Heat- and gas-induced transformation in CH3NH3Pbl3 perovskites and its effect on the efficiency of solar cells

Following the remarkable success of the application of CH3NH3PbI3 perovskites in photovoltaics, a great focus has been placed on their stability to improve their optoelectronic properties and seek commercial production. To gain a better understanding of their thermal stability, we investigated the chemical, morphological, and photovoltaic transformations of CH3NH3PbI3 perovskites under elevated temperatures and various controlled atmospheric conditions (vacuum, 1 mbar O2, and 1 mbar H2O). A temperature-dependent study showed that CH3NH3PbI3 decomposed to PbI2 with the release of CH3NH2 and HI under low-temperature annealing (25–150 °C). Further annealing resulted in the formation of metallic lead (Pb0) under vacuum and Pb oxides and hydroxides under an O2 or H2O pressure. Moreover, the sublimation of Pb-based compounds occurred at temperatures above 150 °C, causing structural changes, which resulted in a decrease in the power conversion efficiency of the solar cell. A time-dependent study showed that, compared with vacuum conditions, the addition of O2 or H2O accelerated the degradation of the perovskite films.