ORCID Profile
0000-0001-5132-1232
Current Organisations
King's College London
,
University of Oxford
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: Wiley
Date: 05-03-2020
Publisher: American Chemical Society (ACS)
Date: 14-11-2017
Publisher: Wiley
Date: 02-02-2016
Publisher: American Chemical Society (ACS)
Date: 02-2021
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.
Publisher: American Chemical Society (ACS)
Date: 06-11-2015
Publisher: Wiley
Date: 03-02-2020
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
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.
Publisher: American Chemical Society (ACS)
Date: 18-10-2023
Publisher: Wiley
Date: 20-06-2019
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: IEEE
Date: 09-2019
Publisher: Elsevier BV
Date: 10-2017
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: 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: 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: 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: 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: Springer Science and Business Media LLC
Date: 13-09-2018
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: 06-04-2021
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.
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: 30-04-2018
Publisher: American Chemical Society (ACS)
Date: 04-02-2020
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
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: Wiley
Date: 30-01-2020
Publisher: American Chemical Society (ACS)
Date: 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: Wiley
Date: 29-05-2023
Abstract: Metal halide perovskites have recently emerged as exceptional scintillator materials for ionizing radiation detection devices. Their chemical composition consists of elements with high atomic numbers, leading them to have a high attenuation coefficient. Their high attenuation coefficient, in combination with their excellent optoelectronic properties, versatile chemical tunability, and facile and low‐cost fabrication processes, makes them the ideal scintillator material. However, existing perovskite‐based scintillators suffer from poor material stability, especially in humid atmospheres. Moreover, current perovskite films have morphologies that have been optimized for photovoltaics, which results in the relatively long charge carrier lifetimes, a property that is detrimental for fast scintillation. Furthermore, existing reports of perovskite‐based scintillators have shown limited spatial resolution due to poor light transmittance that arises from light scattering from large aggregates of perovskite grains. To address these issues, this work introduces a template‐assisted in situ polymerization‐based process to prepare perovskite olymer composite scintillators that simultaneously reduces afterglow effects, improves perovskite stability, and is industrially scalable. The optimized perovskite scintillators are then incorporated into X‐ray detection devices to investigate detection performance and device stability. Compared with existing commercial scintillators, the perovskite scintillators show superior detection performance metrics for imaging, indicating the great potential of perovskites for next‐generation, large‐area, and flexible scintillation screens.
Publisher: American Chemical Society (ACS)
Date: 09-05-2022
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.
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: Wiley
Date: 30-12-2016
Publisher: American Chemical Society (ACS)
Date: 24-05-2019
Publisher: Wiley
Date: 04-08-2017
Publisher: American Chemical Society (ACS)
Date: 27-11-2018
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United States of America
No related grants have been discovered for Jay Patel.