The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
Run Long - One of the best experts on this subject based on the ideXlab platform.
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Doping-Induced Charge Localization Suppresses Electron-Hole Recombination in Copper Zinc Tin Sulfide: Quantum Dynamics Combined with Deep Neural Networks Analysis.
The journal of physical chemistry letters, 2021Co-Authors: Zhaosheng Zhang, Yan Zhang, Jiazheng Wang, Run LongAbstract:Nonradiative Electron-Hole Recombination constitutes a major route for charge and energy losses in copper zinc tin sulfide (CZTS) solar cells. Using a combination of nonadiabatic (NA) molecular dynamics and deep neural networks (DNN), we demonstrated that Electron-Hole Recombination is notably retarded by doping with Ag and Ag+Cd. The replacement of lighter Cu and/or Zn with heavier Ag and/or Cd reduces the NA coupling by separating electron and hole wave functions. Such replacement suppresses atomic motions and makes the phonon modes move to low-frequency region, which reduces NA coupling further but inhibits decoherence. The small magnitudes of NA coupling beat the long coherence time, delaying the Electron-Hole Recombination from the Ag+Cd-codoping to the Ag doping system compared with pristine CZTS. The NA couplings predicted by the DNN algorithm lead to the time scales in agreement with the direct simulations. The study provides a robust strategy to design high-performance CZTS solar cells.
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Charge localization control of electron–hole Recombination in multilayer two-dimensional Dion–Jacobson hybrid perovskites
Journal of Materials Chemistry A, 2020Co-Authors: Ran Shi, Zhaosheng Zhang, Wei-hai Fang, Run LongAbstract:Two-dimensional (2D) Dion–Jacobson (DJ) organic–inorganic hybrid halide perovskites hold great potential for optoelectronics and solar cells. Interestingly, experimental excited-state lifetime is longer in (3AMP)(MA)n−1PbnI3n+1 than (4AMP)(MA)n−1PbnI3n+1 (3AMP = 3-(aminomethyl)piperidinium, 4AMP = 4-(aminomethyl)piperidinium, MA = CH3NH3+) regardless of the value of n despite 3AMP having a smaller bandgap. Using ab initio nonadiabatic (NA) molecular dynamics combined with time-domain density functional theory, we focus on the n = 2 perovskite and demonstrate that stronger hydrogen bonding interaction and larger octahedral tilting cause significant delocalization of the hole wave function in (4AMP)(MA)Pb2I7 and accelerates the electron–hole Recombination by a factor of 5 compared to (3AMP)(MA)Pb2I7 due to an increased NA coupling. The inorganic component stretching mode and coupled inorganic and organic collective motions accelerate decoherence to sub-4 fs in the two materials. The simulations rationalize the experimentally observed puzzle of excited-state lifetime in the 2D DJ perovskite and suggest a rational way to optimize the performance of perovskite devices.
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Ferroelastic domains drive charge separation and suppress Electron-Hole Recombination in all-inorganic halide perovskites: time-domain ab initio analysis.
Nanoscale horizons, 2020Co-Authors: Ran Shi, Zhaosheng Zhang, Wei-hai Fang, Run LongAbstract:All-inorganic perovskites have great potential in photovoltaic applications and their performance is subject to phonon-assisted charge Recombination dynamics. Local microstructures, such as ferroelastic domains, are considered to have a significant influence on the charge carrier lifetime in the CsPbBr3 perovskite. Employing a combination of time-domain density functional theory and nonadiabatic (NA) molecular dynamics simulations, we demonstrate that the formation of ferroelastic domains weakens the NA coupling and suppresses the non-radiative Electron-Hole Recombination. This effect originates from the ferroelastic domains separating electron and hole wave functions spatially and decreasing the NA coupling by a factor of 2.4 compared to pristine CsPbBr3, delaying Electron-Hole Recombination by a factor of 4.2. We also show that symmetry breaking enhances electronic-vibrational interactions, activating more phonon modes and accelerating quantum decoherence by 1 fs or so, which further slows Recombination. Both factors compete successfully with the slightly reduced bandgap of about 0.2 eV and prolong the charge carrier lifetime to several nanoseconds. Our study advances the understanding of the atomistic mechanism for inhibited Recombination in the CsPbBr3 perovskite in the presence of ferroelastic domains, providing an effective route to design high-performance all-inorganic halide perovskites.
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Weak temperature-dependent hole injection and electron–hole Recombination at the CH3NH3PbI3/NiO heterojunction: a time-domain ab initio study
Journal of Materials Chemistry A, 2020Co-Authors: Wei-hai Fang, Run LongAbstract:Inorganic hole transport material (HTM) NiO is superior to traditional organic HTMs due to its high stability and conductivity. Efficient charge separation and slow charge Recombination are two key important steps in determining the efficiency of solar cells but they often show strong temperature dependence. Using nonadiabatic molecular dynamics combined with ab initio time-domain density functional theory, we have demonstrated that the time scales for both hole transfer and electron–hole Recombination show weak temperature dependence in MAPbI3/NiO perovskite solar cells. The hole transfer occurs on sub-100 fs at both high and low temperatures. Hole transfer proceeds slightly faster at high temperature than low temperature due to enhanced NA coupling. Notably, the hole remains hot over 200 fs energy relaxation before cooling to interact with the remaining electrons, form excitons and accelerate electron–hole Recombination, providing an excellent advantage for solar energy applications. Following charge separation, the electron–hole Recombination takes place in several nanoseconds at both low and high temperatures. The acceleration only by a factor of below 2 arises because increased atomic motions cause rapid loss of coherence, which competes successfully with the enhanced NA coupling. The detailed atomistic understanding of the reported results allows us to generalize the conclusions to other hole transport materials and suggests weak temperature-dependent charge dynamics properties enabling the high performance of perovskite solar cells.
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Anomalous Temperature-Dependent Charge Recombination in CH3NH3PbI3 Perovskite: Key Roles of Charge Localization and Thermal Effect.
ACS applied materials & interfaces, 2019Co-Authors: Yutong Wang, Run LongAbstract:Optimizing metal halide perovskite solar cells necessitates understanding of nonradiative Electron-Hole Recombination because it comprises a dominant route for charge and energy losses. In principle, the Electron-Hole Recombination rate increases as temperature grows due to enhanced electron-phonon coupling. Experiments defy this expectation in MAPbI3 (MA = CH3NH3+). By performing nonadiabatic (NA) molecular dynamics analyses combined with time-domain density functional theory simulations, we demonstrate that nonradiative Electron-Hole Recombination in MAPbI3 at high temperature occurs more slowly than that at low temperature. First and most important, increasing temperature enhances thermal disorder and leads to significant distortion of the inorganic Pb-I framework, giving rise to electron and hole wave functions locating spatial separation and reducing NA coupling by a factor of 28% in comparison with low temperature. Second, rising temperature enhances the thermal fluctuations of both the inorganic and organic components that accelerate decoherence process by a factor of 12%. Both factors, particularly the small NA coupling, contribute to suppressing Electron-Hole Recombination at high temperature. The simulations show excellent agreement with experiments and emphasize how the charge localization driven by thermal effects impacts Electron-Hole Recombination in perovskites and advances our understanding of the unusual charge dynamics.
Oleg V. Prezhdo - One of the best experts on this subject based on the ideXlab platform.
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Low-frequency lattice phonons in halide perovskites explain high defect tolerance toward Electron-Hole Recombination.
Science advances, 2020Co-Authors: Weibin Chu, Oleg V. Prezhdo, Qijing Zheng, Jin Zhao, Wissam A. SaidiAbstract:Low-cost solution-based synthesis of metal halide perovskites (MHPs) invariably introduces defects in the system, which could form Shockley-Read-Hall (SRH) Electron-Hole Recombination centers detrimental to solar conversion efficiency. Here, we investigate the nonradiative Recombination processes due to native point defects in methylammonium lead halide (MAPbI3) perovskites using ab initio nonadiabatic molecular dynamics within surface-hopping framework. Regardless of whether the defects introduce a shallow or deep band state, we find that charge Recombination in MAPbI3 is not enhanced, contrary to predictions from SRH theory. We demonstrate that this strong tolerance against defects, and hence the breakdown of SRH, arises because the photogenerated carriers are only coupled with low-frequency phonons and electron and hole states overlap weakly. Both factors appreciably decrease the nonadiabatic coupling. We argue that the soft nature of the inorganic lattice with small bulk modulus is key for defect tolerance, and hence, the findings are general to other MHPs.
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Halide Composition Controls Electron–Hole Recombination in Cesium–Lead Halide Perovskite Quantum Dots: A Time Domain Ab Initio Study
The journal of physical chemistry letters, 2018Co-Authors: Andrey S. Vasenko, Run Long, Oleg V. PrezhdoAbstract:We demonstrate that halide content strongly affects nonradiative electron–hole Recombination in all-inorganic perovskite quantum dots (QDs). Using time domain density functional theory and nonadiabatic molecular dynamics, we show that replacing half of the bromines with iodines in a CsPbBr3 QD extends the charge carrier lifetime by a factor of 5, while complete replacement extends the lifetime by a factor of 8. Doping with iodines decreases the nonadiabatic charge–phonon coupling because iodines are heavier and slower than bromines and because the overlap between the electron and hole wave functions is reduced. In general, the nonradiative electron–hole Recombination proceeds slowly, on a nanosecond time scale, due to small sub-1 meV nonadiabatic coupling and short sub-10 fs coherence times. The obtained Recombination times and their dependence on the halogen content show excellent agreement with experiments. Our study suggests that the power conversion efficiencies of solar cells can be controlled by cha...
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Lewis Base Passivation of Hybrid Halide Perovskites Slows Electron–Hole Recombination: Time-Domain Ab Initio Analysis
The journal of physical chemistry letters, 2018Co-Authors: Lihong Liu, Run Long, Wei-hai Fang, Oleg V. PrezhdoAbstract:Nonradiative electron–hole Recombination plays a key role in determining photon conversion efficiencies in solar cells. Experiments demonstrate significant reduction in the Recombination rate upon passivation of methylammonium lead iodide perovskite with Lewis base molecules. Using nonadiabatic molecular dynamics combined with time-domain density functional theory, we find that the nonradiative charge Recombination is decelerated by an order of magnitude upon adsorption of the molecules. Thiophene acts by the traditional passivation mechanism, forcing electron density away from the surface. In contrast, pyridine localizes the electron at the surface while leaving it energetically near the conduction band edge. This is because pyridine creates a stronger coordinative bond with a lead atom of the perovskite and has a lower energy unoccupied orbital compared with thiophene due to the more electronegative nitrogen atom relative to thiophene’s sulfur. Both molecules reduce two-fold the nonadiabatic coupling an...
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Ferroelectric Alignment of Organic Cations Inhibits Nonradiative Electron–Hole Recombination in Hybrid Perovskites: Ab Initio Nonadiabatic Molecular Dynamics
The journal of physical chemistry letters, 2017Co-Authors: Joanna Jankowska, Oleg V. PrezhdoAbstract:Hybrid organic–inorganic perovskites show impressive potential for photovoltaic applications and currently give rise to one of the most vibrant research areas in the field. Until recently, the electrostatic interactions between their organic and inorganic components were considered mostly for stabilization of the fragile perovskite structure. We study the effect of local interactions of polar C–N bonds in the organic layer on the nonradiative electron–hole Recombination in the recently reported room-temperature ferroelectric hybrid perovskite, (benzylammonium)2PbCl4. Using nonadiabatic molecular dynamics and real-time time-dependent density functional theory, we show that ferroelectric alignment of the polar groups weakens the electron–phonon nonadiabatic coupling and inhibits the nonradiative charge Recombination. The effect is attributed to suppression of contributions of higher frequency phonons to the electron–phonon coupling. The coupling is dominated in the ferroelectric phase by slower collective m...
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Moderate Humidity Delays Electron-Hole Recombination in Hybrid Organic-Inorganic Perovskites: Time-Domain Ab Initio Simulations Rationalize Experiments.
The journal of physical chemistry letters, 2016Co-Authors: Run Long, Wei-hai Fang, Oleg V. PrezhdoAbstract:Experiments show both positive and negative changes in performance of hybrid organic–inorganic perovskite solar cells upon exposure to moisture. Ab initio nonadiabatic molecular dynamics reveals the influence of humidity on nonradiative electron–hole Recombination. In small amounts, water molecules perturb perovskite surface and localize photoexcited electron close to the surface. Importantly, deep electron traps are avoided. The electron–hole overlap decreases, and the excited state lifetime increases. In large amounts, water forms stable hydrogen-bonded networks, has a higher barrier to enter perovskite, and produces little impact on charge localization. At the same time, by contributing high frequency polar vibrations, water molecules increase nonadiabatic coupling and accelerate Recombination. In general, short coherence between electron and hole benefits photovoltaic response of the perovskites. The calculated Recombination time scales show excellent agreement with experiment. The time-domain atomist...
Wei-hai Fang - One of the best experts on this subject based on the ideXlab platform.
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Charge localization control of electron–hole Recombination in multilayer two-dimensional Dion–Jacobson hybrid perovskites
Journal of Materials Chemistry A, 2020Co-Authors: Ran Shi, Zhaosheng Zhang, Wei-hai Fang, Run LongAbstract:Two-dimensional (2D) Dion–Jacobson (DJ) organic–inorganic hybrid halide perovskites hold great potential for optoelectronics and solar cells. Interestingly, experimental excited-state lifetime is longer in (3AMP)(MA)n−1PbnI3n+1 than (4AMP)(MA)n−1PbnI3n+1 (3AMP = 3-(aminomethyl)piperidinium, 4AMP = 4-(aminomethyl)piperidinium, MA = CH3NH3+) regardless of the value of n despite 3AMP having a smaller bandgap. Using ab initio nonadiabatic (NA) molecular dynamics combined with time-domain density functional theory, we focus on the n = 2 perovskite and demonstrate that stronger hydrogen bonding interaction and larger octahedral tilting cause significant delocalization of the hole wave function in (4AMP)(MA)Pb2I7 and accelerates the electron–hole Recombination by a factor of 5 compared to (3AMP)(MA)Pb2I7 due to an increased NA coupling. The inorganic component stretching mode and coupled inorganic and organic collective motions accelerate decoherence to sub-4 fs in the two materials. The simulations rationalize the experimentally observed puzzle of excited-state lifetime in the 2D DJ perovskite and suggest a rational way to optimize the performance of perovskite devices.
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Ferroelastic domains drive charge separation and suppress Electron-Hole Recombination in all-inorganic halide perovskites: time-domain ab initio analysis.
Nanoscale horizons, 2020Co-Authors: Ran Shi, Zhaosheng Zhang, Wei-hai Fang, Run LongAbstract:All-inorganic perovskites have great potential in photovoltaic applications and their performance is subject to phonon-assisted charge Recombination dynamics. Local microstructures, such as ferroelastic domains, are considered to have a significant influence on the charge carrier lifetime in the CsPbBr3 perovskite. Employing a combination of time-domain density functional theory and nonadiabatic (NA) molecular dynamics simulations, we demonstrate that the formation of ferroelastic domains weakens the NA coupling and suppresses the non-radiative Electron-Hole Recombination. This effect originates from the ferroelastic domains separating electron and hole wave functions spatially and decreasing the NA coupling by a factor of 2.4 compared to pristine CsPbBr3, delaying Electron-Hole Recombination by a factor of 4.2. We also show that symmetry breaking enhances electronic-vibrational interactions, activating more phonon modes and accelerating quantum decoherence by 1 fs or so, which further slows Recombination. Both factors compete successfully with the slightly reduced bandgap of about 0.2 eV and prolong the charge carrier lifetime to several nanoseconds. Our study advances the understanding of the atomistic mechanism for inhibited Recombination in the CsPbBr3 perovskite in the presence of ferroelastic domains, providing an effective route to design high-performance all-inorganic halide perovskites.
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Weak temperature-dependent hole injection and electron–hole Recombination at the CH3NH3PbI3/NiO heterojunction: a time-domain ab initio study
Journal of Materials Chemistry A, 2020Co-Authors: Wei-hai Fang, Run LongAbstract:Inorganic hole transport material (HTM) NiO is superior to traditional organic HTMs due to its high stability and conductivity. Efficient charge separation and slow charge Recombination are two key important steps in determining the efficiency of solar cells but they often show strong temperature dependence. Using nonadiabatic molecular dynamics combined with ab initio time-domain density functional theory, we have demonstrated that the time scales for both hole transfer and electron–hole Recombination show weak temperature dependence in MAPbI3/NiO perovskite solar cells. The hole transfer occurs on sub-100 fs at both high and low temperatures. Hole transfer proceeds slightly faster at high temperature than low temperature due to enhanced NA coupling. Notably, the hole remains hot over 200 fs energy relaxation before cooling to interact with the remaining electrons, form excitons and accelerate electron–hole Recombination, providing an excellent advantage for solar energy applications. Following charge separation, the electron–hole Recombination takes place in several nanoseconds at both low and high temperatures. The acceleration only by a factor of below 2 arises because increased atomic motions cause rapid loss of coherence, which competes successfully with the enhanced NA coupling. The detailed atomistic understanding of the reported results allows us to generalize the conclusions to other hole transport materials and suggests weak temperature-dependent charge dynamics properties enabling the high performance of perovskite solar cells.
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Dopant Control of Electron-Hole Recombination in Cesium-Titanium Halide Double Perovskite by Time Domain Ab Initio Simulation: Codoping Supersedes Monodoping.
The journal of physical chemistry letters, 2018Co-Authors: Lu Qiao, Wei-hai Fang, Run LongAbstract:Using nonadiabatic (NA) molecular dynamics combined with time domain density functional theory, we simulate Electron-Hole Recombination in pristine and doped inorganic Pb-free double perovskite Cs2TiBr6. We show that replacing the titanium and/or bromine with silicon and/or chlorine extends the charge carrier lifetime. Importantly, dopants avoid deep traps despite the fact that they do not change the fundamental band gap of Cs2TiBr6, and they decrease the NA electron-phonon coupling and accelerate decoherence arising from the reduced overlap of electron and hole wave functions as well as fast phonon modes induced by light dopants, respectively, suppressing Electron-Hole Recombination. More importantly, codoping can reduce the formation energy of silicon and achieve higher doping concentration, potentially increasing the lifetime further. Our study suggests a rational strategy to reduce energy losses by codoping in design of high-performance all-inorganic Pb-free perovskite solar cells.
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Unravelling the Effects of A-Site Cations on Nonradiative Electron-Hole Recombination in Lead Bromide Perovskites: Time-Domain ab Initio Analysis.
Journal of Physical Chemistry Letters, 2018Co-Authors: Jinlu He, Wei-hai Fang, Run LongAbstract:Lead bromide perovskites APbBr3 (A = Cs, MA, FA) hold great promise in optoelectronics and photovoltaics. Because the band gaps of the three materials are similar, and also because the A-site cation does not contribute to band edges, one would expect a minor influence of A-site cation on the excited-state lifetime of the perovskites. Experiments defy that expectation. By performing ab initio nonadiabatic (NA) molecular dynamics combined with time-domain density functional simulations, we demonstrate that the nonradiative electron–hole Recombination times are in the order FAPbBr3 > MAPbBr3 > CsPbBr3, which are determined by the NA electron–phonon coupling because decoherence times are similar. The simulations show that the larger A-site cation and the smaller NA coupling because larger A-site cation suppresses the Pb–Br cages’ motion. The electron–hole Recombination is slow, ranging from subnanosecond to nanoseconds, because the NA coupling is small, less than 3 meV, and because decoherence time is slow, l...
N. Holonyak - One of the best experts on this subject based on the ideXlab platform.
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microwave determination of electron hole Recombination dynamics from spontaneous to stimulated emission in a quantum well microcavity laser
Applied Physics Letters, 2010Co-Authors: Chaohsin Wu, Han Wui Then, Milton Feng, N. HolonyakAbstract:By studying the optical microwave frequency response of a microcavity quantum-well vertical cavity surface-emitting laser (VCSEL) in the transition, over a low (a spread-out) mode density, from spontaneous to coherent operation, we resolve the dynamics (spontaneous to stimulated) of Electron-Hole Recombination and reveal the existence of “fast” spontaneous Recombination (τBspon<159 ps) in a carrier population generally characterized by a large average lifetime of ∼1 ns (Δn/τav=Δn1/τfast+(Δn−Δn1)/τslow,τfast<τslow). The measured average spontaneous lifetime is not a constant but is altered by the device size, geometry, and boundary conditions (e. g., cavity and current input-output boundary conditions).
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Microwave determination of Electron-Hole Recombination dynamics from spontaneous to stimulated emission in a quantum-well microcavity laser
Applied Physics Letters, 2010Co-Authors: Han Wui Then, Milton Feng, N. HolonyakAbstract:By studying the optical microwave frequency response of a microcavity quantum-well vertical cavity surface-emitting laser (VCSEL) in the transition, over a low (a spread-out) mode density, from spontaneous to coherent operation, we resolve the dynamics (spontaneous to stimulated) of Electron-Hole Recombination and reveal the existence of “fast” spontaneous Recombination (τBspon
Jinlu He - One of the best experts on this subject based on the ideXlab platform.
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Unravelling the Effects of A-Site Cations on Nonradiative Electron-Hole Recombination in Lead Bromide Perovskites: Time-Domain ab Initio Analysis.
Journal of Physical Chemistry Letters, 2018Co-Authors: Jinlu He, Wei-hai Fang, Run LongAbstract:Lead bromide perovskites APbBr3 (A = Cs, MA, FA) hold great promise in optoelectronics and photovoltaics. Because the band gaps of the three materials are similar, and also because the A-site cation does not contribute to band edges, one would expect a minor influence of A-site cation on the excited-state lifetime of the perovskites. Experiments defy that expectation. By performing ab initio nonadiabatic (NA) molecular dynamics combined with time-domain density functional simulations, we demonstrate that the nonradiative electron–hole Recombination times are in the order FAPbBr3 > MAPbBr3 > CsPbBr3, which are determined by the NA electron–phonon coupling because decoherence times are similar. The simulations show that the larger A-site cation and the smaller NA coupling because larger A-site cation suppresses the Pb–Br cages’ motion. The electron–hole Recombination is slow, ranging from subnanosecond to nanoseconds, because the NA coupling is small, less than 3 meV, and because decoherence time is slow, l...
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Unravelling the Effects of A-Site Cations on Nonradiative Electron-Hole Recombination in Lead Bromide Perovskites: Time-Domain ab Initio Analysis.
Journal of Physical Chemistry Letters, 2018Co-Authors: Jinlu He, Wei-hai Fang, Run LongAbstract:Lead bromide perovskites APbBr3 (A = Cs, MA, FA) hold great promise in optoelectronics and photovoltaics. Because the band gaps of the three materials are similar, and also because the A-site cation does not contribute to band edges, one would expect a minor influence of A-site cation on the excited-state lifetime of the perovskites. Experiments defy that expectation. By performing ab initio nonadiabatic (NA) molecular dynamics combined with time-domain density functional simulations, we demonstrate that the nonradiative electron–hole Recombination times are in the order FAPbBr3 > MAPbBr3 > CsPbBr3, which are determined by the NA electron–phonon coupling because decoherence times are similar. The simulations show that the larger A-site cation and the smaller NA coupling because larger A-site cation suppresses the Pb–Br cages’ motion. The electron–hole Recombination is slow, ranging from subnanosecond to nanoseconds, because the NA coupling is small, less than 3 meV, and because decoherence time is slow, l...