Thermal Expansion Behavior of Halide Perovskite Single Crystals Across a Broad Temperature Range

Halide perovskite crystals are garnering significant interest as a promising material for next‐generation solar cells. They are also anticipated to be applicable in devices used across a wide temperature range, including X‐ray and γ‐ray detectors, as well as in solar cells designed for satellite environments. The coefficient of thermal expansion of halide perovskite crystals is a critical physical property to understand, especially given the potential for mechanical degradation in layered devices due to abrupt temperature fluctuations, which may result in mismatched expansion coefficients among different layers. In this study, we employed single crystal X‐ray diffraction techniques to investigate the coefficient of thermal expansion of halide perovskite crystals, with a specific focus on CH3NH3PbI3, across an extensive temperature range. Our findings reveal that the lattice parameters exhibit discontinuous changes during the phase transition from the β‐phase to the γ‐phase, in stark contrast to the α to β phase transition. This observation implies that structural phase transitions at low temperatures could significantly affect the longevity and reliability of devices incorporating these materials. The methodology we have utilized for assessing coefficient of thermal expansion via single crystal structural analysis at low temperatures presents a substantial advancement in the research of halide perovskite crystals.