Vacuum-Temperature Synergistic Effects on Phase Stability and Carrier Mobility of Lead-triiodide Perovskites

Metal halide perovskites (MHPs) inherently feature soft ionic lattices, endowing their crystal structures with high sensitivity to both temperature and pressure. It has been well established that the lowering of temperature under atmospheric pressure induces phase shift in the typical CH₃NH₃PbI₃ (MAPbI₃) perovskites from tetragonal to orthorhombic structures, leading to a decreasing photovoltaic efficiency due to the poorer charge transport performance. Herein, we report an investigation into the synergistic effects of vacuum and temperatures on phase transition and charge transport dynamics of MHPs, which is designed to simulate the outer space environments with intrinsic temperature cycling and high vacuum. Surprisingly, we find that MAPbI₃ under high vacuum exhibits an unusual compression behavior during phase transitions and remains in the tetragonal phase even around 78 K. This phase stability is attributed to a substantial drop in thermal expansion coefficient under low pressure. The material achieves a superior carrier diffusion length (10.2-14.9 μm) in the simulated space environment, surpassing its performance in terrestrial settings. These results provide new insight into the structural stability of perovskites and highlight their applicability across various conditions.