Asynchronous Photoexcited Electronic and Structural Relaxation in Lead-Free Perovskites

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

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review


Vacancy-ordered lead-free perovskites with more-stable crystalline structures have been intensively explored as the alternatives for resolving the toxic and long-term stability 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 Vk center (Br2 - dimer). More significantly, we have found a surprisingly long-lived, structural distorted state with a lifetime of ∼59 μs, which is ∼3 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. 

Original languageEnglish
JournalJournal of the American Chemical Society
Issue number33
Pages (from-to)13074-13080
Number of pages7
Publication statusPublished - 2019

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