The Experts below are selected from a list of 8412 Experts worldwide ranked by ideXlab platform
Yi Zhang - One of the best experts on this subject based on the ideXlab platform.
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auto passivation of crystal Defects in hybrid imidazolium methylammonium lead iodide films by fumigation with methylamine affords high efficiency perovskite solar cells
Nano Energy, 2019Co-Authors: Yi Zhang, Giulia Grancini, Zhaofu Fei, Erfan Shirzadi, Xuehui Liu, Emad Oveisi, Farzaneh Fadaei Tirani, Rosario Scopelliti, Yaqing FengAbstract:Abstract Hybrid perovskite solar cells have attracted tremendous interest in the photovoltaic community. Despite their high Defect Tolerance, reducing the trap density by material engineering and surface modification is still critical to further boost performance. Here, methylammonium lead(II) iodide perovskite has been doped with imidazolium iodide in high concentrations (10–30 mol%) to boost solar cell performance, by passivating Defects. Fumigation with methylamine results in the deprotonation of the embedded imidazolium cations, generating imidazole and methylammonium cations. The resulting (neutral) imidazole is extruded from the 3-D perovskite crystal and distributes around the crystal leading to auto-passivation of crystal Defects. The structure of the imidazolium-PbI3 salt intermediate (i.e. formed in the absence of the methylammonium cation) has been determined and the resulting perovskite film characterized. Employed in solar cells, a power conversion efficiency (PCE) up to 20.14% is demonstrated.
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Auto-passivation of crystal Defects in hybrid imidazolium/methylammonium lead iodide films by fumigation with methylamine affords high efficiency perovskite solar cells
'Elsevier BV', 2019Co-Authors: Yi Zhang, Grancini Giulia, Fei Zhaofu, Shirzadi Erfan, Liu Xuehui, Oveisi Emad, Tirani, Farzaneh Fadaei, Scopelliti Rosario, Feng Yaqing, Nazeeruddin, Mohammad KhajaAbstract:Hybrid perovskite solar cells have attracted tremendous interest in the photovoltaic community. Despite their high Defect Tolerance, reducing the trap density by material engineering and surface modification is still critical to further boost performance. Here, methylammonium lead(II) iodide perovskite has been doped with imidazolium iodide in high concentrations (10-30 mol%) to boost solar cell performance, by passivating Defects. Fumigation with methylamine results in the deprotonation of the embedded imidazolium cations, generating imidazole and methylammonium cations. The resulting (neutral) imidazole is extruded from the 3-D perovskite crystal and distributes around the crystal leading to auto-passivation of crystal Defects. The structure of the imidazolium-PbI3 salt intermediate (i.e. formed in the absence of the methylammonium cation) has been determined and the resulting perovskite film characterized. Employed in solar cells, a power conversion efficiency (PCE) up to 20.14% is demonstrated
Vladan Stevanovic - One of the best experts on this subject based on the ideXlab platform.
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structural and chemical features giving rise to Defect Tolerance of binary semiconductors
Chemistry of Materials, 2018Co-Authors: Rachel C Kurchin, Vladan Stevanovic, Tonio Buonassisi, Prashun GoraiAbstract:Defect Tolerance, or the resilience of electronic transport properties of a crystalline material to the presence of Defects, has emerged as a critical factor in the success of hybrid lead halide perovskites as photovoltaic absorbers. A key aspect of Defect Tolerance is the shallow character of dominant intrinsic Defects. However, while qualitative heuristics to identify other Defect-tolerant materials have been proposed, in particular, the presence of a partially oxidized ns2 cation such as Pb, no compelling comprehensive understanding of how these shallow Defects arise has yet emerged. Using modern Defect theory and Defect calculations, we conduct a detailed investigation of the mechanisms and identify specific features related to the chemical composition and crystal structure that give rise to Defect Tolerance. We find that an ns2 cation is necessary but not sufficient to guarantee shallow cation vacancies in an s–p system, and that a compound’s crystal structure can ensure shallow anion vacancies in a ...
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Defect Tolerance in methylammonium lead triiodide perovskite
ACS energy letters, 2016Co-Authors: Xerxes K Steirer, Philip Schulz, Glenn Teeter, Vladan Stevanovic, Mengjin Yang, Joseph J BerryAbstract:Photovoltaic applications of perovskite semiconductor material systems have generated considerable interest in part because of predictions that primary Defect energy levels reside outside the bandgap. We present experimental evidence that this enabling material property is present in the halide-lead perovskite, CH3NH3PbI3 (MAPbI3), consistent with theoretical predictions. By performing X-ray photoemission spectroscopy, we induce and track dynamic chemical and electronic transformations in the perovskite. These data show compositional changes that begin immediately with exposure to X-ray irradiation, whereas the predominant electronic structure of the thin film on compact TiO2 appears tolerant to the formation of compensating Defect pairs of VI and VMA and for a large range of I/Pb ratios. Changing film composition is correlated with a shift of the valence-band maximum only as the halide–lead ratio drops below 2.5. This delay is attributed to the invariance of MAPbI3 electronic structure to distributed def...
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identifying Defect tolerant semiconductors with high minority carrier lifetimes beyond hybrid lead halide perovskites
MRS Communications, 2015Co-Authors: Riley E Brandt, Vladan Stevanovic, David S Ginley, Tonio BuonassisiAbstract:The emergence of methyl-ammonium lead halide (MAPb X 3 ) perovskites motivates the identification of unique properties giving rise to exceptional bulk transport properties, and identifying future materials with similar properties. Here, we propose that this “Defect Tolerance” emerges from fundamental electronic-structure properties, including the orbital character of the conduction and valence band extrema, the charge-carrier effective masses, and the static dielectric constant. We use MaterialsProject.org searches and detailed electronic-structure calculations to demonstrate these properties in other materials than MAPb X 3 . This framework of materials discovery may be applied more broadly, to accelerate discovery of new semiconductors based on emerging understanding of recent successes.
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identifying Defect tolerant semiconductors with high minority carrier lifetimes beyond hybrid lead halide perovskites
arXiv: Materials Science, 2015Co-Authors: Riley E Brandt, Vladan Stevanovic, David S Ginley, Tonio BuonassisiAbstract:The emergence of methyl-ammonium lead halide (MAPbX3) perovskites motivates the identification of unique properties giving rise to exceptional bulk transport properties, and identifying future materials with similar properties. Here, we propose that this "Defect Tolerance" emerges from fundamental electronic structure properties, including the orbital character of the conduction and valence band extrema, the effective masses, and the static dielectric constant. We use MaterialsProject.org searches and detailed electronic-structure calculations to demonstrate these properties in other materials than MAPbX3. This framework of materials discovery may be applied more broadly, to accelerate discovery of new semiconductors based on emerging understanding of recent successes.
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Defect tolerant semiconductors for solar energy conversion
Journal of Physical Chemistry Letters, 2014Co-Authors: Andriy Zakutayev, Vladan Stevanovic, David S Ginley, Christopher M Caskey, Angela N Fioretti, Julien Vidal, Eric TeaAbstract:Defect Tolerance is the tendency of a semiconductor to keep its properties despite the presence of crystallographic Defects. Scientific understanding of the origin of Defect Tolerance is currently missing. Here we show that semiconductors with antibonding states at the top of the valence band are likely to be tolerant to Defects. Theoretical calculations demonstrate that Cu3N with antibonding valence band maximum has shallow intrinsic Defects and no surface states, in contrast to GaN with bonding valence band maximum. Experimental measurements indicate shallow native donors and acceptors in Cu3N thin films, leading to 1016–1017 cm–3 doping with either electrons or holes depending on the growth conditions. The experimentally measured bipolar doping and the solar-matched optical absorption onset (1.4 eV) make Cu3N a promising candidate absorber for photovoltaic and photoelectrochemical solar cells, despite the calculated indirect fundamental band gap (1.0 eV). These conclusions can be extended to other mate...
Maksym V Kovalenko - One of the best experts on this subject based on the ideXlab platform.
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properties and potential optoelectronic applications of lead halide perovskite nanocrystals
Science, 2017Co-Authors: Maksym V Kovalenko, Loredana Protesescu, Maryna I BodnarchukAbstract:Semiconducting lead halide perovskites (LHPs) have not only become prominent thin-film absorber materials in photovoltaics but have also proven to be disruptive in the field of colloidal semiconductor nanocrystals (NCs). The most important feature of LHP NCs is their so-called Defect-Tolerance—the apparently benign nature of structural Defects, highly abundant in these compounds, with respect to optical and electronic properties. Here, we review the important differences that exist in the chemistry and physics of LHP NCs as compared with more conventional, tetrahedrally bonded, elemental, and binary semiconductor NCs (such as silicon, germanium, cadmium selenide, gallium arsenide, and indium phosphide). We survey the prospects of LHP NCs for optoelectronic applications such as in television displays, light-emitting devices, and solar cells, emphasizing the practical hurdles that remain to be overcome.
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lead halide perovskite nanocrystals in the research spotlight stability and Defect Tolerance
ACS energy letters, 2017Co-Authors: He Huang, Maksym V Kovalenko, Maryna I Bodnarchuk, Stephen V Kershaw, Andrey L RogachAbstract:This Perspective outlines basic structural and optical properties of lead halide perovskite colloidal nanocrystals, highlighting differences and similarities between them and conventional II–VI and III–V semiconductor quantum dots. A detailed insight into two important issues inherent to lead halide perovskite nanocrystals then follows, namely, the advantages of Defect Tolerance and the necessity to improve their stability in environmental conditions. The Defect Tolerance of lead halide perovskites offers an impetus to search for similar attributes in other related heavy metal-free compounds. We discuss the origins of the significantly blue-shifted emission from CsPbBr3 nanocrystals and the synthetic strategies toward fabrication of stable perovskite nanocrystal materials with emission in the red and infrared parts of the optical spectrum, which are related to fabrication of mixed cation compounds guided by Goldschmidt Tolerance factor considerations. We conclude with the view on perspectives of use of th...
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harnessing Defect Tolerance at the nanoscale highly luminescent lead halide perovskite nanocrystals in mesoporous silica matrixes
Nano Letters, 2016Co-Authors: Dmitry N Dirin, Loredana Protesescu, David Trummer, Ilia V Kochetygov, Sergii Yakunin, Frank Krumeich, Nicholas P Stadie, Maksym V KovalenkoAbstract:Colloidal lead halide perovskite nanocrystals (NCs) have recently emerged as a novel class of bright emitters with pure colors spanning the entire visible spectral range. Contrary to conventional quantum dots, such as CdSe and InP NCs, perovskite NCs feature unusual, Defect-tolerant photophysics. Specifically, surface dangling bonds and intrinsic point Defects such as vacancies do not form midgap states, known to trap carriers and thereby quench photoluminescence (PL). Accordingly, perovskite NCs need not be electronically surface-passivated (with, for instance, ligands and wider-gap materials) and do not noticeably suffer from photo-oxidation. Novel opportunities for their preparation therefore can be envisaged. Herein, we show that the infiltration of perovskite precursor solutions into the pores of mesoporous silica, followed by drying, leads to the template-assisted formation of perovskite NCs. The most striking outcome of this simple methodology is very bright PL with quantum efficiencies exceeding 5...
Yaqing Feng - One of the best experts on this subject based on the ideXlab platform.
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auto passivation of crystal Defects in hybrid imidazolium methylammonium lead iodide films by fumigation with methylamine affords high efficiency perovskite solar cells
Nano Energy, 2019Co-Authors: Yi Zhang, Giulia Grancini, Zhaofu Fei, Erfan Shirzadi, Xuehui Liu, Emad Oveisi, Farzaneh Fadaei Tirani, Rosario Scopelliti, Yaqing FengAbstract:Abstract Hybrid perovskite solar cells have attracted tremendous interest in the photovoltaic community. Despite their high Defect Tolerance, reducing the trap density by material engineering and surface modification is still critical to further boost performance. Here, methylammonium lead(II) iodide perovskite has been doped with imidazolium iodide in high concentrations (10–30 mol%) to boost solar cell performance, by passivating Defects. Fumigation with methylamine results in the deprotonation of the embedded imidazolium cations, generating imidazole and methylammonium cations. The resulting (neutral) imidazole is extruded from the 3-D perovskite crystal and distributes around the crystal leading to auto-passivation of crystal Defects. The structure of the imidazolium-PbI3 salt intermediate (i.e. formed in the absence of the methylammonium cation) has been determined and the resulting perovskite film characterized. Employed in solar cells, a power conversion efficiency (PCE) up to 20.14% is demonstrated.
Mingchu Tang - One of the best experts on this subject based on the ideXlab platform.
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origin of Defect Tolerance in inas gaas quantum dot lasers grown on silicon
Journal of Lightwave Technology, 2020Co-Authors: Zizhuo Liu, Mickael Martin, T Baron, Siming Chen, A J Seeds, R V Penty, I H White, Huiyun Liu, Constanze Hantschmann, Mingchu TangAbstract:High-performance III–V quantum-dot lasers monolithically grown on Si substrates have been demonstrated as a promising solution to realize Si-based laser sources with very low threshold current density, high output power, and long lifetime, even with relatively high density of Defects due to the material dissimilarities between III–Vs and Si. On the other hand, although conventional III–V quantum-well lasers grown on Si have been demonstrated after great efforts worldwide for more than 40 years, their practicality is still a great challenge because of their very high threshold current density and very short lifetime. However, the physical mechanisms behind the superior performance of silicon-based III–V quantum-dot lasers remain unclear. In this paper, we directly compare the performance of a quantum-well and a quantum-dot laser monolithically grown on on-axis Si (001) substrates, both experimentally and theoretically, under the impact of the same density of threading dislocations. A quantum-dot laser grown on a Si substrate with a high operating temperature (105 °C) has been demonstrated with a low threshold current density of 173 A/cm2 and a high single facet output power >100 mW at room temperature, while there is no lasing operation for the quantum-well device at room temperature even at high injection levels. By using a rate equation travelling-wave model, the quantum-dot laser's superior performance compared with its quantum well-based counterpart on Si is theoretically explained in terms of the unique properties of quantum dots, i.e., efficient carrier capture and high thermal energy barriers preventing the carriers from migrating into Defect states.
