ORCID Profile
0000-0001-8511-790X
Current Organisation
University of Oxford
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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.
Publisher: Wiley
Date: 09-12-2022
Abstract: Following the 2nd release of the “Emerging PV reports,” the best achievements in the performance of emerging photovoltaic devices in erse emerging photovoltaic research subjects are summarized, as reported in peer‐reviewed articles in academic journals since August 2021. Updated graphs, tables, and analyses are provided with several performance parameters, e.g., power conversion efficiency, open‐circuit voltage, short‐circuit current density, fill factor, light utilization efficiency, and stability test energy yield. These parameters are presented as a function of the photovoltaic bandgap energy and the average visible transmittance for each technology and application, and are put into perspective using, e.g., the detailed balance efficiency limit. The 3rd installment of the “Emerging PV reports” extends the scope toward triple junction solar cells.
Publisher: American Chemical Society (ACS)
Date: 30-03-2021
Publisher: Research Square Platform LLC
Date: 20-01-2023
DOI: 10.21203/RS.3.RS-2495973/V1
Abstract: In the last decade, perovskite semiconductors have triggered a revolution in solar cell research. However, critical issues remain concerning the stability of metal-halide perovskites, which need to be overcome to enable a large scale commercialisation of perovskite photovoltaics (PV). While the rather poor environmental stability of these perovskites is usually attributed to their ionic nature rendering them sensitive to moisture and oxygen, the actual contribution of mobile ions to the total degradation loss under different environmental conditions is poorly understood. In this work, we reveal that the initial degradation of perovskite semiconductors is largely the result of mobile ion-induced internal field screening - a phenomenon that has not been previously discussed in relation to the degradation of perovskite solar cells. The increased field screening leads to a decrease in the steady-state power conversion efficiency mainly due to a large reduction in current density, while the efficiency at high scan speeds ( V/s) where the ions are immobilized is much less affected. We also show that interfacial recombination does not increase upon ageing, yet the open-circuit voltage (VOC) decreases as the result of an increase in the mobile ion density upon ageing. Furthermore, similar ionic losses appear under different external stressors, in particular when there are free charges present in the absorber layer. This work reveals a key degradation mechanism, providing new insights into initial device degradation before chemical or extrinsic mechanical device degradation effects manifest, and it highlights the critical role mobile ions play therein.
Publisher: American Chemical Society (ACS)
Date: 19-03-2014
DOI: 10.1021/JZ500209G
Abstract: Emerging from the field of dye-sensitized solar cells, organometal halide perovskite-based solar cells have recently attracted considerable attention. In these devices, the perovskite light absorbers can also be used as charge transporting materials, changing the requirements for efficient device architectures. The perovskite deposition can vary from merely sensitizing the TiO2 electron transporting scaffold as an endowment of small nanoparticles, to completely filling the pores where it acts as both light absorber and hole transporting material in one. By decreasing the TiO2 scaffold layer thickness, we change the solar cell architecture from perovskite-sensitized to completely perovskite-filled. We find that the latter case leads to improvements in device performance because higher electron densities can be sustained in the TiO2, improving electron transport rates and photovoltage. Importantly, the primary recombination pathway between the TiO2 and the hole transporting material is blocked by the perovskite itself. This understanding helps to rationalize the high voltages attainable on mesoporous TiO2-based perovskite solar cells.
Publisher: Wiley
Date: 20-06-2019
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C3EE43822H
Publisher: Elsevier BV
Date: 10-2017
Publisher: Wiley
Date: 07-06-2023
Abstract: Metal halide perovskite based tandem solar cells are promising to achieve power conversion efficiency beyond the theoretical limit of their single‐junction counterparts. However, overcoming the significant open‐circuit voltage deficit present in wide‐bandgap perovskite solar cells remains a major hurdle for realizing efficient and stable perovskite tandem cells. Here, a holistic approach to overcoming challenges in 1.8 eV perovskite solar cells is reported by engineering the perovskite crystallization pathway by means of chloride additives. In conjunction with employing a self‐assembled monolayer as the hole‐transport layer, an open‐circuit voltage of 1.25 V and a power conversion efficiency of 17.0% are achieved. The key role of methylammonium chloride addition is elucidated in facilitating the growth of a chloride‐rich intermediate phase that directs crystallization of the desired cubic perovskite phase and induces more effective halide homogenization. The as‐formed 1.8 eV perovskite demonstrates suppressed halide segregation and improved optoelectronic 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.
Publisher: Wiley
Date: 15-09-2015
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.
Publisher: American Chemical Society (ACS)
Date: 09-12-2014
DOI: 10.1021/NN505723H
Abstract: Organic-inorganic perovskites, such as CH3NH3PbX3 (X=I, Br, Cl), have emerged as attractive absorber materials for the fabrication of low cost high efficiency solar cells. Over the last 3 years, there has been an exceptional rise in power conversion efficiencies (PCEs), demonstrating the outstanding potential of these perovskite materials. However, in most device architectures, including the simplest thin-film planar structure, a current-voltage response displays an "anomalous hysteresis", whereby the power output of the cell varies with measurement time, direction and light exposure or bias history. Here we provide insight into the physical processes occurring at the interface between the n-type charge collection layer and the perovskite absorber. Through spectroscopic measurements, we find that electron transfer from the perovskite to the TiO2 in the standard planar junction cells is very slow. By modifying the n-type contact with a self-assembled fullerene monolayer, electron transfer is "switched on", and both the n-type and p-type heterojunctions with the perovskite are active in driving the photovoltaic operation. The fullerene-modified devices achieve up to 17.3% power conversion efficiency with significantly reduced hysteresis, and stabilized power output reaching 15.7% in the planar p-i-n heterojunction solar cells measured under simulated AM 1.5 sunlight.
Publisher: Wiley
Date: 20-09-2020
Publisher: IEEE
Date: 06-2018
Publisher: Springer Science and Business Media LLC
Date: 27-06-2014
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8TC00875B
Abstract: The impact of A and X site substitution on acoustic phonon speeds in hybrid perovskites with ABX 3 stoichiometry is studied.
Publisher: American Chemical Society (ACS)
Date: 31-01-2017
DOI: 10.1021/ACS.JPCLETT.6B02682
Abstract: A
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
Publisher: American Chemical Society (ACS)
Date: 08-12-2015
DOI: 10.1021/JACS.5B09085
Abstract: Despite rapid developments in both photovoltaic and light-emitting device performance, the understanding of the optoelectronic properties of hybrid lead halide perovskites is still incomplete. In particular, the polarizability of the material, the presence of molecular dipoles, and their influence on the dynamics of the photoexcitations remain an open issue to be clarified. Here, we investigate the effect of an applied external electric field on the photoexcited species of CH3NH3PbI3 thin films, both at room temperature and at low temperature, by monitoring the photoluminescence (PL) yield and PL decays. At room temperature we find evidence for electric-field-induced reduction of radiative bimolecular carrier recombination together with motion of charged defects that affects the nonradiative decay rate of the photoexcited species. At low temperature (190 K), we observe a field-induced enhancement of radiative free carrier recombination rates that lasts even after the removal of the field. We assign this to field-induced alignment of the molecular dipoles, which reduces the vibrational freedom of the lattice and the associated local screening and hence results in a stronger electron-hole interaction.
Publisher: AIP Publishing
Date: 07-09-2015
DOI: 10.1063/1.4930144
Abstract: Multi-band gap heterojunction solar cells fabricated from a blend of 1.2 eV and 1.4 eV PbS colloidal quantum dots (CQDs) show poor device performance due to non-radiative recombination. To overcome this, a CdS shell is epitaxially formed around the PbS core using cation exchange. From steady state and transient photoluminescence measurements, we understand the nature of charge transfer between these quantum dots. Photoluminescence decay lifetimes are much longer in the PbS/CdS core/shell blend compared to PbS only, explained by a reduction in non-radiative recombination resulting from CdS surface passivation. PbS/CdS heterojunction devices sustain a higher open-circuit voltage and lower reverse saturation current as compared to PbS-only devices, implying lower recombination rates. Further device performance enhancement is attained by modifying the composition profile of the CQD species in the absorbing layer resulting in a three dimensional quantum cascade structure.
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.
Publisher: Wiley
Date: 21-06-2018
Publisher: Springer Science and Business Media LLC
Date: 13-04-2018
DOI: 10.1038/S41598-018-24436-6
Abstract: We explore the degradation behaviour under continuous illumination and direct oxygen exposure of inverted unencapsulated formamidinium(FA) 0.83 Cs 0.17 Pb(I 0.8 Br 0.2 ) 3 , CH 3 NH 3 PbI 3 , and CH 3 NH 3 PbI 3−x Cl x perovskite solar cells. We continuously test the devices in-situ and in-operando with current-voltage sweeps, transient photocurrent, and transient photovoltage measurements, and find that degradation in the CH 3 NH 3 PbI 3−x Cl x solar cells due to oxygen exposure occurs over shorter timescales than FA 0.83 Cs 0.17 Pb(I 0.8 Br 0.2 ) 3 mixed-cation devices. We attribute these oxygen-induced losses in the power conversion efficiencies to the formation of electron traps within the perovskite photoactive layer. Our results highlight that the formamidinium-caesium mixed-cation perovskites are much less sensitive to oxygen-induced degradation than the methylammonium-based perovskite cells, and that further improvements in perovskite solar cell stability should focus on the mitigation of trap generation during ageing.
Publisher: American Physical Society (APS)
Date: 11-09-2014
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
Publisher: American Chemical Society (ACS)
Date: 07-2014
DOI: 10.1021/NN502115K
Abstract: Solution-processed organometal trihalide perovskite solar cells are attracting increasing interest, leading to high performances over 15% in thin film architectures. Here, we probe the presence of sub gap states in both solid and mesosuperstructured perovskite films and determine that they strongly influence the photoconductivity response and splitting of the quasi-Fermi levels in films and solar cells. We find that while the planar perovskite films are superior to the mesosuperstructured films in terms of charge carrier mobility (in excess of 20 cm(2) V(-1) s(-1)) and emissivity, the planar heterojunction solar cells are limited in photovoltage by the presence of sub gap states and low intrinsic doping densities.
Publisher: American Chemical Society (ACS)
Date: 10-06-2015
Abstract: We have employed soft and hard X-ray photoelectron spectroscopies to study the depth-dependent chemical composition of mixed-halide perovskite thin films used in high-performance solar cells. We detect substantial amounts of metallic lead in the perovskite films, which correlate with significant density of states above the valence band maximum. The metallic lead content is higher in the bulk of the perovskite films than at the surface. Using an optimized postanneal process in air, we can reduce the metallic lead content in the perovskite film. This process reduces the amount of metallic lead and a corresponding increase in the photoluminescence quantum efficiency of the perovskite films can be observed. This correlation indicates that metallic lead impurities are likely a key defect whose concentration can be controlled by simple annealing procedures in order to increase the performance for perovskite solar cells.
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5EE02925B
Abstract: We report optical measurements on MAPbI 3 solar cells, together with ab initio simulations, to investigate the material property changes across the tetragonal to cubic phase transition.
Publisher: American Chemical Society (ACS)
Date: 21-09-2023
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.
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2EE22320A
Publisher: Wiley
Date: 17-09-2018
Abstract: Optoelectronic properties are unraveled for formamidinium tin triiodide (FASnI
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.
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
Publisher: Springer Science and Business Media LLC
Date: 15-06-2015
DOI: 10.1038/NPHYS3357
Publisher: American Association for the Advancement of Science (AAAS)
Date: 08-05-2015
Abstract: Great strides have been made in improving the efficiency of organic-inorganic perovskite solar cells. Further improvements are likely to depend on understanding the role of film morphology on charge-carrier dynamics. de Quilettes et al. correlated confocal fluorescence microscopy images with those from scanning electron microscopy to spatially resolve the photoluminescence and carrier decay dynamics from films of organic-inorganic perovskites. Carrier lifetimes varied widely even between grains, and chemical treatments could improve lifetimes Science , this issue p. 683
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6EE01514J
Abstract: This review article explores the historical development and the recent progress of photoelectrochromic devices (PECDs), evaluating on the bases of components evolution their future perspectives.
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.
Publisher: Springer Science and Business Media LLC
Date: 13-08-2018
Publisher: Wiley
Date: 05-06-2017
Publisher: AIP Publishing
Date: 28-07-2014
DOI: 10.1063/1.4889845
Abstract: We have fabricated CH3NH3PbI3−xClx perovskite thin films crystallized in situ on substrates of different natures (e.g., porosity, wettability) and investigated their photoluminescence properties. We observe that the crystallization time and thin film structure are strongly influenced by the chemical nature and porosity of the substrate. Moreover, we find that the mesoporous scaffold can tune the emissive properties of the semiconducting compound both in terms of spectral region and dynamics. In particular, perovskite crystallites grown in the nanometre size porous scaffold present a shorter-living and blue-shifted emission with respect to the perovskite crystals which are free to grow without any constraints.
Publisher: Elsevier BV
Date: 05-2017
Publisher: American Chemical Society (ACS)
Date: 25-06-2013
DOI: 10.1021/NL401044Q
Abstract: A plethora of solution-processed materials have been developed for solar cell applications. Hybrid solar cells based on light absorbing semiconducting polymers infiltrated into mesoporous TiO2 are an interesting concept, but generating charge at the polymer-metal oxide heterojunction is challenging. Metal-organic perovskite absorbers have recently shown remarkable efficiencies but currently lack the range of color tunability of organics. Here, we have combined a fullerene self-assembled monolayer (C60SAM) functionalized mesoporous titania, a perovskite absorber (CH3NH3PbI3-xClx), and a light absorbing polymer hole-conductor, P3HT, to realize a 6.7% efficient hybrid solar cell. We find that photoexcitations in both the perovskite and the polymer undergo very efficient electron transfer to the C60SAM. The C60SAM acts as an electron acceptor but inhibits further electron transfer into the TiO2 mesostructure due to energy level misalignment and poor electronic coupling. Thermalized electrons from the C60SAM are then transported through the perovskite phase. This strategy allows a reduction of energy loss, while still employing a "mesoporous electron acceptor", representing an exciting and versatile route forward for hybrid photovoltaics incorporating light-absorbing polymers. Finally, we show that we can use the C60SAM functionalization of mesoporous TiO2 to achieve an 11.7% perovskite-sensitized solar cell using Spiro-OMeTAD as a transparent hole transporter.
Publisher: Wiley
Date: 04-08-2017
Publisher: Wiley
Date: 20-08-2020
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
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
Publisher: Wiley
Date: 08-07-2015
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C6EE03201J
Abstract: Mixed-metal compositional screening identifies Co 2+ as capable of partial B-site substitution in CH 3 NH 3 PbI 3 , which supplies new dimensions of material tunability.
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.
Publisher: Wiley
Date: 02-02-2016
Publisher: American Chemical Society (ACS)
Date: 02-2021
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.
Publisher: Wiley
Date: 03-02-2020
Publisher: Wiley
Date: 12-09-2021
Abstract: Organometal perovskite single crystals have been recognized as a promising platform for high‐performance optoelectronic devices, featuring high crystallinity and stability. However, a high trap density and structural nonuniformity at the surface have been major barriers to the progress of single crystal‐based optoelectronic devices. Here, the formation of a unique nanoisland structure is reported at the surface of the facet‐controlled cuboid MAPbI 3 (MA = CH 3 NH 3 + ) single crystals through a cation interdiffusion process enabled by energetically vaporized CsI. The interdiffusion of mobile ions between the bulk and the surface is triggered by thermally activated CsI vapor, which reconstructs the surface that is rich in MA and CsI with reduced dangling bonds. Simultaneously, an array of Cs‐Pb‐rich nanoislands is constructed on the surface of the MAPbI 3 single crystals. This newly reconstructed nanoisland surface enhances the light absorbance over 50% and increases the charge carrier mobility from 56 to 93 cm 2 V −1 s −1 . As confirmed by Kelvin probe force microscopy, the nanoislands form a gradient band bending that prevents recombination of excess carriers, and thus, enhances lateral carrier transport properties. This unique engineering of the single crystal surface provides a pathway towards developing high‐quality perovskite single‐crystal surface for optoelectronic applications.
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D1TA08756H
Abstract: The surface passivating and defect suppressing nature of Cd dopants and DDAB ligands in PNCs provides remarkable photoluminescence quantum yield and emission stability, leading to enhanced device efficiencies in blue PeLEDs.
Publisher: American Chemical Society (ACS)
Date: 19-08-2013
DOI: 10.1021/NL4024287
Abstract: Recently, inorganic and hybrid light absorbers such as quantum dots and organometal halide perovskites have been studied and applied in fabricating thin-film photovoltaic devices because of their low-cost and potential for high efficiency. Further boosting the performance of solution processed thin-film solar cells without detrimentally increasing the complexity of the device architecture is critically important for commercialization. Here, we demonstrate photocurrent and efficiency enhancement in meso-superstructured organometal halide perovskite solar cells incorporating core-shell Au@SiO2 nanoparticles (NPs) delivering a device efficiency of up to 11.4%. We attribute the origin of enhanced photocurrent to a previously unobserved and unexpected mechanism of reduced exciton binding energy with the incorporation of the metal nanoparticles, rather than enhanced light absorption. Our findings represent a new aspect and lever for the application of metal nanoparticles in photovoltaics and could lead to facile tuning of exciton binding energies in perovskite semiconductors.
Publisher: American Chemical Society (ACS)
Date: 10-2020
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.
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
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.
Publisher: Wiley
Date: 06-02-2015
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.
Publisher: American Chemical Society (ACS)
Date: 07-04-2021
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.
Publisher: Springer Science and Business Media LLC
Date: 05-2015
Abstract: Metal-halide perovskites are crystalline materials originally developed out of scientific curiosity. Unexpectedly, solar cells incorporating these perovskites are rapidly emerging as serious contenders to rival the leading photovoltaic technologies. Power conversion efficiencies have jumped from 3% to over 20% in just four years of academic research. Here, we review the rapid progress in perovskite solar cells, as well as their promising use in light-emitting devices. In particular, we describe the broad tunability and fabrication methods of these materials, the current understanding of the operation of state-of-the-art solar cells and we highlight the properties that have delivered light-emitting diodes and lasers. We discuss key thermal and operational stability challenges facing perovskites, and give an outlook of future research avenues that might bring perovskite technology to commercialization.
Publisher: American Chemical Society (ACS)
Date: 21-04-2015
Publisher: American Chemical Society (ACS)
Date: 30-04-2018
Publisher: AIP Publishing
Date: 10-2009
DOI: 10.1063/1.3204982
Abstract: The efficiency of a photovoltaic device is limited by the portion of solar energy that can be captured. We discuss how to measure the optical properties of the various layers in solid-state dye-sensitized solar cells (SDSC). We use spectroscopic ellipsometry to determine the complex refractive index of each of the various layers in a SDSC. Each of the ellipsometry fits is used to calculate a transmission spectrum that is compared to a measured transmission spectrum. The complexities of pore filling on the fitting of the ellipsometric data are discussed. Scanning electron microscopy and energy dispersive x-ray spectroscopy is shown to be an effective method for determining pore filling in SDSC layers. Accurate effective medium optical constants for each layer are presented and the material limits under which these optical constants can be used are discussed.
Publisher: American Chemical Society (ACS)
Date: 04-02-2020
Publisher: American Chemical Society (ACS)
Date: 17-07-2019
Publisher: American Chemical Society (ACS)
Date: 10-05-2023
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.
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.
Publisher: American Chemical Society (ACS)
Date: 28-04-2023
DOI: 10.1021/JACS.3C01531
Publisher: American Chemical Society (ACS)
Date: 17-06-2014
DOI: 10.1021/CM501595U
Publisher: Wiley
Date: 30-05-2014
Publisher: American Chemical Society (ACS)
Date: 17-04-2020
Publisher: Springer Science and Business Media LLC
Date: 24-05-2016
DOI: 10.1038/NCOMMS11683
Abstract: Organic–inorganic perovskites such as CH 3 NH 3 PbI 3 are promising materials for a variety of optoelectronic applications, with certified power conversion efficiencies in solar cells already exceeding 21%. Nevertheless, state-of-the-art films still contain performance-limiting non-radiative recombination sites and exhibit a range of complex dynamic phenomena under illumination that remain poorly understood. Here we use a unique combination of confocal photoluminescence (PL) microscopy and chemical imaging to correlate the local changes in photophysics with composition in CH 3 NH 3 PbI 3 films under illumination. We demonstrate that the photo-induced ‘brightening’ of the perovskite PL can be attributed to an order-of-magnitude reduction in trap state density. By imaging the same regions with time-of-flight secondary-ion-mass spectrometry, we correlate this photobrightening with a net migration of iodine. Our work provides visual evidence for photo-induced halide migration in triiodide perovskites and reveals the complex interplay between charge carrier populations, electronic traps and mobile halides that collectively impact optoelectronic performance.
Publisher: American Chemical Society (ACS)
Date: 02-08-2017
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.
Publisher: American Chemical Society (ACS)
Date: 07-05-2014
DOI: 10.1021/NL500627X
Abstract: Organic-inorganic halide perovskites, such as CH3NH3PbX3 (X = I(-), Br(-), Cl(-)), are attracting growing interest to prepare low-cost solar cells that are capable of converting sunlight to electricity at the highest efficiencies. Despite negligible effort on enhancing materials' purity or passivation of surfaces, high efficiencies have already been achieved. Here, we show that trap states at the perovskite surface generate charge accumulation and consequent recombination losses in working solar cells. We identify that undercoordinated iodine ions within the perovskite structure are responsible and make use of supramolecular halogen bond complexation to successfully passivate these sites. Following this strategy, we demonstrate solar cells with maximum power conversion efficiency of 15.7% and stable power output over 15% under constant 0.81 V forward bias in simulated full sunlight. The surface passivation introduces an important direction for future progress in perovskite solar cells.
Publisher: Springer Science and Business Media LLC
Date: 30-01-2015
DOI: 10.1038/NCOMMS7142
Abstract: To date, there have been a plethora of reports on different means to fabricate organic-inorganic metal halide perovskite thin films however, the inorganic starting materials have been limited to halide-based anions. Here we study the role of the anions in the perovskite solution and their influence upon perovskite crystal growth, film formation and device performance. We find that by using a non-halide lead source (lead acetate) instead of lead chloride or iodide, the perovskite crystal growth is much faster, which allows us to obtain ultrasmooth and almost pinhole-free perovskite films by a simple one-step solution coating with only a few minutes annealing. This synthesis leads to improved device performance in planar heterojunction architectures and answers a critical question as to the role of the anion and excess organic component during crystallization. Our work paves the way to tune the crystal growth kinetics by simple chemistry.
Publisher: American Chemical Society (ACS)
Date: 02-04-2014
DOI: 10.1021/JZ5005285
Abstract: The study of the photophysical properties of organic-metallic lead halide perovskites, which demonstrate excellent photovoltaic performance in devices with electron- and hole-accepting layers, helps to understand their charge photogeneration and recombination mechanism and unravels their potential for other optoelectronic applications. We report surprisingly high photoluminescence (PL) quantum efficiencies, up to 70%, in these solution-processed crystalline films. We find that photoexcitation in the pristine CH3NH3PbI3-xClx perovskite results in free charge carrier formation within 1 ps and that these free charge carriers undergo bimolecular recombination on time scales of 10s to 100s of ns. To exemplify the high luminescence yield of the CH3NH3PbI3-xClx perovskite, we construct and demonstrate the operation of an optically pumped vertical cavity laser comprising a layer of perovskite between a dielectric mirror and evaporated gold top mirrors. These long carrier lifetimes together with exceptionally high luminescence yield are unprecedented in such simply prepared inorganic semiconductors, and we note that these properties are ideally suited for photovoltaic diode operation.
Publisher: Wiley
Date: 11-11-2021
Abstract: Following the 1st release of the “Emerging photovoltaic (PV) reports” , the best achievements in the performance of emerging photovoltaic devices in erse emerging photovoltaic research subjects are summarized, as reported in peer‐reviewed articles in academic journals since August 2020. Updated graphs, tables, and analyses are provided with several performance parameters, e.g., power conversion efficiency, open‐circuit voltage, short‐circuit current density, fill factor, light utilization efficiency, and stability test energy yield. These parameters are presented as a function of the photovoltaic bandgap energy and the average visible transmittance for each technology and application and are put into perspective using, e.g., the detailed balance efficiency limit. The 2nd instalment of the “Emerging PV reports” extends the scope toward tandem solar cells and presents the current state‐of‐the‐art in tandem solar cell performance for various material combinations.
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.
Publisher: AIP Publishing
Date: 10-2009
DOI: 10.1063/1.3204985
Abstract: We use the optical transfer-matrix method to quantify the spatial distribution of light in solid-state dye-sensitized solar cells (DSCs), employing material optical properties measured experimentally in the accompanying article (Part I) as input into the optical model. By comparing the optical modeling results with experimental photovoltaic action spectra for solid-state DSCs containing either a ruthenium-based dye or an organic indoline-based dye, we show that the internal quantum efficiency (IQE) of the devices for both dyes is around 60% for almost all wavelengths, substantially lower than the almost 100% IQE measured for liquid DSCs, indicating substantial electrical losses in solid-state DSCs that can account for much of the current factor-of-two difference between the efficiencies of liquid and solid-state DSCs. The model calculations also demonstrate significant optical losses due to absorption by 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9′-spirobifluorene (spiro-OMeTAD) and TiO2 in the blue and to a lesser extent throughout the visible. As a consequence, the more absorptive organic dye, D149, should outperform the standard ruthenium complex sensitizer, Z907, for all device thicknesses, underlining the potential benefits of high extinction coefficient dyes optimized for solid-state DSC operation.
Publisher: American Physical Society (APS)
Date: 06-01-2021
Publisher: American Chemical Society (ACS)
Date: 27-11-2018
Publisher: Wiley
Date: 20-12-2013
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D1CC00060H
Abstract: We developed a high-performance hole transport material based on transition metal complexes for perovskite solar cells, which exhibits excellent photostability.
Publisher: American Chemical Society (ACS)
Date: 20-09-2013
DOI: 10.1021/JP405734F
Publisher: Wiley
Date: 30-05-2014
Publisher: Wiley
Date: 04-12-2020
Publisher: American Chemical Society (ACS)
Date: 06-12-2017
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.
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%.
Publisher: American Chemical Society (ACS)
Date: 10-10-2019
Publisher: Springer Science and Business Media LLC
Date: 06-08-2018
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
Publisher: Elsevier BV
Date: 02-2019
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.
Publisher: Wiley
Date: 16-08-2019
Publisher: American Chemical Society (ACS)
Date: 19-11-2015
Publisher: Springer Science and Business Media LLC
Date: 16-06-2015
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.
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.
Publisher: American Chemical Society (ACS)
Date: 13-02-2015
DOI: 10.1021/NL504349Z
Publisher: American Chemical Society (ACS)
Date: 23-12-2022
Publisher: Wiley
Date: 30-01-2020
Publisher: American Chemical Society (ACS)
Date: 06-03-2015
DOI: 10.1021/NN506465N
Abstract: Recently, solution-processable organic-inorganic metal halide perovskites have come to the fore as a result of their high power-conversion efficiencies (PCE) in photovoltaics, exceeding 17%. To attain reproducibility in the performance, one of the critical factors is the processing conditions of the perovskite film, which directly influences the photophysical properties and hence the device performance. Here we study the effect of annealing parameters on the crystal structure of the perovskite films and correlate these changes with its photophysical properties. We find that the crystal formation is kinetically driven by the annealing atmosphere, time and temperature. Annealing in air produces an improved crystallinity and large grain domains as compared to nitrogen. Lower photoluminescence quantum efficiency (PLQE) and shorter photoluminescence (PL) lifetimes are observed for nitrogen annealed perovskite films as compared to the air-annealed counterparts. We note that the limiting nonradiative pathways (i.e., maximizing PLQE) is important for obtaining the highest device efficiency. This indicates a critical impact of the atmosphere upon crystallization and the ultimate device performance.
Publisher: IEEE
Date: 09-2013
Publisher: Wiley
Date: 02-2018
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.
Publisher: American Chemical Society (ACS)
Date: 21-08-2019
Publisher: Springer Science and Business Media LLC
Date: 07-2019
DOI: 10.1038/S41586-019-1357-2
Abstract: Solar cells based on metal halide perovskites are one of the most promising photovoltaic technologies
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5EE03435C
Abstract: The reduced effective mass ( μ ) and excitonic Rydberg ( R *) are measured by magneto-optics for new perovskite semiconductors.
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)
Publisher: American Chemical Society (ACS)
Date: 25-08-2018
Publisher: Wiley
Date: 05-03-2020
Publisher: American Chemical Society (ACS)
Date: 09-08-2021
Publisher: American Chemical Society (ACS)
Date: 14-11-2017
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6EE01504B
Abstract: The photoinduced removal of trap states due to Frenkel defects is found to enhance the PLQE of perovskite thin films.
Publisher: American Chemical Society (ACS)
Date: 10-04-2014
DOI: 10.1021/JZ500113X
Abstract: Perovskite solar cells have rapidly risen to the forefront of emerging photovoltaic technologies, exhibiting rapidly rising efficiencies. This is likely to continue to rise, but in the development of these solar cells there are unusual characteristics that have arisen, specifically an anomalous hysteresis in the current-voltage curves. We identify this phenomenon and show some ex les of factors that make the hysteresis more or less extreme. We also demonstrate stabilized power output under working conditions and suggest that this is a useful parameter to present, alongside the current-voltage scan derived power conversion efficiency. We hypothesize three possible origins of the effect and discuss its implications on device efficiency and future research directions. Understanding and resolving the hysteresis is essential for further progress and is likely to lead to a further step improvement in performance.
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.
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C7EE03013D
Abstract: Simultaneous GI-WAXS diffraction patterns and JV measurement of IBC solar cells during in situ anneal.
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.
Publisher: Springer Science and Business Media LLC
Date: 08-04-2014
DOI: 10.1038/NCOMMS4586
Abstract: Excitonic solar cells, within which bound electron-hole pairs have a central role in energy harvesting, have represented a hot field of research over the last two decades due to the compelling prospect of low-cost solar energy. However, in such cells, exciton dissociation and charge collection occur with significant losses in energy, essentially due to poor charge screening. Organic-inorganic perovskites show promise for overcoming such limitations. Here, we use optical spectroscopy to estimate the exciton binding energy in the mixed-halide crystal to be in the range of 50 meV. We show that such a value is consistent with almost full ionization of the exciton population under photovoltaic cell operating conditions. However, increasing the total photoexcitation density, excitonic species become dominant, widening the perspective of this material for a host of optoelectronic applications.
Publisher: AIP Publishing
Date: 14-03-2016
DOI: 10.1063/1.4944044
Abstract: Time-delayed collection field experiments are applied to planar organometal halide perovskite (CH3NH3PbI3) based solar cells to investigate charge carrier recombination in a fully working solar cell at the nanosecond to microsecond time scale. Recombination of mobile (extractable) charges is shown to follow second-order recombination dynamics for all fluences and time scales tested. Most importantly, the bimolecular recombination coefficient is found to be time-dependent, with an initial value of ca. 10−9 cm3/s and a progressive reduction within the first tens of nanoseconds. Comparison to the prototypical organic bulk heterojunction device PTB7:PC71BM yields important differences with regard to the mechanism and time scale of free carrier recombination.
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6TA01087C
Abstract: We investigate the influence of solvent drenching in hybrid organic–inorganic perovskite (CH 3 NH 3 PbX) crystallization process with a non-solvent, toluene, during film fabrication process.
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.
Publisher: American Chemical Society (ACS)
Date: 11-2011
DOI: 10.1021/JP207075Z
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.
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.
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.
Publisher: American Chemical Society (ACS)
Date: 15-09-2014
DOI: 10.1021/NN5036476
Abstract: Organic-inorganic metal halide perovskites have recently emerged as a top contender to be used as an absorber material in highly efficient, low-cost photovoltaic devices. Solution-processed semiconductors tend to have a high density of defect states and exhibit a large degree of electronic disorder. Perovskites appear to go against this trend, and despite relatively little knowledge of the impact of electronic defects, certified solar-to-electrical power conversion efficiencies of up to 17.9% have been achieved. Here, through treatment of the crystal surfaces with the Lewis bases thiophene and pyridine, we demonstrate significantly reduced nonradiative electron-hole recombination within the CH(3)NH(3)PbI(3-x)Cl(x) perovskite, achieving photoluminescence lifetimes which are enhanced by nearly an order of magnitude, up to 2 μs. We propose that this is due to the electronic passivation of under-coordinated Pb atoms within the crystal. Through this method of Lewis base passivation, we achieve power conversion efficiencies for solution-processed planar heterojunction solar cells enhanced from 13% for the untreated solar cells to 15.3% and 16.5% for the thiophene and pyridine-treated solar cells, respectively.
Publisher: American Chemical Society (ACS)
Date: 05-05-2022
Publisher: American Chemical Society (ACS)
Date: 09-05-2022
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.
Publisher: Springer Science and Business Media LLC
Date: 10-11-2016
DOI: 10.1038/NCOMMS13303
Abstract: Optoelectronic devices based on hybrid halide perovskites have shown remarkable progress to high performance. However, despite their apparent success, there remain many open questions about their intrinsic properties. Single crystals are often seen as the ideal platform for understanding the limits of crystalline materials, and recent reports of rapid, high-temperature crystallization of single crystals should enable a variety of studies. Here we explore the mechanism of this crystallization and find that it is due to reversible changes in the solution where breaking up of colloids, and a change in the solvent strength, leads to supersaturation and subsequent crystallization. We use this knowledge to demonstrate a broader range of processing parameters and show that these can lead to improved crystal quality. Our findings are therefore of central importance to enable the continued advancement of perovskite optoelectronics and to the improved reproducibility through a better understanding of factors influencing and controlling crystallization.
Publisher: American Chemical Society (ACS)
Date: 22-09-2014
DOI: 10.1021/NL501982B
Abstract: Organic-inorganic perovskite solar cells have recently emerged at the forefront of photovoltaics research. Power conversion efficiencies have experienced an unprecedented increase to reported values exceeding 19% within just four years. With the focus mainly on efficiency, the aspect of stability has so far not been thoroughly addressed. In this paper, we identify thermal stability as a fundamental weak point of perovskite solar cells, and demonstrate an elegant approach to mitigating thermal degradation by replacing the organic hole transport material with polymer-functionalized single-walled carbon nanotubes (SWNTs) embedded in an insulating polymer matrix. With this composite structure, we achieve JV scanned power-conversion efficiencies of up to 15.3% with an average efficiency of 10 ± 2%. Moreover, we observe strong retardation in thermal degradation as compared to cells employing state-of-the-art organic hole-transporting materials. In addition, the resistance to water ingress is remarkably enhanced. These are critical developments for achieving long-term stability of high-efficiency perovskite solar cells.
Publisher: Wiley
Date: 30-12-2016
Publisher: Springer Science and Business Media LLC
Date: 22-01-2020
DOI: 10.1038/S41560-019-0529-5
Abstract: Improving the long-term stability of perovskite solar cells is critical to the deployment of this technology. Despite the great emphasis laid on stability-related investigations, publications lack consistency in experimental procedures and parameters reported. It is therefore challenging to reproduce and compare results and thereby develop a deep understanding of degradation mechanisms. Here, we report a consensus between researchers in the field on procedures for testing perovskite solar cell stability, which are based on the International Summit on Organic Photovoltaic Stability (ISOS) protocols. We propose additional procedures to account for properties specific to PSCs such as ion redistribution under electric fields, reversible degradation and to distinguish ambient-induced degradation from other stress factors. These protocols are not intended as a replacement of the existing qualification standards, but rather they aim to unify the stability assessment and to understand failure modes. Finally, we identify key procedural information which we suggest reporting in publications to improve reproducibility and enable large data set analysis.
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D3EE00952A
Abstract: This review details the design considerations for the bottom silicon cell in perovskite/silicon tandems. The review highlights the shift in mindset required when transitioning to the mass production of tandem solar cells.
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.
Publisher: American Chemical Society (ACS)
Date: 20-11-2014
DOI: 10.1021/JZ5021795
Abstract: Here, we report the use of polymer-wrapped carbon nanotubes as a means to enhance charge extraction through undoped spiro-OMeTAD. With this approach a good solar cell performance is achieved without the implementation of conventional doping methods. We demonstrate that a stratified two-layer architecture of sequentially deposited layers of carbon nanotubes and spiro-OMeTAD, outperforms a conventional blend of the hole-conductor and the carbon nanotubes. We also provide insights into the mechanism of the rapid hole extraction observed in the two-layer approach.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 18-10-2013
Abstract: In the past 2 years, organolead halide perovskites have emerged as a promising class of light-harvesting media in experimental solar cells, but the physical basis for their efficiency has been unclear (see the Perspective by Hodes ). Two studies now show, using a variety of time-resolved absorption and emission spectroscopic techniques, that these materials manifest relatively long diffusion paths for charge carriers energized by light absorption. Xing et al. (p. 344 ) independently assessed (negative) electron and (positive) hole diffusion lengths and found them well-matched to one another to the ~100-nanometer optical absorption depth. Stranks et al. (p. 341 ) uncovered a 10-fold greater diffusion length in a chloride-doped material, which correlates with the material's particularly efficient overall performance. Both studies highlight effective carrier diffusion as a fruitful parameter for further optimization.
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9TA08351K
Abstract: A facile bulk recrystallization process remove excess PbI 2 and improved the performance in perovskite solar cells.
Publisher: American Chemical Society (ACS)
Date: 21-12-2009
DOI: 10.1021/JP908760R
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Henry Snaith.