Elucidating the Failure Mechanisms of Perovskite Solar Cells in Humid Environments Using In Situ Grazing-Incidence Wide-Angle X-ray Scattering

The main downfall of perovskite solar cells is that they degrade rapidly when exposed to heat, light, and moisture. Although previous work has elucidated the decomposition pathways of lead halide perovskites, there has been little direct insight into how perovskite decomposition affects device performance. Therefore, in order to better understand this correlation, we performed in situ grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements on methylammonium lead iodide solar cells. We show that the formation of hydrate phases is not the most important device degradation pathway; rather, as water penetrates the cell, the mobility of iodide ions increases, leading to corrosion of the metallic top contact. Furthermore, the work reveals a temperature dependence to the perovskite decomposition pathway, with higher temperatures suppressing the formation of both intermediates and byproducts. The work suggests that the rigorous exclusion of moisture and the design of corrosion-resistant electrodes may help produce longer-lived perovskite solar cells.