Researchers at the University of California (UC Davis) and Empa have shown that single-crystal halide perovskites can reversibly change their lattice under above-bandgap light excitation and elastically return to their original structure when the light is removed. This light-driven, hysteresis-free lattice response highlights soft-lattice halide perovskites as promising candidates for light-controlled semiconductor and strain-engineered devices.
Mechanically and chemically modulated strain in monocrystalline halide perovskites (HPs) has already been shown to improve stability and phase purity, but the interplay between photoexcitation-driven lattice distortions, strong electron-phonon coupling, and A-site cation dynamics has not been fully clarified. In this study, transient lattice distortions were measured in single-crystal MAPbBr3, FAPbBr3, and CsPbBr3 in response to above-bandgap light excitation using an X-ray probe to directly monitor structural changes. The measurements reveal reversible, hysteresis-free photoinduced lattice distortion: when light is applied, the internal lattice parameters shift, and when the light is turned off, the crystals recover their initial structure, and this cycle can be repeated many times.
The distortion amplitude depends on the pump power, with CsPbBr3 showing the highest resilience against lattice deformation, at a maximum change of 0.062% in the out-of-plane lattice parameter, while MAPbBr3 exhibits up to a 0.3% change, indicating a much stronger, yet still elastic, interaction between photocarriers and the organic-inorganic lattice.
The response is not simply binary but tunable. By varying the excitation power over 20 distinct states and cycles, the researchers demonstrate a smooth evolution of lattice strain that can be scaled with light intensity. Both the color and intensity of the light influence the strength of the shape change, and different perovskite compositions - through their distinct bandgaps - respond differently to light, especially at frequencies above the bandgap. In other words, the photostrictive response can be adjusted like a “dimmer,” depending on how the material is composed and how it is illuminated.
These results establish halide perovskites as “smart materials” that can be tuned to respond to a stimulus in a controllable way, where light acts as the control input for reversible lattice distortion. Demonstrating elastic, repeatable, photoinduced strain in MAPbBr3, FAPbBr3, and CsPbBr3 under well-defined excitation conditions can be a step toward exploiting HPs as building blocks for electrostriction devices and for optical and strain-driven switchable photonic devices.
