Reversible, Photo‐Induced Lattice Distortions in Halide Perovskites

ABSTRACT The unique characteristics of soft‐lattice halide perovskites (HPs) have motivated extensive research into their application in semiconductor devices. Mechanically and chemically modulated strain in monocrystalline HPs improves stability and phase purity. However, a comprehensive understanding of the photoexcitation‐driven lattice distortions arising from the strong electron‐phonon coupling paired with the dynamics of the A‐site cation remains underdeveloped. Here, we present the transient lattice distortions occurring in single crystal MAPbBr 3 , FAPbBr 3 , and CsPbBr 3 in response to above‐bandgap light excitation. Using an X‐ray probe, we uncover reversible and hysteresis‐free photoinduced lattice distortion. We find that the photoinduced distortion in the HPs is a function of the pump power, with CsPbBr 3 showing the highest resilience against lattice deformation with a 0.062% change in its out‐of‐plane lattice parameter. Conversely, the organic HPs unveil a stronger interaction with photocarriers resulting in more significant yet elastic distortion, with MAPbBr 3 exhibiting up to 0.3% change. We demonstrate the modality of this distortion by varying the excitation power over 20 distinct states and cycles, highlighting the suitability of HPs as building blocks for electrostriction devices. Our findings represent a key step toward establishing HPs as ideal platforms for optical and strain‐driven switchable photonic devices.