Asynchronous Photoexcited Electronic and Structural Relaxation in Lead-Free Perovskites

Liu, Cunming; Wang, Yingqi; Geng, Huifang; Zhu, Taishan; Ertekin, Elif; Gosztola, David; Yang, Sizhuo; Huang, Jier; Yang, Bin; Han, Keli; Canton, Sophie E.; Kong, Qingyu; Zheng, Kaibo; Zhang, Xiaoyi

doi:10.1021/jacs.9b04557

Title: Asynchronous Photoexcited Electronic and Structural Relaxation in Lead-Free Perovskites

Journal Article · 30 July 2019 · Journal of the American Chemical Society

DOI: https://doi.org/10.1021/jacs.9b04557 · OSTI ID:1571478

Liu, Cunming ^[1]; Wang, Yingqi ^[2]; Geng, Huifang ^[3]; Zhu, Taishan ^[4];

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Argonne National Lab. (ANL), Argonne, IL (United States). X-ray Science and Division
Center for High Pressure Science and Technology Advanced Research, Shanghai (China)
Extreme Light Infrastructure Attosecond Light Pulse Source (ELI-ALPS), Szeged (Hungary). ELI-HU
Univ. of Illinois at Urbana-Champaign, Urbana, IL (United States). Dept. of Mechanical Science and Engineering
Argonne National Lab. (ANL), Argonne, IL (United States). Center for Nanoscale Materials
Marquette Univ., Milwaukee, WI (United States). Dept. of Chemistry
Chinese Academy of Science, Dalian (China). Dalian Inst. of Chemical Physics, State Key Lab. of Molecular Reaction Dynamics
Extreme Light Infrastructure Attosecond Light Pulse Source (ELI-ALPS), Szeged (Hungary). ELI-HU; Deutsches Elektonen Synchrotron (DESY). Hamburg (Germany). Attosecond Science Group
L’Orme des Merisiers St Aubin, Gif-sur-Yvette (France). Sychrotron Soleil
Lund Univ., Lund (Sweden). Dept. of Chemical Physics and Nanolund; Technical Univ. of Denmark, Kongens Lyngby (Denmark). Dept. of Chemistry

Vacancy-ordered lead free perovskites with more stable crystalline structure have been intensively explored as the alternatives for resolving the toxic and long-term stable issues of Lead halide perovskites (LHPs). The dispersive energy bands produced by the closely packed halide octahedral sublattice in these perovskites are meanwhile anticipated to facility the mobility of charge carriers. However, these perovskites suffer from unexpectedly poor charge carrier transport. To tackle this issue, we have employed the ultrafast, elemental-specific X-ray transient absorption (XTA) spectroscopy to directly probe the photoexcited electronic and structural dynamics of a prototypical vacancy-ordered lead-free perovskite (Cs₃Bi₂Br₉). We have discovered that the photogenerated holes quickly self-trapped at Br centers, simultaneously distorting the local lattice structure, likely forming small polarons in the configuration of V_k center (Br₂^- dimer). More significantly, we have found a surprisingly long-lived, structural distorted state with a lifetime of ~ 59 μs, which is about three orders of magnitude slower than that of the charge carrier recombination. Such long-lived structural distortion may produce a transient “background” under continuous light illumination, influencing the charge carrier transport along the lattice framework.

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Research Organization:: Argonne National Laboratory (ANL), Argonne, IL (United States)

Sponsoring Organization:: China Scholarship Council; National Natural Science Foundation of China (NSFC); National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities Division