Optical monitoring of CH3NH3PbI3 thin films upon atmospheric exposure

CH3NH3PbI3 perovskite films of interest for photovoltaic (PV) devices have been prepared by (i) vapor deposition and (ii) solution processing. Complex dielectric function (epsilon = epsilon(1) + i epsilon(2)) spectra and structural parameters of the films have been extracted using near infrared to ultraviolet spectroscopic ellipsometry. In situ real time spectroscopic ellipsometry (RTSE) over a 48 h period has been performed on vapor deposited CH3NH3PbI3 after the deposition in normal atmospheric laboratory ambient conditions. Analysis of RTSE data for vapor deposited CH3NH3PbI3 film prepared under un-optimized conditions identifies phase segregated PbI2 and CH3NH3I at the substrate/film interface and unreacted PbI2 and CH3NH3I on the film surface. This analysis also provides the time dependence of the effective thicknesses of perovskite film, unreacted components, and phase segregated layers to track CH3NH3PbI3 decomposition.