Toward Long-Term Stability: Single-Crystal Alloys of Cesium-Containing Mixed Cation and Mixed Halide Perovskite

Perovskite
solar cells are strong competitors for silicon-based
ones, but suffer from poor long-term stability, for which the intrinsic
stability of perovskite materials is of primary concern. Herein, we
prepared a series of well-defined cesium-containing mixed cation and
mixed halide perovskite single-crystal alloys, which enabled systematic
investigations on their structural stabilities against light, heat,
water, and oxygen. Two potential phase separation processes are evidenced
for the alloys as the cesium content increases to 10% and/or bromide
to 15%. Eventually, a highly stable new composition, (FAPbI3)0.9(MAPbBr3)0.05­(CsPbBr3)0.05, emerges with a carrier lifetime of 16 μs.
It remains stable during at least 10 000 h water–oxygen
and 1000 h light stability tests, which is very promising for long-term
stable devices with high efficiency. The mechanism for the enhanced
stability is elucidated through detailed single-crystal structure
analysis. Our work provides a single-crystal-based paradigm for stability
investigation, leading to the discovery of stable new perovskite materials.