beneficial both in terms of the quantum efficiency and the frequency response of intermixed optoelectronic devices.
Charge‐Carrier Dynamics and Mobilities in Formamidinium Lead Mixed‐Halide Perovskites
Publisher: Wiley
Date: 24-09-2015
Abstract: The mixed-halide perovskite FAPb(Bry I1-y )3 is attractive for color-tunable and tandem solar cells. Bimolecular and Auger charge-carrier recombination rate constants strongly correlate with the Br content, y, suggesting a link with electronic structure. FAPbBr3 and FAPbI3 exhibit charge-carrier mobilities of 14 and 27 cm(2) V(-1) s(-1) and diffusion lengths exceeding 1 μm, while mobilities across the mixed Br/I system depend on crystalline phase disorder.
Charge-Carrier Mobility and Localization in Semiconducting Cu2AgBiI6 for Photovoltaic Applications
Publisher: American Chemical Society (ACS)
Date: 07-04-2021
Terahertz conductivity of magnetoexcitons and electrons in semiconductor nanostructures
Publisher: SPIE
Date: 12-02-2009
DOI: 10.1117/12.807546
Electron Mobility and Injection Dynamics in Mesoporous ZnO, SnO2, and TiO2 Films Used in Dye-Sensitized Solar Cells
Publisher: American Chemical Society (ACS)
Date: 26-05-2011
DOI: 10.1021/NN201243Y
Abstract: High-performance dye-sensitized solar cells are usually fabricated using nanostructured TiO(2) as a thin-film electron-collecting material. However, alternative metal-oxides are currently being explored that may offer advantages through ease of processing, higher electron mobility, or interface band energetics. We present here a comparative study of electron mobility and injection dynamics in thin films of TiO(2), ZnO, and SnO(2) nanoparticles sensitized with Z907 ruthenium dye. Using time-resolved terahertz photoconductivity measurements, we show that, for ZnO and SnO(2) nanoporous films, electron injection from the sensitizer has substantial slow components lasting over tens to hundreds of picoseconds, while for TiO(2), the process is predominantly concluded within a few picoseconds. These results correlate well with the overall electron injection efficiencies we determine from photovoltaic cells fabricated from identical nanoporous films, suggesting that such slow components limit the overall photocurrent generated by the solar cell. We conclude that these injection dynamics are not substantially influenced by bulk energy level offsets but rather by the local environment of the dye-nanoparticle interface that is governed by dye binding modes and densities of states available for injection, both of which may vary from site to site. In addition, we have extracted the electron mobility in the three nanoporous metal-oxide films at early time after excitation from terahertz conductivity measurements and compared these with the time-averaged, long-range mobility determined for devices based on identical films. Comparison with established values for single-crystal Hall mobilities of the three materials shows that, while electron mobility values for nanoporous TiO(2) films are approaching theoretical maximum values, both early time, short distance and interparticle electron mobility in nanoporous ZnO or SnO(2) films offer considerable scope for improvement.
Three-dimensional carrier-dynamics simulation of terahertz emission from photoconductive switches
Publisher: American Physical Society (APS)
Date: 02-05-2005
Fast Charge-Carrier Trapping in TiO2 Nanotubes
Publisher: American Chemical Society (ACS)
Date: 21-04-2015
A review of the electrical properties of semiconductor nanowires: insights gained from terahertz conductivity spectroscopy
Publisher: IOP Publishing
Date: 15-09-2016
Exciton dissociation in polymer field-effect transistors studied using terahertz spectroscopy
Publisher: American Physical Society (APS)
Date: 07-03-2008
Impurity Tracking Enables Enhanced Control and Reproducibility of Hybrid Perovskite Vapor Deposition
Publisher: American Chemical Society (ACS)
Date: 17-07-2019
Photovoltaic Performance of FAPbI3 Perovskite Is Hampered by Intrinsic Quantum Confinement
Publisher: American Chemical Society (ACS)
Date: 10-05-2023
Terahertz magnetoconductivity of excitons and electrons in quantum cascade structures
Publisher: American Physical Society (APS)
Date: 18-03-2008
The Route to Nanoscale Terahertz Technology: Nanowire-based Terahertz Detectors and Terahertz Modulators
Publisher: IEEE
Date: 09-2018
Photon Reabsorption Masks Intrinsic Bimolecular Charge-Carrier Recombination in CH3NH3PbI3 Perovskite
Publisher: American Chemical Society (ACS)
Date: 14-03-2027
DOI: 10.1021/ACS.NANOLETT.7B02834
Abstract: An understanding of charge-carrier recombination processes is essential for the development of hybrid metal halide perovskites for photovoltaic applications. We show that typical measurements of the radiative bimolecular recombination constant in CH
Simulation of fluence-dependent photocurrent in terahertz photoconductive receivers
Publisher: IOP Publishing
Date: 26-09-2012
Solution Deposition‐Conversion for Planar Heterojunction Mixed Halide Perovskite Solar Cells
Publisher: Wiley
Date: 30-05-2014
Terahertz radiation from multiplexed photo-dember currents
Publisher: OSA
Date: 2010
DOI: 10.1364/UP.2010.TUB5
Charge-Carrier Trapping Dynamics in Bismuth-Doped Thin Films of MAPbBr3 Perovskite
Publisher: American Chemical Society (ACS)
Date: 17-04-2020
Open-circuit and short-circuit loss management in wide-gap perovskite p-i-n solar cells
Publisher: Springer Science and Business Media LLC
Date: 20-02-2023
DOI: 10.1038/S41467-023-36141-8
Abstract: In this work, we couple theoretical and experimental approaches to understand and reduce the losses of wide bandgap Br-rich perovskite pin devices at open-circuit voltage (V OC ) and short-circuit current (J SC ) conditions. A mismatch between the internal quasi-Fermi level splitting (QFLS) and the external V OC is detrimental for these devices. We demonstrate that modifying the perovskite top-surface with guanidinium-Br and imidazolium-Br forms a low-dimensional perovskite phase at the n -interface, suppressing the QFLS-V OC mismatch, and boosting the V OC . Concurrently, the use of an ionic interlayer or a self-assembled monolayer at the p -interface reduces the inferred field screening induced by mobile ions at J SC , promoting charge extraction and raising the J SC . The combination of the n- and p- type optimizations allows us to approach the thermodynamic potential of the perovskite absorber layer, resulting in 1 cm 2 devices with performance parameters of V OC s up to 1.29 V, fill factors above 80% and J SC s up to 17 mA/cm 2 , in addition to a thermal stability T 80 lifetime of more than 3500 h at 85 °C.
All-Optical Full-Color Displays Using Polymer Nanofibers
Publisher: American Chemical Society (ACS)
Date: 09-02-2011
DOI: 10.1021/NN1034185
Abstract: We report a number of crossed nanofiber structures for full-color micro/nanodisplays, which were formed by assembling flexible poly(trimethylene terephthalate) (PTT) nanofibers under an optical microscope with the assistance of micromanipulators. The color pixels of the displays consist of micro/nanometer sized color spots in a radius of 300-1500 nm, which were realized through crossed junctions of the PTT nanofibers. The colors of the spots were tuned by changing the power ratios of the launched red, green, and blue lights. We further present a new way to develop white light illumination by combination of red, green, and blue lights with assembly techniques and low production costs.
Photoconductive response correction for detectors of terahertz radiation
Publisher: AIP Publishing
Date: 09-2008
DOI: 10.1063/1.2969035
Abstract: Photoconductive detectors are convenient devices for detecting pulsed terahertz radiation. We have optimized Fe+ ion-damaged InP materials for photoconductive detector signal to noise performance using dual-energy doses in the range from 2.5×1012 to 1.0×1016 cm−2. Ion implantation allowed the production of semiconducting materials with free-carrier lifetimes between 0.5 and 2.1 ps, which were measured by optical pump terahertz probe spectroscopy. The time resolved photoconductivity of the detector substrates was acquired as a function of time after excitation by 2 nJ pulses from a laser oscillator. These data, when combined with a deconvolution algorithm, provide an excellent spectral response correction to the raw photocurrent signal recorded by the photoconductive detectors.
Understanding Dark Current-Voltage Characteristics in Metal-Halide Perovskite Single Crystals
Publisher: American Physical Society (APS)
Date: 06-01-2021
Si and C delta-doping of GaAs grown by metal organic vapour phase epitaxy for fabrication of nipi doping superlattices
Publisher: Elsevier BV
Date: 02-1998
Intrinsic quantum confinement in formamidinium lead triiodide perovskite
Publisher: Springer Science and Business Media LLC
Date: 24-08-2020
Single n+-i-n+InP nanowires for highly sensitive terahertz detection
Publisher: IOP Publishing
Date: 20-02-2017
Abstract: Developing single-nanowire terahertz (THz) electronics and employing them as sub-wavelength components for highly-integrated THz time-domain spectroscopy (THz-TDS) applications is a promising approach to achieve future low-cost, highly integrable and high-resolution THz tools, which are desirable in many areas spanning from security, industry, environmental monitoring and medical diagnostics to fundamental science. In this work, we present the design and growth of n
Lead-free organic–inorganic tin halide perovskites for photovoltaic applications
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4EE01076K
Abstract: Perovskite solar cells based on abundant low cost materials promise to compete on performance with mainstream PV. Here we demonstrate lead-free perovskite solar cells, removing a potential barrier to widespread deployment.
Time-resolved THz spectroscopy of metal-halide perovskite single crystals and polycrystalline thin films
Publisher: IEEE
Date: 09-2019
Semiconductor nanowires in terahertz photonics: From spectroscopy to ultrafast nanowire-based devices
Publisher: IEEE
Date: 09-2017
Measuring the electrical properties of semiconductor nanowires using terahertz conductivity spectroscopy
Publisher: SPIE
Date: 07-12-2013
DOI: 10.1117/12.2049016
Efficient, Semitransparent Neutral-Colored Solar Cells Based on Microstructured Formamidinium Lead Trihalide Perovskite
Publisher: American Chemical Society (ACS)
Date: 18-12-2014
DOI: 10.1021/JZ502367K
Abstract: Efficient, neutral-colored semitransparent solar cells are of commercial interest for incorporation into the windows and surfaces of buildings and automobiles. Here, we report on semitransparent perovskite solar cells that are both efficient and neutral-colored, even in full working devices. Using the microstructured architecture previously developed, we achieve higher efficiencies by replacing methylammonium lead iodide perovskite with formamidinium lead iodide. Current-voltage hysteresis is also much reduced. Furthermore, we apply a novel transparent cathode to the devices, enabling us to fabricate neutral-colored semitransparent full solar cells for the first time. Such devices demonstrate over 5% power conversion efficiency for average visible transparencies of almost 30%, retaining impressive color-neutrality. This makes these devices the best-performing single-junction neutral-colored semitransparent solar cells to date. These microstructured perovskite solar cells are shown to have a significant advantage over silicon solar cells in terms of performance at high incident angles of sunlight, making them ideal for building integration.
Excitation-density-dependent generation of broadband terahertz radiation in an asymmetrically excited photoconductive antenna
Publisher: Optica Publishing Group
Date: 02-08-2007
DOI: 10.1364/OL.32.002297
Abstract: The generation of terahertz (THz) transients in photoconductive emitters has been studied by varying the spatial extent and density of the optically excited photocarriers in asymmetrically excited, biased low-temperature-grown GaAs antenna structures. We find a pronounced dependence of the THz pulse intensity and broadband (>6.0 THz) spectral distribution on the pump excitation density and simulate this with a three-dimensional carrier dynamics model. We attribute the observed variation in THz emission to changes in the strength of the screening field.
Investigations of doping via optical pump terahertz-probe spectroscopy
Publisher: IEEE
Date: 08-2017
Charge trapping in polymer transistors probed by terahertz spectroscopy and scanning probe potentiometry
Publisher: AIP Publishing
Date: 11-09-2006
DOI: 10.1063/1.2340057
Abstract: Terahertz time-domain spectroscopy and scanning probe potentiometry were used to investigate charge trapping in polymer field-effect transistors fabricated on a silicon gate. The hole density in the transistor channel was determined from the reduction in the transmitted terahertz radiation under an applied gate voltage. Prolonged device operation creates an exponential decay in the differential terahertz transmission, compatible with an increase in the density of trapped holes in the polymer channel. Taken in combination with scanning probe potentionmetry measurements, these results indicate that device degradation is largely a consequence of hole trapping, rather than of changes to the mobility of free holes in the polymer.
Broadband terahertz emission from ion-implanted semiconductors
Publisher: Springer Berlin Heidelberg
Date: 2006
The role of ultrafast torsional relaxation in the emission from polythiophene aggregates
Publisher: IEEE
Date: 12-2010
Probing the critical electronic properties of III-V nanowires using optical pump-terahertz probe spectroscopy
Publisher: IEEE
Date: 09-2013
Highly Efficient Perovskite Solar Cells with Tunable Structural Color
Publisher: American Chemical Society (ACS)
Date: 13-02-2015
DOI: 10.1021/NL504349Z
THz emitters and detectors based on ion implanted III-V semiconductors
Publisher: IEEE
Date: 09-2006
Nanotechnology for catalysis and solar energy conversion
Publisher: IOP Publishing
Date: 05-11-2020
Abstract: This roadmap on Nanotechnology for Catalysis and Solar Energy Conversion focuses on the application of nanotechnology in addressing the current challenges of energy conversion: ‘high efficiency, stability, safety, and the potential for low-cost/scalable manufacturing’ to quote from the contributed article by Nathan Lewis. This roadmap focuses on solar-to-fuel conversion, solar water splitting, solar photovoltaics and bio-catalysis. It includes dye-sensitized solar cells (DSSCs), perovskite solar cells, and organic photovoltaics. Smart engineering of colloidal quantum materials and nanostructured electrodes will improve solar-to-fuel conversion efficiency, as described in the articles by Waiskopf and Banin and Meyer. Semiconductor nanoparticles will also improve solar energy conversion efficiency, as discussed by Boschloo et al in their article on DSSCs. Perovskite solar cells have advanced rapidly in recent years, including new ideas on 2D and 3D hybrid halide perovskites, as described by Spanopoulos et al ‘Next generation’ solar cells using multiple exciton generation (MEG) from hot carriers, described in the article by Nozik and Beard, could lead to remarkable improvement in photovoltaic efficiency by using quantization effects in semiconductor nanostructures (quantum dots, wires or wells). These challenges will not be met without simultaneous improvement in nanoscale characterization methods. Terahertz spectroscopy, discussed in the article by Milot et al is one ex le of a method that is overcoming the difficulties associated with nanoscale materials characterization by avoiding electrical contacts to nanoparticles, allowing characterization during device operation, and enabling characterization of a single nanoparticle. Besides experimental advances, computational science is also meeting the challenges of nanomaterials synthesis. The article by Kohlstedt and Schatz discusses the computational frameworks being used to predict structure–property relationships in materials and devices, including machine learning methods, with an emphasis on organic photovoltaics. The contribution by Megarity and Armstrong presents the ‘electrochemical leaf’ for improvements in electrochemistry and beyond. In addition, biohybrid approaches can take advantage of efficient and specific enzyme catalysts. These articles present the nanoscience and technology at the forefront of renewable energy development that will have significant benefits to society.
A Templating Approach to Controlling the Growth of Coevaporated Halide Perovskites
Publisher: American Chemical Society (ACS)
Date: 09-2023
Temperature‐Dependent Reversal of Phase Segregation in Mixed‐Halide Perovskites
Publisher: Wiley
Date: 24-03-2023
Abstract: Understanding the mechanism of light‐induced halide segregation in mixed‐halide perovskites is essential for their application in multijunction solar cells. Here, photoluminescence spectroscopy is used to uncover how both increases in temperature and light intensity can counteract the halide segregation process. It is observed that, with increasing temperature, halide segregation in CH 3 NH 3 Pb(Br 0.4 I 0.6 ) 3 first accelerates toward ≈290 K, before slowing down again toward higher temperatures. Such reversal is attributed to the trade‐off between the temperature activation of segregation, for ex le through enhanced ionic migration, and its inhibition by entropic factors. High light intensities meanwhile can also reverse halide segregation however, this is found to be only a transient process that abates on the time scale of minutes. Overall, these observations pave the way for a more complete model of halide segregation and aid the development of highly efficient and stable perovskite multijunction and concentrator photovoltaics.
Hybrid Perovskites: Prospects for Concentrator Solar Cells
Publisher: Wiley
Date: 02-2018
Carrier capture and relaxation in Stranski-KrastanowIn
Publisher:
American Physical Society (APS)
Date:
15-07-2000
Publisher: American Physical Society (APS)
Date: 15-07-2000
Magnetic field enhanced terahertz emission from semiconductor surfaces
Publisher: Springer Berlin Heidelberg
Date: 2001
FTU Diagnostic System Based on THz Time-domain Spectroscopy
Publisher: Elsevier BV
Date: 2015
Increased Photoconductivity Lifetime in GaAs Nanowires by Controlled n-Type and p-Type Doping
Publisher: American Chemical Society (ACS)
Date: 14-03-2016
Abstract: Controlled doping of GaAs nanowires is crucial for the development of nanowire-based electronic and optoelectronic devices. Here, we present a noncontact method based on time-resolved terahertz photoconductivity for assessing n- and p-type doping efficiency in nanowires. Using this technique, we measure extrinsic electron and hole concentrations in excess of 10(18) cm(-3) for GaAs nanowires with n-type and p-type doped shells. Furthermore, we show that controlled doping can significantly increase the photoconductivity lifetime of GaAs nanowires by over an order of magnitude: from 0.13 ns in undoped nanowires to 3.8 and 2.5 ns in n-doped and p-doped nanowires, respectively. Thus, controlled doping can be used to reduce the effects of parasitic surface recombination in optoelectronic nanowire devices, which is promising for nanowire devices, such as solar cells and nanowire lasers.
Si and C delta-doping for device applications
Publisher: Elsevier BV
Date: 12-1998
CsPbBr3 Nanocrystal Films: Deviations from Bulk Vibrational and Optoelectronic Properties
Publisher: Wiley
Date: 05-03-2020
Large-Area, Highly Uniform Evaporated Formamidinium Lead Triiodide Thin Films for Solar Cells
Publisher: American Chemical Society (ACS)
Date: 14-11-2017
Enhancement of THz emission from semiconductor devices
Publisher: IEEE
Date: 2002
Noncontact Measurement of Charge Carrier Lifetime and Mobility in GaN Nanowires
Publisher: American Chemical Society (ACS)
Date: 31-08-2012
DOI: 10.1021/NL301898M
Abstract: The first noncontact photoconductivity measurements of gallium nitride nanowires (NWs) are presented, revealing a high crystallographic and optoelectronic quality achieved by use of catalyst-free molecular beam epitaxy. In comparison with bulk material, the NWs exhibit a long conductivity lifetime (>2 ns) and a high mobility (820 ± 120 cm(2)/(V s)). This is due to the weak influence of surface traps with respect to other III-V semiconducting NWs and to the favorable crystalline structure of the NWs achieved via strain-relieved growth.
Modulation Doping of GaAs/AlGaAs Core–Shell Nanowires With Effective Defect Passivation and High Electron Mobility
Publisher: American Chemical Society (ACS)
Date: 28-01-2015
DOI: 10.1021/NL504566T
Abstract: Reliable doping is required to realize many devices based on semiconductor nanowires. Group III-V nanowires show great promise as elements of high-speed optoelectronic devices, but for such applications it is important that the electron mobility is not compromised by the inclusion of dopants. Here we show that GaAs nanowires can be n-type doped with negligible loss of electron mobility. Molecular beam epitaxy was used to fabricate modulation-doped GaAs nanowires with Al0.33Ga0.67As shells that contained a layer of Si dopants. We identify the presence of the doped layer from a high-angle annular dark field scanning electron microscopy cross-section image. The doping density, carrier mobility, and charge carrier lifetimes of these n-type nanowires and nominally undoped reference s les were determined using the noncontact method of optical pump terahertz probe spectroscopy. An n-type extrinsic carrier concentration of 1.10 ± 0.06 × 10(16) cm(-3) was extracted, demonstrating the effectiveness of modulation doping in GaAs nanowires. The room-temperature electron mobility was also found to be high at 2200 ± 300 cm(2) V(-1) s(-1) and importantly minimal degradation was observed compared with undoped reference nanowires at similar electron densities. In addition, modulation doping significantly enhanced the room-temperature photoconductivity and photoluminescence lifetimes to 3.9 ± 0.3 and 2.4 ± 0.1 ns respectively, revealing that modulation doping can passivate interfacial trap states.
The application of one-dimensional nanostructures in terahertz frequency devices
Publisher: AIP Publishing
Date: 03-11-2021
DOI: 10.1063/5.0060797
Abstract: One-dimensional nanostructures commonly refer to nanomaterials with a large length-to-diameter ratio, such as nanowires, nanotubes, nanorods, and nanopillars. The nanoscale lateral dimensions and high aspect ratios of these (quasi) one-dimensional nanostructures result in fascinating optical and electrical properties, including strongly anisotropic optical absorption, controlled directionality of light emission, confined charge-carrier transport and/or ballistic transport, which make one-dimensional nanostructures ideal building blocks for applications in highly integrated photonic, electronic, and optoelectronic systems. In this article, we review recent developments of very high (terahertz) frequency devices based on these one-dimensional nanostructures, particularly focusing on carbon nanotubes and semiconductor nanowires. We discuss state-of-the-art nanomaterials synthesis, device-fabrication techniques, device-operating mechanisms, and device performance. The combination of nanotechnology and terahertz science is a nascent research field which has created advanced THz sources, detectors, and modulators, leading to terahertz systems with extended functionalities. The goal of this article is to present the up-to-date worldwide status of this field and to highlight the current challenges and future opportunities.
Effects of magnetic field and optical fluence on terahertz emission in gallium arsenide
Publisher: American Physical Society (APS)
Date: 26-10-2001
Superfocusing of terahertz waves
Publisher: Springer Science and Business Media LLC
Date: 2007
Modulation of terahertz polarization on picosecond timescales using polymer-encapsulated semiconductor nanowires
Publisher: OSA
Date: 2017
The effect of ion mass on irradiation induced intermixing of GaAs/AlGaAs quantum wells
Publisher: SPIE
Date: 17-09-1998
DOI: 10.1117/12.321942
Alumina Nanoparticle Interfacial Buffer Layer for Low‐Bandgap Lead‐Tin Perovskite Solar Cells
Publisher: Wiley
Date: 22-05-2023
Abstract: Mixed lead‐tin (Pb:Sn) halide perovskites are promising absorbers with narrow‐bandgaps (1.25–1.4 eV) suitable for high‐efficiency all‐perovskite tandem solar cells. However, solution processing of optimally thick Pb:Sn perovskite films is notoriously difficult in comparison with their neat‐Pb counterparts. This is partly due to the rapid crystallization of Sn‐based perovskites, resulting in films that have a high degree of roughness. Rougher films are harder to coat conformally with subsequent layers using solution‐based processing techniques leading to contact between the absorber and the top metal electrode in completed devices, resulting in a loss of V OC , fill factor, efficiency, and stability. Herein, this study employs a non‐continuous layer of alumina nanoparticles distributed on the surface of rough Pb:Sn perovskite films. Using this approach, the conformality of the subsequent electron‐transport layer, which is only tens of nanometres in thickness is improved. The overall maximum‐power‐point‐tracked efficiency improves by 65% and the steady‐state V OC improves by 28%. Application of the alumina nanoparticles as an interfacial buffer layer also results in highly reproducible Pb:Sn solar cell devices while simultaneously improving device stability at 65 °C under full spectrum simulated solar irradiance. Aged devices show a six‐fold improvement in stability over pristine Pb:Sn devices, increasing their lifetime to 120 h.
Formation Dynamics of CH3NH3PbI3 Perovskite Following Two-Step Layer Deposition
Publisher: American Chemical Society (ACS)
Date: 17-12-2015
DOI: 10.1021/ACS.JPCLETT.5B02495
Abstract: Hybrid metal-halide perovskites have emerged as a leading class of semiconductors for optoelectronic devices because of their desirable material properties and versatile fabrication methods. However, little is known about the chemical transformations that occur in the initial stages of perovskite crystal formation. Here we follow the real-time formation dynamics of MAPbI3 from a bilayer of lead iodide (PbI2) and methylammonium iodide (MAI) deposited through a two-step thermal evaporation process. By lowering the substrate temperature during deposition, we are able to initially inhibit intermixing of the two layers. We subsequently use infrared and visible light transmission, X-ray diffraction, and photoluminescence lifetime measurements to reveal the room-temperature transformations that occur in vacuum and ambient air, as MAI diffuses into the PbI2 lattice to form MAPbI3. In vacuum, the transformation to MAPbI3 is incomplete as unreacted MAI is retained in the film. However, exposure to moist air allows for conversion of the unreacted MAI to MAPbI3, demonstrating that moisture is essential in making MAI more mobile and thus aiding perovskite crystallization. These dynamic processes are reflected in the observed charge-carrier lifetimes, which strongly fluctuate during periods of large ion migration but steadily increase with improving crystallinity.
Revealing the origin of voltage loss in mixed-halide perovskite solar cells
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/C9EE02162K
Abstract: The loss from halide-segregation in wide bandgap perovskite solar cells is quantified, revealing that the performance bottleneck currently is, in fact, non-radiative recombination.
THz modulators and detectors based on semiconductor nanowires
Publisher: IEEE
Date: 08-2017
Charge-carrier dynamics in vapour-deposited films of the organolead halide perovskite CH3NH3PbI3−xClx
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4EE01358A
Abstract: High charge-carrier mobilities and recombination lifetimes are revealed for CH 3 NH 3 PbI 3−x Cl x films made by dual-source evaporation. Extracted diffusion lengths approach 3 microns, underlining the high suitability of the evaporated perovskite for planar-heterojunction solar cells.
Charge-carrier dynamics in hybrid metal halide perovskites for photovoltaics and light emission
Publisher: IEEE
Date: 08-2017
Light Induced Recovery of Polymer Field Effect Transistors
Publisher: IEEE
Date: 09-2006
Conformational changes of photoactive yellow protein monitored by terahertz spectroscopy
Publisher: Elsevier BV
Date: 04-2008
Effects of anodic oxide induced intermixing on the structural and optical properties of quantum wire structure grown on nonplanar GaAs substrate
Publisher: AIP Publishing
Date: 11-1996
DOI: 10.1063/1.363546
Abstract: Effects of anodic oxide induced intermixing on the structural and optical properties of stacked GaAs quantum wire (QWR) structures grown on a sawtooth-type nonplanar GaAs substrate are investigated. Cross-sectional transmission electron microscope (XTEM) observation, temperature dependent photoluminescence (PL) and cathodoluminescence (CL) imaging were used. Intermixing was achieved by pulsed anodic oxidation of the GaAs cap layer and subsequent rapid thermal annealing, was verified by XTEM analysis. A significant enhancement of QWR PL is observed accompanied by a notable blueshift of the sidewall quantum well (SQWL) PL due to the intermixing. Furthermore, an extended necking region is observed after the intermixing by spatially resolved CL. The temperature dependence of the PL intensities of both SQWL and QWR show maxima at approximately T∼110 K indicating the role of the extended necking region in feeding carriers to SQWL and QWR.
Low-energy vibrational modes in phenylene oligomers studied by THz time-domain spectroscopy
Publisher: Elsevier BV
Date: 08-2003
Terahertz spectroscopy of modulation doped core-shell GaAs/AlGaAs nanowires
Publisher: IEEE
Date: 08-2015
Ultralow Surface Recombination Velocity in InP Nanowires Probed by Terahertz Spectroscopy
Publisher: American Chemical Society (ACS)
Date: 13-09-2012
DOI: 10.1021/NL3026828
Abstract: Using transient terahertz photoconductivity measurements, we have made noncontact, room temperature measurements of the ultrafast charge carrier dynamics in InP nanowires. InP nanowires exhibited a very long photoconductivity lifetime of over 1 ns, and carrier lifetimes were remarkably insensitive to surface states despite the large nanowire surface area-to-volume ratio. An exceptionally low surface recombination velocity (170 cm/s) was recorded at room temperature. These results suggest that InP nanowires are prime candidates for optoelectronic devices, particularly photovoltaic devices, without the need for surface passivation. We found that the carrier mobility is not limited by nanowire diameter but is strongly limited by the presence of planar crystallographic defects such as stacking faults in these predominantly wurtzite nanowires. These findings show the great potential of very narrow InP nanowires for electronic devices but indicate that improvements in the crystallographic uniformity of InP nanowires will be critical for future nanowire device engineering.
Optoelectronics: Fast silicon photodiodes
Publisher: Springer Science and Business Media LLC
Date: 28-04-2017
Solvent-Free Method for Defect Reduction and Improved Performance of p-i-n Vapor-Deposited Perovskite Solar Cells
Publisher: American Chemical Society (ACS)
Date: 09-05-2022
Extracting the Key Electrical Properties of Semiconductors using Optical Pump Terahertz Probe Spectroscopy
Publisher: IEEE
Date: 09-2016
Static Electrification by Nonwetting Liquids. Contact Charging and Contact Angles
Publisher: American Chemical Society (ACS)
Date: 10-1995
DOI: 10.1021/LA00010A083
Single GaAs/AlGaAs nanowire photoconductive terahertz detectors
Publisher: IEEE
Date: 12-2014
Modification of the fluorinated tin oxide/electron-transporting material interface by a strong reductant and its effect on perovskite solar cell efficiency
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8ME00031J
Abstract: An organometallic reductant affords ohmic contact between FTO and a perylene electron-transport material.
Transmission and emission terahertz time-domain spectroscopy with polarisation-sensitive photoconductive receivers
Publisher: IEEE
Date: 09-2007
The development of terahertz sources and their applications
Publisher: IOP Publishing
Date: 16-10-2002
DOI: 10.1088/0031-9155/47/21/302
Abstract: The terahertz region of the electromagnetic spectrum spans the frequency range between the mid-infrared and the millimetre/microwave. This region has not been exploited fully to date owing to the limited number of suitable (in particular, coherent) radiation sources and detectors. Recent demonstrations, using pulsed near-infrared femtosecond laser systems, of the viability of THz medical imaging and spectroscopy have sparked international interest yet much research still needs to be undertaken to optimize both the power and bandwidth in such THz systems. In this paper, we review how femtosecond near-infrared laser pulses can be converted into broad band THz radiation using semiconductor crystals, and discuss in depth the optimization of one specific generation mechanism based on ultra-fast transport of electrons and holes at a semiconductor surface. We also outline a few of the opportunities for a technology that can address a erse range of challenges spanning the physical and biological sciences, and note the continuing need for the development of solid state, continuous wave, THz sources which operate at room temperature.
Broadband Single-Nanowire Photoconductive Terahertz Detectors
Publisher: OSA
Date: 2017
Unveiling Temperature-Dependent Scattering Mechanisms in Semiconductor Nanowires Using Optical-Pump Terahertz-Probe Spectroscopy
Publisher: IEEE
Date: 09-2019
Polarization-sensitive terahertz detection by multicontact photoconductive receivers
Publisher: AIP Publishing
Date: 16-06-2005
DOI: 10.1063/1.1951051
Abstract: We have developed a terahertz radiation detector that measures both the litude and polarization of the electric field as a function of time. The device is a three-contact photoconductive receiver designed so that two orthogonal electric-field components of an arbitrary polarized electromagnetic wave may be detected simultaneously. The detector was fabricated on Fe+ ion-implanted InP. Polarization-sensitive detection is demonstrated with an extinction ratio better than 100:1. This type of device will have immediate application in studies of birefringent and optically active materials in the far-infrared region of the spectrum.
Generation of high-power terahertz pulses in a prism
Publisher: Optica Publishing Group
Date: 11-2002
DOI: 10.1364/OL.27.001935
Abstract: A compact, high-power emitter of half-cycle terahertz (THz) radiation is demonstrated. The device consists of an epitaxial InAs emitter upon a GaAs prism and produces THz pulses that are 20 times more powerful than those from conventional planar InAs emitters. This improvement is a direct result of reorienting the transient THz dipole such that its axis is not perpendicular to the emitting surface.
Charge selective contacts, mobile ions and anomalous hysteresis in organic–inorganic perovskite solar cells
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4MH00238E
Abstract: “Compact layer-free” perovskite devices yield negligible stabilised power output, in comparison to those with charge selective contacts, elucidating mechanism for hysteresis.
Towards higher electron mobility in modulation doped GaAs/AlGaAs core shell nanowires
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7NR00680B
Abstract: Precise control over the electrical conductivity of semiconductor nanowires is a crucial prerequisite for implementation into novel electronic and optoelectronic devices.
Ultrafast Excited-State Localization in Cs2AgBiBr6 Double Perovskite
Publisher: American Chemical Society (ACS)
Date: 30-03-2021
Vibrational Properties of the Organic–Inorganic Halide Perovskite CH3NH3PbI3 from Theory and Experiment: Factor Group Analysis, First-Principles Calculations, and Low-
Publisher: American Chemical Society (ACS)
Date: 06-11-2015
Charge‐Carrier Dynamics, Mobilities, and Diffusion Lengths of 2D–3D Hybrid Butylammonium–Cesium–Formamidinium Lead Halide Perovskites
Publisher: Wiley
Date: 20-06-2019
Formamidinium lead trihalide: a broadly tunable perovskite for efficient planar heterojunction solar cells
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C3EE43822H
Conductivity of nanoporous InP membranes investigated using terahertz spectroscopy
Publisher: IEEE
Date: 09-2007
Crystallization of CsPbBr3 single crystals in water for X-ray detection
Publisher: Springer Science and Business Media LLC
Date: 09-03-2021
DOI: 10.1038/S41467-021-21805-0
Abstract: Metal halide perovskites have fascinated the research community over the past decade, and demonstrated unprecedented success in optoelectronics. In particular, perovskite single crystals have emerged as promising candidates for ionization radiation detection, due to the excellent opto-electronic properties. However, most of the reported crystals are grown in organic solvents and require high temperature. In this work, we develop a low-temperature crystallization strategy to grow CsPbBr 3 perovskite single crystals in water. Then, we carefully investigate the structure and optoelectronic properties of the crystals obtained, and compare them with CsPbBr 3 crystals grown in dimethyl sulfoxide. Interestingly, the water grown crystals exhibit a distinct crystal habit, superior charge transport properties and better stability in air. We also fabricate X-ray detectors based on the CsPbBr 3 crystals, and systematically characterize their device performance. The crystals grown in water demonstrate great potential for X-ray imaging with enhanced performance metrics.
Unveiling the Influence of pH on the Crystallization of Hybrid Perovskites, Delivering Low Voltage Loss Photovoltaics
Publisher: Elsevier BV
Date: 10-2017
Photovoltaic mixed-cation lead mixed-halide perovskites: links between crystallinity, photo-stability and electronic properties
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C6EE03014A
Abstract: We establish compositional effects on stability, crystallinity, charge-carrier life times and mobilities in mixed-cation lead iodide-bromide perovskites as band gap tunable materials for multi-junction photovoltaic cells.
Selective dielectrophoretic manipulation of surface-immobilized DNA molecules
Publisher: IOP Publishing
Date: 18-06-2003
Electron mobilities approaching bulk limits in surface-free GaAs nanowires
Publisher: American Chemical Society (ACS)
Date: 26-09-2014
DOI: 10.1021/NL503043P
Abstract: Achieving bulk-like charge carrier mobilities in semiconductor nanowires is a major challenge facing the development of nanowire-based electronic devices. Here we demonstrate that engineering the GaAs nanowire surface by overcoating with optimized AlGaAs shells is an effective means of obtaining exceptionally high carrier mobilities and lifetimes. We performed measurements of GaAs/AlGaAs core-shell nanowires using optical pump-terahertz probe spectroscopy: a noncontact and accurate probe of carrier transport on ultrafast time scales. The carrier lifetimes and mobilities both improved significantly with increasing AlGaAs shell thickness. Remarkably, optimized GaAs/AlGaAs core-shell nanowires exhibited electron mobilities up to 3000 cm(2) V(-1) s(-1), reaching over 65% of the electron mobility typical of high quality undoped bulk GaAs at equivalent photoexcited carrier densities. This points to the high interface quality and the very low levels of ionized impurities and lattice defects in these nanowires. The improvements in mobility were concomitant with drastic improvements in photoconductivity lifetime, reaching 1.6 ns. Comparison of photoconductivity and photoluminescence dynamics indicates that midgap GaAs surface states, and consequently surface band-bending and depletion, are effectively eliminated in these high quality heterostructures.
Impact of Tin Fluoride Additive on the Properties of Mixed Tin‐Lead Iodide Perovskite Semiconductors
Publisher: Wiley
Date: 20-09-2020
Theory of magnetic-field enhancement of surface-field terahertz emission
Publisher: AIP Publishing
Date: 15-02-2002
DOI: 10.1063/1.1433187
Abstract: We present a theoretical treatment of surface–field THz generation in semiconductors, which explains the power enhancement observed when a magnetic field is applied. Our model consists of two parts: a Monte Carlo simulation of the dynamics of carriers generated by a subpicosecond optical pulse, and a calculation of the resulting THz radiation emitted through the semiconductor surface. The magnetic field deflects the motion of the carriers, producing a component of the THz dipole parallel to the surface. This causes the power transmitted through the surface to be increased by more than one order of magnitude.
III–V semiconductor nanowires for optoelectronic device applications
Publisher: Elsevier BV
Date: 03-2011
Cs2InAgCl6: A New Lead-Free Halide Double Perovskite with Direct Band Gap
Publisher: American Chemical Society (ACS)
Date: 31-01-2017
DOI: 10.1021/ACS.JPCLETT.6B02682
Abstract: A
Interplay of Structural and Optoelectronic Properties in Formamidinium Mixed Tin–Lead Triiodide Perovskites
Publisher: Wiley
Date: 21-06-2018
Preface to Special Topic: Frontiers on THz photonic devices
Publisher: AIP Publishing
Date: 05-2018
DOI: 10.1063/1.5039879
Abstract: Terahertz (THz) photonic devices are now exploiting emerging materials systems, while novel device designs utilise plasmonic effects, nanophotinics, and metamaterials. The scope of this special topic highlights and reviews the recent cutting-edge THz photonic devices which have been revolutionised from the advances in the above research areas.
Transient terahertz spectroscopy of mono- and tri-layer CVD-grown MoS 2
Publisher: IEEE
Date: 09-2013
Growth modes and quantum confinement in ultrathin vapour-deposited MAPbI3 films
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9NR04104D
Abstract: We examine the initial growth modes of MAPbI 3 films deposited by co-evaporation, with average thicknesses from 2–320 nm. Electronic quantum confinement effects are observed for films with average thickness below 40 nm.
The origin of an efficiency improving “light soaking” effect in SnO2 based solid-state dye-sensitized solar cells
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2EE22320A
Raman Spectrum of the Organic–Inorganic Halide Perovskite CH3NH3PbI3 from First Principles and High-Resolution Low-Temperature Raman Measurements
Publisher: American Chemical Society (ACS)
Date: 05-09-2018
Terahertz Conductivity Analysis for Highly Doped Thin-Film Semiconductors
Publisher: Springer Science and Business Media LLC
Date: 15-09-2020
DOI: 10.1007/S10762-020-00739-6
Abstract: The analysis of terahertz transmission through semiconducting thin films has proven to be an excellent tool for investigating optoelectronic properties of novel materials. Terahertz time-domain spectroscopy (THz-TDS) can provide information about phonon modes of the crystal, as well as the electrical conductivity of the s le. When paired with photoexcitation, optical-pump-THz-probe (OPTP) technique can be used to gain an insight into the transient photoconductivity of the semiconductor, revealing the dynamics and the mobility of photoexcited charge carriers. As the relation between the conductivity of the material and the THz transmission function is generally complicated, simple analytical expressions have been developed to enable straightforward calculations of frequency-dependent conductivity from THz-TDS data in the regime of optically thin s les. Here, we assess the accuracy of these approximated analytical formulas in thin films of highly doped semiconductors, finding significant deviations of the calculated photoconductivity from its actual value in materials with background conductivity comparable to 10 2 Ω − 1 cm − 1 . We propose an alternative analytical expression, which greatly improves the accuracy of the estimated value of the real photoconductivity, while remaining simple to implement experimentally. Our approximation remains valid in thin films with high dark conductivity of up to 10 4 Ω − 1 cm − 1 and provides a very high precision for calculating photoconductivity up to 10 4 Ω − 1 cm − 1 , and therefore is highly relevant for studies of photoexcited charge-carrier dynamics in electrically doped semiconductors. Using the ex le of heavily doped thin films of tin-iodide perovskites, we show a simple experimental method of implementing our correction and find that the commonly used expression for photoconductivity could result in an underestimate of charge-carrier mobility by over 50%.
Improved performance of GaAs-based terahertz emitters
Publisher: IEEE
Date: 09-2010
Three-dimensional cross-nanowire networks recover full terahertz state
Publisher: American Association for the Advancement of Science (AAAS)
Date: 05-2020
Abstract: Terahertz (THz) radiation is an interesting region of the electromagnetic spectrum lying between microwaves and infrared. Non-ionizing and transparent to most fabrics, it is finding application in security screening and imaging but is also being developed for communication and chemical sensing. To date, most THz detectors have focused just on signal intensity, an effort that discards half the signal in terms of the full optical state, including polarization. Peng et al. developed a THz detector based on crossed nanowires (arranged in a hash structure) that is capable of resolving the full state of the THz light. The approach provides a nanophotonic platform for the further development of THz-based technologies. Science , this issue p. 510
Atomic-scale microstructure of metal halide perovskite
Publisher: American Association for the Advancement of Science (AAAS)
Date: 30-10-2020
Abstract: The optoelectronic and photovoltaic applications of polycrystalline hybrid metal halide perovskite films are notable because grain boundaries in most materials cause scattering of charge carriers that decreases performance. Electron microscopy studies of these materials have been hindered by their rapid structural degradation under intense electron beams. Rothmann et al. now present an atomic crystallographic structure of formamidinium lead triiodide (FAPbI 3 ) polycrystalline thin films obtained by low-electron-dose scanning transmission electron microscopy with advanced image processing. The crystal structure sustains substoichiometry in the A-site cation, has a nearly perfect crystallographic alignment between PbI 2 impurity phases and the FAPbI 3 perovskite, and has atomically clean grain boundaries between polycrystalline domains. These features help to explain the films' surprising regenerative ability, their benign grain boundaries where strain and dislocations appear mostly absent, and why excess lead-iodide precursor can be counterintuitively beneficial. Science , this issue p. eabb5940
Quantitative measurement of a 3-component mixture based on THz spectra
Publisher: SPIE
Date: 13-03-2012
DOI: 10.1117/12.919981
Synergistic Surface Modification of Tin–Lead Perovskite Solar Cells
Publisher: Wiley
Date: 22-01-2023
Abstract: Interfaces in thin‐film photovoltaics play a pivotal role in determining device efficiency and longevity. In this work, the top surface treatment of mixed tin–lead (≈1.26 eV) halide perovskite films for p–i–n solar cells is studied. Charge extraction is promoted by treating the perovskite surface with piperazine. This compound reacts with the organic cations at the perovskite surface, modifying the surface structure and tuning the interfacial energy level alignment. In addition, the combined treatment with C 60 pyrrolidine tris‐acid (CPTA) reduces hysteresis and leads to efficiencies up to 22.7%, with open‐circuit voltage values reaching 0.90 V, ≈92% of the radiative limit for the bandgap of this material. The modified cells also show superior stability, with unencapsulated cells retaining 96% of their initial efficiency after h of storage in N 2 and encapsulated cells retaining 90% efficiency after h of storage in air. Intriguingly, CPTA preferentially binds to Sn 2+ sites at film surface over Pb 2+ due to the energetically favored exposure of the former, according to first‐principles calculations. This work provides new insights into the surface chemistry of perovskite films in terms of their structural, electronic, and defect characteristics and this knowledge is used to fabricate state‐of‐the‐art solar cells.
Environment induced variation in the photoconductivity of graphene observed by terahertz spectroscopy
Publisher: IEEE
Date: 09-2012
Extraction of the anisotropic dielectric properties of materials from polarization-resolved terahertz time-domain spectra
Publisher: IOP Publishing
Date: 14-08-2009
Low-energy collective dynamics of charge stripes in the doped nickelate La2-xSrxNiO4+delta observed with optical conductivity measurements
Publisher: American Physical Society (APS)
Date: 14-05-2008
Terahertz photoconductivity of mobile electrons in nanoporous InP honeycombs
Publisher: American Physical Society (APS)
Date: 26-08-2008
A piperidinium salt stabilizes efficient metal-halide perovskite solar cells
Publisher: American Association for the Advancement of Science (AAAS)
Date: 03-07-2020
Abstract: Ionic liquids have been shown to stabilize organic-inorganic perovskite solar cells with metal oxide carrier-transport layers, but they are incompatible with more readily processible organic analogs. Lin et al. found that an ionic solid, a piperidinium salt, enhanced the efficiency of positive-intrinsic-negative layered perovskite solar cells with organic electron and hole extraction layers. Aggressive aging testing showed that this additive retarded segregation into impurity phases and pinhole formation in the perovskite layer. Science , this issue p. 96
Plasmonic‐Induced Photon Recycling in Metal Halide Perovskite Solar Cells
Publisher: Wiley
Date: 08-07-2015
Thermally stimulated luminescence in ion-implanted GaAs
Publisher: Elsevier BV
Date: 03-2002
Hot electron cooling in InSb probed by ultrafast time-resolved terahertz cyclotron resonance
Publisher: American Physical Society (APS)
Date: 28-06-2021
Charge carrier recombination channels in the low-temperature phase of organic-inorganic lead halide perovskite thin films
Publisher: AIP Publishing
Date: 08-2014
DOI: 10.1063/1.4891595
Abstract: The optoelectronic properties of the mixed hybrid lead halide perovskite CH3NH3PbI3−xClx have been subject to numerous recent studies related to its extraordinary capabilities as an absorber material in thin film solar cells. While the greatest part of the current research concentrates on the behavior of the perovskite at room temperature, the observed influence of phonon-coupling and excitonic effects on charge carrier dynamics suggests that low-temperature phenomena can give valuable additional insights into the underlying physics. Here, we present a temperature-dependent study of optical absorption and photoluminescence (PL) emission of vapor-deposited CH3NH3PbI3−xClx exploring the nature of recombination channels in the room- and the low-temperature phase of the material. On cooling, we identify an up-shift of the absorption onset by about 0.1 eV at about 100 K, which is likely to correspond to the known tetragonal-to-orthorhombic transition of the pure halide CH3NH3PbI3. With further decreasing temperature, a second PL emission peak emerges in addition to the peak from the room-temperature phase. The transition on heating is found to occur at about 140 K, i.e., revealing significant hysteresis in the system. While PL decay lifetimes are found to be independent of temperature above the transition, significantly accelerated recombination is observed in the low-temperature phase. Our data suggest that small inclusions of domains adopting the room-temperature phase are responsible for this behavior rather than a spontaneous increase in the intrinsic rate constants. These observations show that even sparse lower-energy sites can have a strong impact on material performance, acting as charge recombination centres that may detrimentally affect photovoltaic performance but that may also prove useful for optoelectronic applications such as lasing by enhancing population inversion.
Bandgap‐Tunable Cesium Lead Halide Perovskites with High Thermal Stability for Efficient Solar Cells
Publisher: Wiley
Date: 02-02-2016
Wavelength shifting of adjacent quantum wells in V-groove quantum wire structure by selective implantation and annealing
Publisher: AIP Publishing
Date: 02-2000
DOI: 10.1063/1.372051
Abstract: Intermixing induced by selective implantation was used to modify the two-dimensional (2D) quantum wells in the V-grooved quantum wire structure. Photoluminescence measurement of the implanted s les shows the obvious blueshift of the interband transition energy while quantum wire is not influenced by implantation. So the selective implantation method has been demonstrated in this article as a useful technique to isolate the energy levels of quantum wire structure from its neighbor 2D structures, which is preferred for the optoelectronic device application of quantum wire.
Halide Segregation in Mixed-Halide Perovskites: Influence of A-Site Cations
Publisher: American Chemical Society (ACS)
Date: 02-2021
Interdiffused quantum-well infrared photodetectors for color sensitive arrays
Publisher: AIP Publishing
Date: 16-08-1999
DOI: 10.1063/1.124555
Abstract: Proton implantation and rapid thermal annealing were used to tune the infrared spectral response of quantum-well infrared photodetectors (QWIP) by up to 1.4 μm. Multiple proton implants at energies between 200 and 420 keV were used to create homogeneous quantum-well intermixing throughout the device’s multiple-quantum-well structure. Photoluminescence and spectral response measurements were used to study the effect of proton implantation on QWIPs for a series of doses up to 3.5×1015 protons cm−2. By using a mask during implantation, a method of constructing a color sensitive array is proposed.
Light Absorption and Recycling in Hybrid Metal Halide Perovskite Photovoltaic Devices
Publisher: Wiley
Date: 03-02-2020
Simulation of terahertz generation at semiconductor surfaces
Publisher: American Physical Society (APS)
Date: 18-03-2002
Magnetic-field-induced enhancement of terahertz emission from III–V semiconductor surfaces
Publisher: Elsevier BV
Date: 04-2022
Thermally Stable Passivation toward High Efficiency Inverted Perovskite Solar Cells
Publisher: American Chemical Society (ACS)
Date: 10-2020
Ultrafast Dynamics of Exciton Formation in Semiconductor Nanowires
Publisher: Wiley
Date: 22-03-2012
Abstract: The dynamics of free electron-hole pairs and excitons in GaAs-AlGaAs-GaAs core-shell-skin nanowires is investigated using femtosecond transient photoluminescence spectroscopy at 10 K. Following nonresonant excitation, a bimolecular interconversion of the initially generated electron-hole plasma into an exciton population is observed. This conducting-to-insulating transition appears to occur gradually over electron-hole charge pair densities of 2-4 × 10(16) cm(-3) . The smoothness of the Mott transition is attributed to the slow carrier-cooling during the bimolecular interconversion of free charge carriers into excitons and to the presence of chemical-potential fluctuations leading to inhomogeneous spectral characteristics. These results demonstrate that high-quality nanowires are model systems for investigating fundamental scientific effects in 1D heterostructures.
Metal composition influences optoelectronic quality in mixed-metal lead–tin triiodide perovskite solar absorbers
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0EE00132E
Abstract: By correlating photovoltaic and material properties with metal content, we identify compositional ranges of low and high optoelectronic quality in (FA 0.83 Cs 0.17 )(Pb 1−y Sn y )I 3 perovskites.
Carrier dynamics in ion-implanted semiconductors studied by simulation and observation of terahertz emission - art. no. 61180K
Publisher: SPIE
Date: 09-02-2006
DOI: 10.1117/12.644074
Terahertz emission from lateral photo-Dember currents
Publisher: Optica Publishing Group
Date: 24-02-2010
DOI: 10.1364/OE.18.004939
Highly Crystalline Methylammonium Lead Tribromide Perovskite Films for Efficient Photovoltaic Devices
Publisher: American Chemical Society (ACS)
Date: 30-04-2018
Enhancement of ultrafast conductivity in surface-passivated GaAs
Publisher: OSA
Date: 2007
Control over Crystal Size in Vapor Deposited Metal-Halide Perovskite Films
Publisher: American Chemical Society (ACS)
Date: 04-02-2020
Terahertz probe of carrier trapping in polymer transistors
Publisher: OSA
Date: 2007
Polarisation-sensitive terahertz detectors
Publisher: IEEE
Date: 2005
Direct Observation of Charge-Carrier Heating at WZ–ZB InP Nanowire Heterojunctions
Publisher: American Chemical Society (ACS)
Date: 12-08-2013
DOI: 10.1021/NL402050Q
Abstract: We have investigated the dynamics of hot charge carriers in InP nanowire ensembles containing a range of densities of zinc-blende inclusions along the otherwise wurtzite nanowires. From time-dependent photoluminescence spectra, we extract the temperature of the charge carriers as a function of time after nonresonant excitation. We find that charge-carrier temperature initially decreases rapidly with time in accordance with efficient heat transfer to lattice vibrations. However, cooling rates are subsequently slowed and are significantly lower for nanowires containing a higher density of stacking faults. We conclude that the transfer of charges across the type II interface is followed by release of additional energy to the lattice, which raises the phonon bath temperature above equilibrium and impedes the carrier cooling occurring through interaction with such phonons. These results demonstrate that type II heterointerfaces in semiconductor nanowires can sustain a hot charge-carrier distribution over an extended time period. In photovoltaic applications, such heterointerfaces may hence both reduce recombination rates and limit energy losses by allowing hot-carrier harvesting.
Efficient perovskite solar cells by metal ion doping
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6EE01969B
Abstract: Realizing the theoretical limiting power conversion efficiency (PCE) in perovskite solar cells requires a better understanding and control over the fundamental loss processes occurring in the bulk of the perovskite layer and at the internal semiconductor interfaces in devices.
Optical Description of Mesostructured Organic–Inorganic Halide Perovskite Solar Cells
Publisher: American Chemical Society (ACS)
Date: 12-12-2014
DOI: 10.1021/JZ502351S
Abstract: Herein we describe both theoretically and experimentally the optical response of solution-processed organic-inorganic halide perovskite solar cells based on mesostructured scaffolds. We develop a rigorous theoretical model using a method based on the propagation of waves in layered media, which allows visualizing the way in which light is spatially distributed across the device and serves to quantify the fraction of light absorbed by each medium comprising the cell. The discrimination between productive and parasitic absorption yields an accurate determination of the internal quantum efficiency. State-of-the-art devices integrating mesoporous scaffolds infiltrated with perovskite are manufactured and characterized to support the calculations. This combined experimental and theoretical analysis provides a rational understanding of the optical behavior of perovskite cells and can be beneficial for the judicious design of devices with improved performance. Notably, our model justifies the presence of a solid perovskite capping layer in all of the highest efficiency perovskite solar cells based on thinner mesoporous scaffolds.
Understanding the Degradation of Methylenediammonium and Its Role in Phase-Stabilizing Formamidinium Lead Triiodide
Publisher: American Chemical Society (ACS)
Date: 28-04-2023
DOI: 10.1021/JACS.3C01531
Polymer Transistor Performance Monitored by Terahertz Spectroscopy
Publisher: IEEE
Date: 09-2006
Charge-Carrier Dynamics of Solution-Processed Antimony- and Bismuth-Based Chalcogenide Thin Films
Publisher: American Chemical Society (ACS)
Date: 17-02-2023
Ultrafast Charge Separation at a Single-walled Carbon Nanotube – Polymer Interface
Publisher: Springer Science and Business Media LLC
Date: 2011
DOI: 10.1557/OPL.2011.230
Abstract: We report the observation of an ultrafast (~ 430 fs) charge transfer process at the interface between a single-walled carbon nanotube (SWNT) wrapped by a semi-conducting polymer, poly(3-hexylthiophene) (P3HT), creating free polarons on both materials. The addition of excess P3HT as a surrounding network allows these free polarons to be long-lived at room temperature. Our results suggest that SWNT-P3HT blends incorporating only 1% fractions of SWNTs can achieve a charge separation efficiency comparable to a conventional 60:40 P3HT-fullerene blend, provided small-diameter tubes are embedded in an excess P3HT matrix.
Homogeneous Emission Line Broadening in the Organo Lead Halide Perovskite CH3NH3PbI3–xClx
Publisher: American Chemical Society (ACS)
Date: 27-03-2014
DOI: 10.1021/JZ500434P
Abstract: The organic-inorganic hybrid perovskites methylammonium lead iodide (CH3NH3PbI3) and the partially chlorine-substituted mixed halide CH3NH3PbI3-xClx emit strong and broad photoluminescence (PL) around their band gap energy of ∼1.6 eV. However, the nature of the radiative decay channels behind the observed emission and, in particular, the spectral broadening mechanisms are still unclear. Here we investigate these processes for high-quality vapor-deposited films of CH3NH3PbI3-xClx using time- and excitation-energy dependent photoluminescence spectroscopy. We show that the PL spectrum is homogenously broadened with a line width of 103 meV most likely as a consequence of phonon coupling effects. Further analysis reveals that defects or trap states play a minor role in radiative decay channels. In terms of possible lasing applications, the emission spectrum of the perovskite is sufficiently broad to have potential for lification of light pulses below 100 fs pulse duration.
Simulation and optimization of arsenic-implanted THz emitters
Publisher: IEEE
Date: 2004
Electronic Traps and Phase Segregation in Lead Mixed-Halide Perovskite
Publisher: American Chemical Society (ACS)
Date: 27-11-2018
High Charge Carrier Mobilities and Lifetimes in Organolead Trihalide Perovskites
Publisher: Wiley
Date: 20-12-2013
Probing the photophysics of semiconductor nanomaterials using optical pump-terahertz probe spectroscopy: from nanowires to perovskites
Publisher: SPIE
Date: 07-09-2018
DOI: 10.1117/12.2320720
Optimizing the Energy Offset between Dye and Hole-Transporting Material in Solid-State Dye-Sensitized Solar Cells
Publisher: American Chemical Society (ACS)
Date: 20-09-2013
DOI: 10.1021/JP405734F
Terahertz emission and lifetime measurements of ion-implanted semiconductors: Experiment and simulation
Publisher: IEEE
Date: 2006
Improved Performance of GaAs-Based Terahertz Emitters via Surface Passivation and Silicon Nitride Encapsulation
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2011
Role of Ultrafast Torsional Relaxation in the Emission from Polythiophene Aggregates
Publisher: American Chemical Society (ACS)
Date: 07-12-2010
DOI: 10.1021/JZ101026G
Distinguishing cap and core contributions to the photoconductive terahertz response of single gaas based core–shell–cap nanowire detectors,Apvalkalo ir šerdies indėlių atskyrimas teraherciniame gaas šerdies-kevalo-apvalkalo tipo vieno nanolaido detektoriaus fotolaidumo atsake
Publisher: Lithuanian Academy of Sciences
Date: 28-03-2018
DOI: 10.3952/PHYSICS.V58I1.3648
Abstract: GaAs nanowires are promising candidates for advanced optoelectronic devices, despite their high surface recombination velocity and large surface-area-to-volume ratio, which renders them problematic for applications that require efficient charge collection and long charge-carrier lifetimes. Overcoating a bare GaAs nanowire core with an optimized larger-bandgap AlGaAs shell, followed by a capping layer of GaAs to prevent oxidation, has proven an effective way to passivate the nanowire surface and thereby improve electrical properties for enhanced device performance. However, it is difficult to quantify and distinguish the contributions between the nanowire core and cap layer when measuring the optoelectronic properties of a nanowire device. Here, we investigated the photoconductive terahertz (THz) response characteristics of single GaAs/AlGaAs/GaAs core–shell–cap nanowire detectors designed for THz time-domain spectroscopy. We present a detailed study of the contributions of the GaAs cap layer and GaAs core on the ultrafast optoelectronic performance of the detector. We show that both the GaAs cap and core contribute to the photoconductive signal in proportion to their relative volume in the nanowire. By increasing the cap volume ratio to above 90% of the total GaAs volume, a quasi-direct-s ling type photoconductive nanowire detector can be achieved that is highly desirable for low-noise and fast data acquisition detection.
Elucidating the Role of a Tetrafluoroborate‐Based Ionic Liquid at the n‐Type Oxide/Perovskite Interface
Publisher: Wiley
Date: 11-12-2019
Abstract: Halide perovskites are currently one of the most heavily researched emerging photovoltaic materials. Despite achieving remarkable power conversion efficiencies, perovskite solar cells have not yet achieved their full potential, with the interfaces between the perovskite and the charge‐selective layers being where most recombination losses occur. In this study, a fluorinated ionic liquid (IL) is employed to modify the perovskite/SnO 2 interface. Using Kelvin probe and photoelectron spectroscopy measurements, it is shown that depositing the perovskite onto an IL‐treated substrate results in the crystallization of a perovskite film which has a more n‐type character, evidenced by a decrease of the work function and a shift of the Fermi level toward the conduction band. Photoluminescence spectroscopy and time‐resolved microwave conductivity are used to investigate the optoelectronic properties of the perovskite grown on neat and IL‐modified surfaces and it is found that the modified substrate yields a perovskite film which exhibits an order of magnitude lower trap density than the control. When incorporated into solar cells, this interface modification results in a reduction in the current–voltage hysteresis and an improvement in device performance, with the best performing devices achieving steady‐state PCEs exceeding 20%.
Dual-Source Coevaporation of Low-Bandgap FA1–xCsxSn1–yPbyI3 Perovskites for Photovoltaics
Publisher: American Chemical Society (ACS)
Date: 10-10-2019
High irradiance performance of metal halide perovskites for concentrator photovoltaics
Publisher: Springer Science and Business Media LLC
Date: 06-08-2018
Transient Terahertz Conductivity of GaAs Nanowires
Publisher: American Chemical Society (ACS)
Date: 27-06-2007
DOI: 10.1021/NL071162X
A mixed-cation lead mixed-halide perovskite absorber for tandem solar cells
Publisher: American Association for the Advancement of Science (AAAS)
Date: 08-01-2016
Abstract: Improving the performance of conventional single-crystalline silicon solar cells will help increase their adoption. The absorption of bluer light by an inexpensive overlying solar cell in a tandem arrangement would provide a step in the right direction by improving overall efficiency. Inorganic-organic perovskite cells can be tuned to have an appropriate band gap, but these compositions are prone to decomposition. McMeekin et al. show that using cesium ions along with formamidinium cations in lead bromide–iodide cells improved thermal and photostability. These improvements lead to high efficiency in single and tandem cells. Science , this issue p. 151
Solution-Processed All-Perovskite Multi-junction Solar Cells
Publisher: Elsevier BV
Date: 02-2019
Strong Carrier Lifetime Enhancement in GaAs Nanowires Coated with Semiconducting Polymer
Publisher: American Chemical Society (ACS)
Date: 29-11-2012
DOI: 10.1021/NL3034027
Abstract: The ultrafast charge carrier dynamics in GaAs/conjugated polymer type II heterojunctions are investigated using time-resolved photoluminescence spectroscopy at 10 K. By probing the photoluminescence at the band edge of GaAs, we observe strong carrier lifetime enhancement for nanowires blended with semiconducting polymers. The enhancement is found to depend crucially on the ionization potential of the polymers with respect to the Fermi energy level at the surface of the GaAs nanowires. We attribute these effects to electron doping by the polymer which reduces the unsaturated surface-state density in GaAs. We find that when the surface of nanowires is terminated by native oxide, the electron injection across the interface is greatly reduced and such surface doping is absent. Our results suggest that surface engineering via π-conjugated polymers can substantially improve the carrier lifetime in nanowire hybrid heterojunctions with applications in photovoltaics and nanoscale photodetectors.
Phase segregation in mixed-halide perovskites affects charge-carrier dynamics while preserving mobility
Publisher: Springer Science and Business Media LLC
Date: 29-11-2021
DOI: 10.1038/S41467-021-26930-4
Abstract: Mixed halide perovskites can provide optimal bandgaps for tandem solar cells which are key to improved cost-efficiencies, but can still suffer from detrimental illumination-induced phase segregation. Here we employ optical-pump terahertz-probe spectroscopy to investigate the impact of halide segregation on the charge-carrier dynamics and transport properties of mixed halide perovskite films. We reveal that, surprisingly, halide segregation results in negligible impact to the THz charge-carrier mobilities, and that charge carriers within the I-rich phase are not strongly localised. We further demonstrate enhanced lattice anharmonicity in the segregated I-rich domains, which is likely to support ionic migration. These phonon anharmonicity effects also serve as evidence of a remarkably fast, picosecond charge funnelling into the narrow-bandgap I-rich domains. Our analysis demonstrates how minimal structural transformations during phase segregation have a dramatic effect on the charge-carrier dynamics as a result of charge funnelling. We suggest that because such enhanced recombination is radiative, performance losses may be mitigated by deployment of careful light management strategies in solar cells.
Temperature-Dependent Refractive Index of Quartz at Terahertz Frequencies
Publisher: Springer Science and Business Media LLC
Date: 13-09-2018
Choice of polymer matrix for a fast switchable III-V nanowire terahertz modulator
Publisher: Springer Science and Business Media LLC
Date: 03-04-2017
DOI: 10.1557/ADV.2017.280
Impact of the Organic Cation on the Optoelectronic Properties of Formamidinium Lead Triiodide
Publisher: American Chemical Society (ACS)
Date: 23-07-2018
DOI: 10.1021/ACS.JPCLETT.8B01628
Abstract: Metal halide perovskites have proven to be excellent light-harvesting materials in photovoltaic devices whose efficiencies are rapidly improving. Here, we examine the temperature-dependent photon absorption, exciton binding energy, and band gap of FAPbI
Limits to Electrical Mobility in Lead-Halide Perovskite Semiconductors
Publisher: American Chemical Society (ACS)
Date: 06-04-2021
Dependence of Dye Regeneration and Charge Collection on the Pore‐Filling Fraction in Solid‐State Dye‐Sensitized Solar Cells
Publisher: Wiley
Date: 03-09-2013
Abstract: Solid‐state dye‐sensitized solar cells rely on effective infiltration of a solid‐state hole‐transporting material into the pores of a nanoporous TiO 2 network to allow for dye regeneration and hole extraction. Using microsecond transient absorption spectroscopy and femtosecond photoluminescence upconversion spectroscopy, the hole‐transfer yield from the dye to the hole‐transporting material 2,2′,7,7′‐tetrakis( N,N ‐di‐p‐methoxyphenylamine)‐9,9'‐spirobifluorene (spiro‐OMeTAD) is shown to rise rapidly with higher pore‐filling fractions as the dye‐coated pore surface is increasingly covered with hole‐transporting material. Once a pore‐filling fraction of ≈30% is reached, further increases do not significantly change the hole‐transfer yield. Using simple models of infiltration of spiro‐OMeTAD into the TiO 2 porous network, it is shown that this pore‐filling fraction is less than the amount required to cover the dye surface with at least a single layer of hole‐transporting material, suggesting that charge diffusion through the dye monolayer network precedes transfer to the hole‐transporting material. Comparison of these results with device parameters shows that improvements of the power‐conversion efficiency beyond ≈30% pore filling are not caused by a higher hole‐transfer yield, but by a higher charge‐collection efficiency, which is found to occur in steps. The observed sharp onsets in photocurrent and power‐conversion efficiencies with increasing pore‐filling fraction correlate well with percolation theory, predicting the points of cohesive pathway formation in successive spiro‐OMeTAD layers adhered to the pore walls. From percolation theory it is predicted that, for standard mesoporous TiO 2 with 20 nm pore size, the photocurrent should show no further improvement beyond an ≈83% pore‐filling fraction.
Single nanowire terahertz detectors
Publisher: OSA
Date: 2015
Proton implantation and rapid thermal annealing effects on GaAs/AlGaAs quantum well infrared photodetectors
Publisher: Elsevier BV
Date: 11-1999
THz time-domain spectroscopy for tokamak plasma diagnostics
Publisher: AIP Publishing LLC
Date: 2014
DOI: 10.1063/1.4894037
Thermally Stable Perovskite Solar Cells by All-Vacuum Deposition
Publisher: American Chemical Society (ACS)
Date: 23-12-2022
Photoluminescence study of the dynamical properties of GaAs sawtooth superlattices
Publisher: AIP Publishing
Date: 12-1997
DOI: 10.1063/1.366439
Abstract: The dynamic properties of a sawtooth superlattice (δ-doped nipi) were examined by photoluminescence (PL) spectroscopic techniques. The structure was grown on a semi-insulating GaAs substrate by metalorganic vapor phase epitaxy, using C and Si δ-doping. The excitation intensity dependence of the s le’s PL was measured over six decades which produced a shift of 200 meV in the peak of the PL photon energy. The dynamic properties of the sawtooth superlattice were probed using time resolved PL and carrier lifetime measurements. Time resolved PL was measured over 6 orders of magnitude in delay time. The luminescence wavelength from the sawtooth superlattice s le was found to shift to low energies over time after pulsed excitation, indicating the temporal evolution of the band edges. A new and sensitive technique for measuring radiative recombination lifetimes at low excitation intensities was developed. Therefore δ-doped sawtooth superlattices are shown to have a tunable band gap as well as an intensity tunable carrier lifetime.
Trap States, Electric Fields, and Phase Segregation in Mixed‐Halide Perovskite Photovoltaic Devices
Publisher: Wiley
Date: 30-01-2020
Emission of collimated THz pulses from photo-excited semiconductors
Publisher: IOP Publishing
Date: 15-03-2004
Fast electron trapping in anodized TiO<inf>2</inf> nanotubes
Publisher: IEEE
Date: 09-2013
Engineering semiconductor nanowires for photodetection: from visible to terahertz
Publisher: SPIE
Date: 18-09-2018
DOI: 10.1117/12.2320715
Longitudinal electron bunch profile diagnostics at 45 MeV using coherent Smith-Purcell radiation
Publisher: American Physical Society (APS)
Date: 11-09-2006
The 2023 terahertz science and technology roadmap
Publisher: IOP Publishing
Date: 05-04-2023
Abstract: Terahertz (THz) radiation encompasses a wide spectral range within the electromagnetic spectrum that extends from microwaves to the far infrared (100 GHz–∼30 THz). Within its frequency boundaries exist a broad variety of scientific disciplines that have presented, and continue to present, technical challenges to researchers. During the past 50 years, for instance, the demands of the scientific community have substantially evolved and with a need for advanced instrumentation to support radio astronomy, Earth observation, weather forecasting, security imaging, telecommunications, non-destructive device testing and much more. Furthermore, applications have required an emergence of technology from the laboratory environment to production-scale supply and in-the-field deployments ranging from harsh ground-based locations to deep space. In addressing these requirements, the research and development community has advanced related technology and bridged the transition between electronics and photonics that high frequency operation demands. The multidisciplinary nature of THz work was our stimulus for creating the 2017 THz Science and Technology Roadmap (Dhillon et al 2017 J. Phys. D: Appl. Phys. 50 043001). As one might envisage, though, there remains much to explore both scientifically and technically and the field has continued to develop and expand rapidly. It is timely, therefore, to revise our previous roadmap and in this 2023 version we both provide an update on key developments in established technical areas that have important scientific and public benefit, and highlight new and emerging areas that show particular promise. The developments that we describe thus span from fundamental scientific research, such as THz astronomy and the emergent area of THz quantum optics, to highly applied and commercially and societally impactful subjects that include 6G THz communications, medical imaging, and climate monitoring and prediction. Our Roadmap vision draws upon the expertise and perspective of multiple international specialists that together provide an overview of past developments and the likely challenges facing the field of THz science and technology in future decades. The document is written in a form that is accessible to policy makers who wish to gain an overview of the current state of the THz art, and for the non-specialist and curious who wish to understand available technology and challenges. A such, our experts deliver a ‘snapshot’ introduction to the current status of the field and provide suggestions for exciting future technical development directions. Ultimately, we intend the Roadmap to portray the advantages and benefits of the THz domain and to stimulate further exploration of the field in support of scientific research and commercial realisation.
Understanding and suppressing non-radiative losses in methylammonium-free wide-bandgap perovskite solar cells
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D1EE02650J
Abstract: We identify the limiting factors of wide bandgap metal halide perovskite solar cells. To overcome these losses, we developed an efficient optimisation strategy and outline the necessary steps for the continued development of these perovskites.
Intermediate-phase engineering via dimethylammonium cation additive for stable perovskite solar cells
Publisher: Springer Science and Business Media LLC
Date: 12-2022
DOI: 10.1038/S41563-022-01399-8
Abstract: Achieving the long-term stability of perovskite solar cells is arguably the most important challenge required to enable widespread commercialization. Understanding the perovskite crystallization process and its direct impact on device stability is critical to achieving this goal. The commonly employed dimethyl-formamide/dimethyl-sulfoxide solvent preparation method results in a poor crystal quality and microstructure of the polycrystalline perovskite films. In this work, we introduce a high-temperature dimethyl-sulfoxide-free processing method that utilizes dimethylammonium chloride as an additive to control the perovskite intermediate precursor phases. By controlling the crystallization sequence, we tune the grain size, texturing, orientation (corner-up versus face-up) and crystallinity of the formamidinium (FA)/caesium (FA)
Photoconductive terahertz receivers utilizing single semiconductor nanowires
Publisher: IEEE
Date: 08-2015
Controlling Intrinsic Quantum Confinement in Formamidinium Lead Triiodide Perovskite through Cs Substitution
Publisher: American Chemical Society (ACS)
Date: 24-05-2022
Revealing Ultrafast Charge-Carrier Thermalization in Tin-Iodide Perovskites through Novel Pump–Push–Probe Terahertz Spectroscopy
Publisher: American Chemical Society (ACS)
Date: 09-08-2021
Efficient energy transfer mitigates parasitic light absorption in molecular charge-extraction layers for perovskite solar cells
Publisher: Springer Science and Business Media LLC
Date: 02-11-2020
DOI: 10.1038/S41467-020-19268-W
Abstract: Organic semiconductors are commonly used as charge-extraction layers in metal-halide perovskite solar cells. However, parasitic light absorption in the sun-facing front molecular layer, through which sun light must propagate before reaching the perovskite layer, may lower the power conversion efficiency of such devices. Here, we show that such losses may be eliminated through efficient excitation energy transfer from a photoexcited polymer layer to the underlying perovskite. Experimentally observed energy transfer between a range of different polymer films and a methylammonium lead iodide perovskite layer was used as basis for modelling the efficacy of the mechanism as a function of layer thickness, photoluminescence quantum efficiency and absorption coefficient of the organic polymer film. Our findings reveal that efficient energy transfer can be achieved for thin (≤10 nm) organic charge-extraction layers exhibiting high photoluminescence quantum efficiency. We further explore how the morphology of such thin polymer layers may be affected by interface formation with the perovskite.
Ultrafast Transient Terahertz Conductivity of Monolayer MoS2 and WSe2 Grown by Chemical Vapor Deposition
Publisher: American Chemical Society (ACS)
Date: 04-11-2014
DOI: 10.1021/NN5034746
Abstract: We have measured ultrafast charge carrier dynamics in monolayers and trilayers of the transition metal dichalcogenides MoS2 and WSe2 using a combination of time-resolved photoluminescence and terahertz spectroscopy. We recorded a photoconductivity and photoluminescence response time of just 350 fs from CVD-grown monolayer MoS2, and 1 ps from trilayer MoS2 and monolayer WSe2. Our results indicate the potential of these materials as high-speed optoelectronic materials.
Enhanced UV-light stability of planar heterojunction perovskite solar cells with caesium bromide interface modification
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5EE03522H
Abstract: CsBr interface modification simultaneously enhances the device power conversion efficiency and improves the device resilience to UV irradiation.
Efficient planar heterojunction perovskite solar cells by vapour deposition
Publisher: Springer Science and Business Media LLC
Date: 11-09-2013
DOI: 10.1038/NATURE12509
Abstract: Many different photovoltaic technologies are being developed for large-scale solar energy conversion. The wafer-based first-generation photovoltaic devices have been followed by thin-film solid semiconductor absorber layers sandwiched between two charge-selective contacts and nanostructured (or mesostructured) solar cells that rely on a distributed heterojunction to generate charge and to transport positive and negative charges in spatially separated phases. Although many materials have been used in nanostructured devices, the goal of attaining high-efficiency thin-film solar cells in such a way has yet to be achieved. Organometal halide perovskites have recently emerged as a promising material for high-efficiency nanostructured devices. Here we show that nanostructuring is not necessary to achieve high efficiencies with this material: a simple planar heterojunction solar cell incorporating vapour-deposited perovskite as the absorbing layer can have solar-to-electrical power conversion efficiencies of over 15 per cent (as measured under simulated full sunlight). This demonstrates that perovskite absorbers can function at the highest efficiencies in simplified device architectures, without the need for complex nanostructures.
Narrowband, Angle-Tunable, Helicity-Dependent Terahertz Emission from Nanowires of the Topological Dirac Semimetal Cd3As2
Publisher: American Chemical Society (ACS)
Date: 03-04-2023
Electronic properties of GaAs, InAs and InP nanowires studied by terahertz spectroscopy
Publisher: IOP Publishing
Date: 25-04-2013
DOI: 10.1088/0957-4484/24/21/214006
Abstract: We have performed a comparative study of ultrafast charge carrier dynamics in a range of III-V nanowires using optical pump-terahertz probe spectroscopy. This versatile technique allows measurement of important parameters for device applications, including carrier lifetimes, surface recombination velocities, carrier mobilities and donor doping levels. GaAs, InAs and InP nanowires of varying diameters were measured. For all s les, the electronic response was dominated by a pronounced surface plasmon mode. Of the three nanowire materials, InAs nanowires exhibited the highest electron mobilities of 6000 cm² V⁻¹ s⁻¹, which highlights their potential for high mobility applications, such as field effect transistors. InP nanowires exhibited the longest carrier lifetimes and the lowest surface recombination velocity of 170 cm s⁻¹. This very low surface recombination velocity makes InP nanowires suitable for applications where carrier lifetime is crucial, such as in photovoltaics. In contrast, the carrier lifetimes in GaAs nanowires were extremely short, of the order of picoseconds, due to the high surface recombination velocity, which was measured as 5.4 × 10⁵ cm s⁻¹. These findings will assist in the choice of nanowires for different applications, and identify the challenges in producing nanowires suitable for future electronic and optoelectronic devices.
Conductivity of nanoporous InP membranes investigated using terahertz spectroscopy
Publisher: IOP Publishing
Date: 11-08-2008
DOI: 10.1088/0957-4484/19/39/395704
Abstract: We have investigated the terahertz conductivity of extrinsic and photoexcited electrons in nanoporous indium phosphide (InP) at different pore densities and orientations. The form of electronic transport in the film was found to differ significantly from that for bulk InP. While photo-generated electrons showed Drude-like transport, the behaviour for extrinsic electrons deviated significantly from the Drude model. Time-resolved photoconductivity measurements found that carrier recombination was slow, with lifetimes exceeding 1 ns for all porosities and orientations. When considered together, these findings suggest that the surfaces created by the nanopores strongly alter the dynamics of both extrinsic and photoexcited electrons.
V-grooved GaAs/AlGaAs quantum wires with side wall quantum wells intermixed by pulsed anodization and rapid thermal annealing
Publisher: IEEE
Date: 1996
The influence of surfaces on the transient terahertz conductivity and electron mobility of GaAs nanowires
Publisher: IOP Publishing
Date: 09-05-2017
A low viscosity, low boiling point, clean solvent system for the rapid crystallisation of highly specular perovskite films
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C6EE02373H
Abstract: We present a new solvent system which has the potential to overcome the manufacturing barriers associated with the currently used toxic high boiling point solvents.
Detecting the full polarization state of terahertz transients
Publisher: SPIE
Date: 09-02-2006
DOI: 10.1117/12.660717
Polarization sensitive terahertz time domain spectroscopy
Publisher: IEEE
Date: 2006
Special issue on terahertz science and technology
Publisher: IOP Publishing
Date: 28-08-2014
Optoelectronic Properties of Mixed Iodide–Bromide Perovskites from First-Principles Computational Modeling and Experiment
Publisher: American Chemical Society (ACS)
Date: 05-05-2022
InxGa1−xAs nanowires with uniform composition, pure wurtzite crystal phase and taper-free morphology
Publisher: IOP Publishing
Date: 30-04-2015
DOI: 10.1088/0957-4484/26/20/205604
Abstract: Obtaining compositional homogeneity without compromising morphological or structural quality is one of the biggest challenges in growing ternary alloy compound semiconductor nanowires. Here we report growth of Au-seeded InxGa1-xAs nanowires via metal-organic vapour phase epitaxy with uniform composition, morphology and pure wurtzite (WZ) crystal phase by carefully optimizing growth temperature and V/III ratio. We find that high growth temperatures allow the InxGa1-xAs composition to be more uniform by suppressing the formation of typically observed spontaneous In-rich shells. A low V/III ratio results in the growth of pure WZ phase InxGa1-xAs nanowires with uniform composition and morphology while a high V/III ratio allows pure zinc-blende (ZB) phase to form. Ga incorporation is found to be dependent on the crystal phase favouring higher Ga concentration in ZB phase compared to the WZ phase. Tapering is also found to be more prominent in defective nanowires hence it is critical to maintain the highest crystal structure purity in order to minimize tapering and inhomogeneity. The InP capped pure WZ In0.65Ga0.35As core-shell nanowire heterostructures show 1.54 μm photoluminescence, close to the technologically important optical fibre telecommunication wavelength, which is promising for application in photodetectors and nanoscale lasers.
Increased Photoconductivity Lifetimes in GaAs Nanowires via n-Type and p-Type Shell Doping
Publisher: IEEE
Date: 09-2016
Terahertz Excitonic Response of Isolated Single-Walled Carbon Nanotubes
Publisher: American Chemical Society (ACS)
Date: 17-09-2009
DOI: 10.1021/JP907195T
Single nanowire photoconductive terahertz detectors
Publisher: American Chemical Society (ACS)
Date: 18-12-2015
DOI: 10.1021/NL5033843
Abstract: Spectroscopy and imaging in the terahertz (THz) region of the electromagnetic spectrum has proven to provide important insights in fields as erse as chemical analysis, materials characterization, security screening, and nondestructive testing. However, compact optoelectronics suited to the most powerful terahertz technique, time-domain spectroscopy, are lacking. Here, we implement single GaAs nanowires as microscopic coherent THz sensors and for the first time incorporated them into the pulsed time-domain technique. We also demonstrate the functionality of the single nanowire THz detector as a spectrometer by using it to measure the transmission spectrum of a 290 GHz low pass filter. Thus, nanowires are shown to be well suited for THz device applications and hold particular promise as near-field THz sensors.
Enhanced coherent terahertz emission from indium arsenide in the presence of a magnetic field
Publisher: AIP Publishing
Date: 10-04-2000
DOI: 10.1063/1.126247
Ultrafast photo-induced phonon hardening due to Pauli blocking in MAPbI3 single-crystal and polycrystalline perovskites
Publisher: IOP Publishing
Date: 22-09-2021
Abstract: Metal-halide perovskite semiconductors have attracted intense interest over the past decade, particularly for applications in photovoltaics. Low-energy optical phonons combined with significant crystal anharmonicity play an important role in charge-carrier cooling and scattering in these materials, strongly affecting their optoelectronic properties. We have observed optical phonons associated with Pb–I stretching in both MAPbI 3 single crystals and polycrystalline thin films as a function of temperature by measuring their terahertz conductivity spectra with and without photoexcitation. An anomalous bond hardening was observed under above-bandgap illumination for both single-crystal and polycrystalline MAPbI 3 . First-principles calculations reproduced this photo-induced bond hardening and identified a related lattice contraction (photostriction), with the mechanism revealed as Pauli blocking. For single-crystal MAPbI 3 , phonon lifetimes were significantly longer and phonon frequencies shifted less with temperature, compared with polycrystalline MAPbI 3 . We attribute these differences to increased crystalline disorder, associated with grain boundaries and strain in the polycrystalline MAPbI 3 . Thus we provide fundamental insight into the photoexcitation and electron–phonon coupling in MAPbI 3 .
Optical properties of δ-doped GaAs nipi super-lattices
Publisher: IEEE
Date: 1996
Electron–phonon coupling in hybrid lead halide perovskites
Publisher: Springer Science and Business Media LLC
Date: 26-05-2016
DOI: 10.1038/NCOMMS11755
Abstract: Phonon scattering limits charge-carrier mobilities and governs emission line broadening in hybrid metal halide perovskites. Establishing how charge carriers interact with phonons in these materials is therefore essential for the development of high-efficiency perovskite photovoltaics and low-cost lasers. Here we investigate the temperature dependence of emission line broadening in the four commonly studied formamidinium and methylammonium perovskites, HC(NH 2 ) 2 PbI 3 , HC(NH 2 ) 2 PbBr 3 , CH 3 NH 3 PbI 3 and CH 3 NH 3 PbBr 3 , and discover that scattering from longitudinal optical phonons via the Fröhlich interaction is the dominant source of electron–phonon coupling near room temperature, with scattering off acoustic phonons negligible. We determine energies for the interacting longitudinal optical phonon modes to be 11.5 and 15.3 meV, and Fröhlich coupling constants of ∼40 and 60 meV for the lead iodide and bromide perovskites, respectively. Our findings correlate well with first-principles calculations based on many-body perturbation theory, which underlines the suitability of an electronic band-structure picture for describing charge carriers in hybrid perovskites.
Dynamic terahertz polarization in single-walled carbon nanotubes
Publisher: American Physical Society (APS)
Date: 24-08-2010
Optoelectronic Properties of Tin-Based Hybrid Metal Halide Perovskite Thin Films for Photovoltaics
Publisher: IEEE
Date: 09-2019
Influence of Interface Morphology on Hysteresis in Vapor‐Deposited Perovskite Solar Cells
Publisher: Wiley
Date: 30-12-2016
Ultrafast Charge Separation at a Polymer−Single-Walled Carbon Nanotube Molecular Junction
Publisher: American Chemical Society (ACS)
Date: 24-11-2010
DOI: 10.1021/NL1036484
Abstract: We have investigated the charge photogeneration dynamics at the interface formed between single-walled carbon nanotubes (SWNTs) and poly(3-hexylthiophene) (P3HT) using a combination of femtosecond spectroscopic techniques. We demonstrate that photoexcitation of P3HT forming a single molecular layer around a SWNT leads to an ultrafast (∼430 fs) charge transfer between the materials. The addition of excess P3HT leads to long-term charge separation in which free polarons remain separated at room temperature. Our results suggest that SWNT-P3HT blends incorporating only small fractions (1%) of SWNTs allow photon-to-charge conversion with efficiencies comparable to those for conventional (60:40) P3HT-fullerene blends, provided that small-diameter tubes are in idually embedded in the P3HT matrix.
Effect of Ultraviolet Radiation on Organic Photovoltaic Materials and Devices
Publisher: American Chemical Society (ACS)
Date: 24-05-2019
Intense terahertz generation based on the photo-Dember effect
Publisher: OSA
Date: 2010
High Electron Mobility and Insights into Temperature-Dependent Scattering Mechanisms in InAsSb Nanowires
Publisher: American Chemical Society (ACS)
Date: 02-05-2018
DOI: 10.1021/ACS.NANOLETT.8B00842
Abstract: InAsSb nanowires are promising elements for thermoelectric devices, infrared photodetectors, high-speed transistors, as well as thermophotovoltaic cells. By changing the Sb alloy fraction the mid-infrared bandgap energy and thermal conductivity may be tuned for specific device applications. Using both terahertz and Raman noncontact probes, we show that Sb alloying increases the electron mobility in the nanowires by over a factor of 3 from InAs to InAs
Heterogeneous Photon Recycling and Charge Diffusion Enhance Charge Transport in Quasi-2D Lead-Halide Perovskite Films
Publisher: American Chemical Society (ACS)
Date: 09-05-2019
Ultrafast Terahertz Conductivity Dynamics in Mesoporous TiO2: Influence of Dye Sensitization and Surface Treatment in Solid-State Dye-Sensitized Solar Cells
Publisher: American Chemical Society (ACS)
Date: 21-12-2009
DOI: 10.1021/JP908760R
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University Of Oxford
Location: United Kingdom of Great Britain and Northern Ireland
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Amount: $395,000.00
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Amount: $480,629.00
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View Funded ActivityARC Centres Of Excellence - Grant ID: CE200100010
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End Date: 12-2027
Amount: $34,935,112.00
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View Funded ActivityDiscovery Projects - Grant ID: DP1096754
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View Funded ActivityDiscovery Projects - Grant ID: DP130101743
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End Date: 12-2016
Amount: $400,000.00
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View Funded ActivityDiscovery Projects - Grant ID: DP200103070
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