- Encapsulated CH 3 NH 3 PbI 3 films, the 'work horse' of the organic-inorganic perovskite-based photovoltaics, grown by one step-and two step-deposition methods, were used to study the effect of the film preparation method on their photostability. Time dependent light absorption decay under exposure to concentrated sunlight was used to estimate the degradation of the films. Films deposited by one step showed a significant decrease in the CH 3 NH 3 PbI 3 absorbance when illuminated through the substrate, while films obtained through two step deposition exhibited almost no photodegradation under similar sunlight exposure. On the other hand, both types of films degraded significantly when irradiated through the top encapsulation. Unreacted PbI 2 present near the substrate is suggested to be responsible for enhancing the photostability of the films obtained by two step deposition. Here, remnant PbI 2 works as a UV filter and reduces UV light-induced degradation. The results demonstrate the significance of the preparation method in determining photochemical stability of the perovskite films, due to favorable property of remnant PbI 2 in the absorber as a UV-protective layer.