Photoplastic effect in organic–inorganic lead iodide perovskite thin films

The positive photoplastic effect (PPE) and photoinduced stiffening are the reversible increases of the flow stress and the elastic modulus of a material upon irradiation with light. Several material groups, including the II-VI compounds and alkali halides show some form of these effects. The dependence of mechanical properties on light illumination has not been reported for methylammonium lead iodide (CH3NH3PbI3 or MAPbI3) perovskites. In this study a positive PPE and photoinduced stiffening were found in MAPbI3 thin film perovskites. Thin films of 500 nm thickness were synthesized and then polished. The chemical formation of MAPbI3 was verified by x-ray diffraction. Atomic force microscopy and scanning electron microscopy were used to characterize the surface topography. Nanoindentation experiments were performed to investigate the elastic and plastic properties in darkness and under illumination. The elastic modulus and hardness were found to increase by 53% and 67% respectively when the perovskite was illuminated.