Halide perovskites under polarized light: Mode symmetry analysis using ultralow frequency Raman

Hybrid organic-inorganic halide perovskites (HOPs) have shown exceptional potential for next generation photovoltaics and optoelectronics. Unlike conventional semiconductors (e.g. Si and GaAs), the opto-electronic properties of HOPs are strongly coupled to the anharmonic structural fluctuations. Therefore, it is crucial to understand the nature of atomic motions within the crystal. This has been challenging due to low thermal stability, strong light absorption and complex, temperature-dependent structural phase sequence of the HOPs. Here, we try to overcome these challenges and provide a detailed analysis of the Raman active mode symmetries in the low-temperature orthorhombic phase of methylammonium-lead iodide. Raman measurements using linearly and circularly polarized 1.16 eV excitation laser (to prevent thermal damage) are combined to elucidate the effects of birefringence on the Raman signal. These results provide a deeper understanding of the interaction of HOPs with polarized light which can play a key role in HOP based device design.