Piezoreflectance: A sensitive method for studying optical and phase transitions in metal halide films

As the field of hybrid perovskites continues to expand, new methods to study their optical properties can enhance conventional approaches. In this study, we used piezo-modulation spectroscopy to investigate optical transitions in well-known perovskite films. A series of methylammonium and formamidinium perovskite layers via spin-coating and drop-casting directly onto a piezoceramic substrate were prepared. At room temperature, the piezoreflectance signal corresponding to optical transitions was successfully observed. To investigate the phase transitions in MAPbI3 in detail, measurements were performed over a wide temperature range for layers prepared using both drop-casting and spin-coating techniques. Complementary photoluminescence (PL) measurements served as a reference. The optical transition energies obtained from absorption-like (piezoreflectance) and emission-like (PL) experiments showed good agreement. The piezoreflectance method demonstrated higher sensitivity to phase transitions in standard MAPbI3 perovskite compared to PL due to its inherent sensitivity to structural phase transitions. This comparative analysis of the two techniques revealed that piezo-modulation spectroscopy provides valuable insights into the optical properties of MAPbI3 in halide perovskite semiconductors.