Photoinduced metastable cation disorder in metal halide double perovskites
- Shunran Li
- Burak Guzelturk
- Conrad A. Kocoj
- Donald A. Walko
- Du Chen
- Haidan Wen
- Xian Xu
- Xiaoming Wang
- Bongjun Choi
- Zhibo Kang
- Borui Li
- Cunming Liu
- Suchismita Sarker
- Benjamin T. Diroll
- Xiaoyi Zhang
- Yong Q. Cai
- Yu He
- Deep Jariwala
- Yanfa Yan
- Diana Y. Qiu
- Peijun Guo
2026-07-24
Lead-free perovskites have emerged as environmentally benign alternatives to lead halide counterparts for photovoltaic and optoelectronic applications. Among them, the double perovskite Cs 2 AgInCl 6 family, with proper composition engineering, exhibits remarkable white-light emission characteristics enabled by strong electron-phonon coupling and the formation of self-trapped excitons (STEs). Despite these advantages, the fundamental photophysics and structural dynamics governing their excited-state behavior remain poorly understood. Here, we report a long-lived metastable phase in the Cs 2 AgInCl 6 double perovskite family and unravel this process and the concomitant electronic and structural evolution using a suite of tools including transient optical spectroscopy, time-resolved x-ray diffraction (TR-XRD), time-resolved x-ray absorption spectroscopy (TR-XAS), and inelastic x-ray scattering (IXS). We show that the photoinduced, transient metastable phase is associated with B-site [silver (Ag)–indium (In)] disorder, which induces a markedly reduced optical bandgap. Supported by TR-XRD and first-principles calculations, the Ag-In disorder drives the formation of Ag-rich and In-rich domains with millisecond lifetimes, with lifetimes increasing at lower temperatures. TR-XAS further reveals that the photogenerated STEs oxidize Ag + to Ag 2+ , which facilitates this highly temporally asymmetric order-disorder transition. Our findings demonstrate a previously unidentified mechanism, mediated by hole-localized STE formation, that enables prolongation of transient light-induced states to the multimillisecond regime in halide double perovskites, opening possibilities to harvesting the functional properties of metastable phases of these material systems.