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

Abstract

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.

Keywords:
Perovskite films; reversible and irreversible degradation; spray deposition