Effects of domain size in polycrystalline perovskite organic-inorganic hybrids investigated by spatially resolved optical spectroscopy

We apply spatially resolved optical spectroscopy techniques, micro-Raman and micro-PL, to investigate individual perovskite single crystalline domains whose sizes are much larger than that of the diffraction limit laser spot, and compare the results to those of small polycrystalline domains with size below the laser spot size. The large and small domains show drastically different Raman and PL spectra, in terms of spectral features, intensity, and excitation density dependence. The excitation density dependence reveals possible local structural changes due to laser heating at relatively high illumination density. In addition, we also examine the changes in optical properties associated with the structural degradation of the perovskite - converting back to PbI2 after exposing the sample to air with humidity.