Influence of Deposition and Annealing Parameters on the Degradation of Spray-Deposited Perovskite Films

In this work, CH3NH3PbI3 perovskite thin films were deposited by the spray-coating method in ambient conditions using different deposition temperatures and annealing times. They were then exposed to high humidity in order to investigate the relation between processing parameters and degradation mechanisms. FTIR and XRD analyses identified two degradation mechanisms, one reversible, the formation of monohydrated perovskite, CH3NH3PbI3∙H2O, and another irreversible, the decomposition of perovskite into PbI2 and CH3NH3I. It was found that perovskite degradation is very sensitive to deposition parameters and that long annealing times at high temperatures increase compound stability, retarding reversible degradation even after a long exposure to ambient conditions. This is attributed to the formation of a small amount of PbI2 during deposition that acts as a protective layer against moisture, preventing the formation of monohydrated perovskite. Additionally, no signs of dihydrated perovskite were found in the films even after 50 days of exposure to high humidity.