Centimeter-Scale In-Based Perovskite Single Crystals with Near 100% Quantum Yield via Self-Trapped Exciton Emission

Indium-based halide perovskites oftentimes exhibit limited photoluminescence quantum yield (PLQY) due to weak optical absorption, which restricts their utility in luminescent applications. However, self-trapped exciton (STE) modulation through crystal engineering offers a promising pathway to enhance emission efficiency. In this study, we report the low-temperature (20–85 °C) synthesis of centimeter-scale lead-free perovskite single crystals of CsIn 1– x Sb x Cl 4, which demonstrate intense broadband STE emission at room temperature and achieve an unprecedented PLQY of 100%, the highest reported value for indium-based halides to date. Femtosecond spectroscopy elucidated the physical origin by mapping the complete dynamics: the sub-picosecond (sub-ps) formation of the singlet 1 STE, its transition to the triplet 3 STE within tens to hundreds of ps, and the subsequent μs-scale radiative recombination. This work thus offers critical insights into STE-driven design strategies for next-generation optoelectronic devices of single component white-light emission.