Since the seminal work by Kojima et al. in 2009, solar cells based on hybrid organic-inorganic perovskites have attracted considerable attention and experienced an exponential growth, with photovoltaic efficiencies as...Since the seminal work by Kojima et al. in 2009, solar cells based on hybrid organic-inorganic perovskites have attracted considerable attention and experienced an exponential growth, with photovoltaic efficiencies as of today reaching above 22%. Despite such an impressive development, some key scientific issues of these materials, including the presence of toxic lead, the poor long-term device stability under heat and humidity conditions, and the anomalous hysteresis of the current-voltage curves shown by various solar cell devices, still remain unsolved and constitute an important focus of experimental and theoretical researchers throughout the world. Density functional theory calculations have been successfully applied to exploring structural and electronic properties of semiconductors, complementing the experimental results in search and discovery of novel functional materials. In this review, we summarize the current progress in perovskite photovoltaic materials from a theoretical perspective. We discuss design of lead-free perovskite materials, humidity-induced degradation mechanisms and possible origins for the observed solar cell hysteresis, and assess future research directions for advanced perovskite solar cells based on computational materials design and theoretical understanding of intrinsic properties.展开更多
Hybrid organic-inorganic perovskites are currently considered the most promising next-generation photovoltaic material.However,poor stability,arising from structural degradation under exposure to moisture,heat,and str...Hybrid organic-inorganic perovskites are currently considered the most promising next-generation photovoltaic material.However,poor stability,arising from structural degradation under exposure to moisture,heat,and strong current,remains a critical challenge for their device applications.Using ab initio nonadiabatic molecular dynamics,we demonstrate that methylamine fragments deriving from the dissociation of the methylammonium cation can undermine structural stability,produce deep hole traps,and decrease charge carrier lifetimes by 1-3 orders of magnitude.Both stability and charge lifetime can be restored by methylamine passivation with chlorines,which withdraw electrons from the lone electron pair of methylamine and bring the trap levels down into the valence band.The charge lifetime of the passivated system is even longer than that of the pristine perovskite.The simulations reveal the detailed microscopic mechanism underlying deterioration of perovskite performance due to molecular defects,and demonstrate an effective defect passivation strategy to obtain highly efficient and stable perovskite solar cells.展开更多
MAPbBr_(3)(MA=CH_(3)NH_(3)^(+))doping with bismuth increases electric conductivity,charge carrier density and photostability,reduces toxicity,and expands light absorption.However,Bi doping shortens excited-state lifet...MAPbBr_(3)(MA=CH_(3)NH_(3)^(+))doping with bismuth increases electric conductivity,charge carrier density and photostability,reduces toxicity,and expands light absorption.However,Bi doping shortens excited-state lifetimes due to formation of DY−charge recombination centers.Using nonadiabatic molecular dynamics and time-domain density functional theory,we demonstrate that the DY−center forms a deep,highly localized hole trap,which accelerates nonradiative relaxation ten-fold and is responsible for 90%of carrier losses.Hole trapping occurs by coupling between the valence band and the trap state,facilitated by the Br atoms surrounding the Bi dopant.Passivation of the DY−center with chlorines heals the local geometry distortion,eliminates the trap state,and makes the carrier lifetimes longer than even in pristine MAPbBr_(3).The decreased charge recombination arises from reduced nonadiabatic coupling and shortened coherence time,due to diminished electron–hole overlap around the passivated defect.Our study demonstrates accelerated nonradiative recombination in Bi-doped MAPbBr_(3),suggests a strategy for defect passivation and reduction of nonradiative energy losses,and provides atomistic insights into unusual defect properties of metal halide perovskites needed for rational design of high-performance perovskite solar cells and optoelectronic devices.展开更多
基金support of the National Natural Science Foundation of China,grant nos.21473183 and 21303079the Foundation for Polish Science,grant no.42.2016,for support through the START 2016 program+1 种基金US National Science Foundation,grant no.CHE-1565704US Department of Energy,grant no.DE-SC0014429,for financial support
文摘Since the seminal work by Kojima et al. in 2009, solar cells based on hybrid organic-inorganic perovskites have attracted considerable attention and experienced an exponential growth, with photovoltaic efficiencies as of today reaching above 22%. Despite such an impressive development, some key scientific issues of these materials, including the presence of toxic lead, the poor long-term device stability under heat and humidity conditions, and the anomalous hysteresis of the current-voltage curves shown by various solar cell devices, still remain unsolved and constitute an important focus of experimental and theoretical researchers throughout the world. Density functional theory calculations have been successfully applied to exploring structural and electronic properties of semiconductors, complementing the experimental results in search and discovery of novel functional materials. In this review, we summarize the current progress in perovskite photovoltaic materials from a theoretical perspective. We discuss design of lead-free perovskite materials, humidity-induced degradation mechanisms and possible origins for the observed solar cell hysteresis, and assess future research directions for advanced perovskite solar cells based on computational materials design and theoretical understanding of intrinsic properties.
基金This work was supported by the Beijing Natural Science Foundation(No.2212031)the National Natural Science Foundation of China(Nos.21973006,51861135101,and 21520102005)R.L.acknowledges the financial support by the Recruitment Program of Global Youth Experts of China and the Beijing Normal University Startup.O.V.P.acknowledges the support of the US Department of Energy(No.DE-SC0014429).
文摘Hybrid organic-inorganic perovskites are currently considered the most promising next-generation photovoltaic material.However,poor stability,arising from structural degradation under exposure to moisture,heat,and strong current,remains a critical challenge for their device applications.Using ab initio nonadiabatic molecular dynamics,we demonstrate that methylamine fragments deriving from the dissociation of the methylammonium cation can undermine structural stability,produce deep hole traps,and decrease charge carrier lifetimes by 1-3 orders of magnitude.Both stability and charge lifetime can be restored by methylamine passivation with chlorines,which withdraw electrons from the lone electron pair of methylamine and bring the trap levels down into the valence band.The charge lifetime of the passivated system is even longer than that of the pristine perovskite.The simulations reveal the detailed microscopic mechanism underlying deterioration of perovskite performance due to molecular defects,and demonstrate an effective defect passivation strategy to obtain highly efficient and stable perovskite solar cells.
基金the Beijing Science Foundation(No.2212031)the National Natural Science Foundation of China(Nos.51861135101,21973006,21573022,21688102 and 21590801)R.L.acknowledges the Recruitment Program of Global Youth Experts of China and the Beijing Normal University Startup.O.V.P.acknowledges funding from the U.S.Department of Energy(No.DE SC0014429).
文摘MAPbBr_(3)(MA=CH_(3)NH_(3)^(+))doping with bismuth increases electric conductivity,charge carrier density and photostability,reduces toxicity,and expands light absorption.However,Bi doping shortens excited-state lifetimes due to formation of DY−charge recombination centers.Using nonadiabatic molecular dynamics and time-domain density functional theory,we demonstrate that the DY−center forms a deep,highly localized hole trap,which accelerates nonradiative relaxation ten-fold and is responsible for 90%of carrier losses.Hole trapping occurs by coupling between the valence band and the trap state,facilitated by the Br atoms surrounding the Bi dopant.Passivation of the DY−center with chlorines heals the local geometry distortion,eliminates the trap state,and makes the carrier lifetimes longer than even in pristine MAPbBr_(3).The decreased charge recombination arises from reduced nonadiabatic coupling and shortened coherence time,due to diminished electron–hole overlap around the passivated defect.Our study demonstrates accelerated nonradiative recombination in Bi-doped MAPbBr_(3),suggests a strategy for defect passivation and reduction of nonradiative energy losses,and provides atomistic insights into unusual defect properties of metal halide perovskites needed for rational design of high-performance perovskite solar cells and optoelectronic devices.
