REMNANT LEAD IODIDE AS A BUFFER LAYER FOR IMPROVED PHOTOSTABILITY OF CH₃NH₃PbI₃ FILMS

One- and two step- deposition methods of the metal halide perovskite CH₃NH₃PbI₃ were explored in terms of the effect of the preparation method on the photostability of encapsulated CH₃NH₃PbI₃ films. Photodegradation study was carried by following the light absorption decay under exposure to concentrated sunlight. Films deposited by the two step method showed better stability than those deposited by the one-step method when illuminated through the substrate. However, both types of films were found to be significantly photo-unstable when irradiated through the top encapsulating glass plate. It is assumed that unreacted PbI₂ present in the perovskite film near the substrate is responsible for enhancing the photostability of the films obtained by two step deposition. This was confirmed by characterization of the film using grazing angle XRD. We postulate that remnant PbI₂ works as a UV filter/absorber and reduces UV-induced photodegradation of CH₃NH₃PbI₃. The results demonstrate the additional benefit of the two step preparation method in increasing the photochemical stability of perovskite films.