Effect of intermediate phases on the optical properties of PbI2-rich CH3NH3PbI3 organic–inorganic hybrid perovskite

Abstract

Methylammonium lead halide perovskite (CH₃NH₃PbI₃) films, with high PbI₂ concentration, were grown by the two-step spin coating method. The influence of the precursor concentration and annealing time on the optical and structural properties of the perovskite films was analyzed by optical absorption, photoluminescence, X-ray diffraction and scanning electron microscopy. The results showed that, in addition to the CH₃NH₃PbI₃ and PbI₂ phases, intermediate phases, such as (MA)₂(DMF)₂Pb₃I₈, were formed in the films, depending on the time and temperature of annealing, which can tune the optical absorption in the visible spectra. This intermediate phase induced the formation of perovskite nanowires, identified by SEM images, and their growth may be associated with the presence of the DMF solvent remaining in the PbI₂ film.