Lead iodide as a buffer layer in UV-induced degradation of CH3NH3PbI3 films

•Accelerated tests of photostability of CH3NH3PbI3 films using concentrated sunlight.•Unreacted PbI2 near the substrate in CH3NH3PbI3 films may enhance their photostability.•The preparation method is significant in determining the photostability of CH3NH3PbI3.•CH3NH3PbI3 degradation is induced by UV irradiation even in the absence of TiO2.