Elucidation of Perovskite Film Micro-Orientations Using Two-Photon Total Internal Reflectance Fluorescence Microscopy

The emergence of efficient hybrid organic-inorganic perovskite photovoltaic materials has brought about the rapid development of a variety of preparation and processing techniques designed to maximize their performance. As processing methods continue to emerge, it is important to understand how the optical properties of these materials are affected on a microscopic scale. Here, polarization-resolved two-photon total internal reflectance microscopy (TIRFM) was used to probe changes in transition dipole moment orientation as a function of thermal annealing time in hybrid organic-inorganic lead-iodide-based perovskite (CH₃NH₃PbI₃) thin films on glass. These results show that as thermal annealing time is increased the distribution of transition moments pointing out-of-plane decreases in favor of forming areas with increased in-plane orientations. It was also shown through the axial sensitivity of TIRFM that the surface topography is manifested in the signal intensity and can be used to survey aspects of morphology in coincidence with the optical properties of these films.