Chalcogenide perovskites(CPs) exhibiting lower band gaps than oxide perovskites and higher stability than halide perovskites are promising materials for photovoltaic and optoelectronic applications. For such applicati...Chalcogenide perovskites(CPs) exhibiting lower band gaps than oxide perovskites and higher stability than halide perovskites are promising materials for photovoltaic and optoelectronic applications. For such applications, the absence of deep defect levels serving as recombination centers(dubbed defect tolerance) is a highly desirable property. Here,using density functional theory(DFT) calculations, we study the intrinsic defects in BaZrS_(3), a representative CP material.We compare Hubbard-U and hybrid functional methods, both of which have been widely used in addressing the band gap problem of semi-local functionals in DFT. We find that tuning the U value to obtain experimental bulk band gap and then using the obtained U value for defect calculations may result in over-localization of defect states. In the hybrid functional calculation, the band gap of BaZrS_(3)can be accurately obtained. We observe the formation of small S-atom clusters in both methods, which tend to self-passivate the defects from forming mid-gap levels. Even though in the hybrid functional calculations several relatively deep defects are observed, all of them exhibit too high formation energy to play a significant role if the materials are prepared under thermal equilibrium.BaZrS_(3)is thus expected to exhibit sufficient defect tolerance promising for photovoltaic and optoelectronic applications.展开更多
Oxygen-containing rare-earth metal hydride YH_xO_y,is a newly found photochromic material showing fast photoresponse.While its preparation method,optical properties and structural features have been studied extensivel...Oxygen-containing rare-earth metal hydride YH_xO_y,is a newly found photochromic material showing fast photoresponse.While its preparation method,optical properties and structural features have been studied extensively,the photochromic mechanism in YH_xO_yremains unknown Here,using excited-state molecular dynamics simulation based on the recently developed real-time time-dependent density functional theory(RT-TDDFT)method,we study the photochemical reactions in YH_xO_y.We find that under photoexcitation,dihydrogen defects are formed within 100 fs.The dihydrogen defect behaves as a shallow donor and renders the material strongly n-type doped,which could be responsible for the photochromic effect observed in YH_xO_y.We also find that oxygen concentration affects the metastability of the dihydrogen species,meaning that the energy barrier for the dihydrogen to dissociate is related to the oxygen concentration The highest barrier of 0.28 eV is found in our model with O/Y=1:8.If the oxygen concentration is too low,the dihydrogen will quickly dissociate when the excitation is turned off.If the oxygen concentration is too high,the dihydrogen dissociates even when the excitation is still on.展开更多
基金supported by the National Natural Science Foundation of China (11774365)the Natural Science Foundation of Shanghai (19ZR1421800)+4 种基金Shanghai International Cooperation Project (20520760900)the Opening Project and Science Foundation for Youth Scholar of State Key Laboratory of High Performance Ceramics and Superfine Microstructures (SKL201804 and SKL201803SIC) support by US National Science Foundation (NSF) (CBET1510121)US Department of Energy (DOE) (DEEE0007364)support by US NSF (CBET-1510948).support by US NSF (DMR-1506669)support by the Fundamental Research Funds for the Central Universities (DUT21RC(3) 033)。
文摘Chalcogenide perovskites(CPs) exhibiting lower band gaps than oxide perovskites and higher stability than halide perovskites are promising materials for photovoltaic and optoelectronic applications. For such applications, the absence of deep defect levels serving as recombination centers(dubbed defect tolerance) is a highly desirable property. Here,using density functional theory(DFT) calculations, we study the intrinsic defects in BaZrS_(3), a representative CP material.We compare Hubbard-U and hybrid functional methods, both of which have been widely used in addressing the band gap problem of semi-local functionals in DFT. We find that tuning the U value to obtain experimental bulk band gap and then using the obtained U value for defect calculations may result in over-localization of defect states. In the hybrid functional calculation, the band gap of BaZrS_(3)can be accurately obtained. We observe the formation of small S-atom clusters in both methods, which tend to self-passivate the defects from forming mid-gap levels. Even though in the hybrid functional calculations several relatively deep defects are observed, all of them exhibit too high formation energy to play a significant role if the materials are prepared under thermal equilibrium.BaZrS_(3)is thus expected to exhibit sufficient defect tolerance promising for photovoltaic and optoelectronic applications.
基金the support by the National Natural Science Foundation of China(11774365)。
文摘Oxygen-containing rare-earth metal hydride YH_xO_y,is a newly found photochromic material showing fast photoresponse.While its preparation method,optical properties and structural features have been studied extensively,the photochromic mechanism in YH_xO_yremains unknown Here,using excited-state molecular dynamics simulation based on the recently developed real-time time-dependent density functional theory(RT-TDDFT)method,we study the photochemical reactions in YH_xO_y.We find that under photoexcitation,dihydrogen defects are formed within 100 fs.The dihydrogen defect behaves as a shallow donor and renders the material strongly n-type doped,which could be responsible for the photochromic effect observed in YH_xO_y.We also find that oxygen concentration affects the metastability of the dihydrogen species,meaning that the energy barrier for the dihydrogen to dissociate is related to the oxygen concentration The highest barrier of 0.28 eV is found in our model with O/Y=1:8.If the oxygen concentration is too low,the dihydrogen will quickly dissociate when the excitation is turned off.If the oxygen concentration is too high,the dihydrogen dissociates even when the excitation is still on.
