Vapor-phase iodine emission and Ag surface accumulation in perovskite solar cells

The origin and time-dependent behavior of iodine detected on Ag electrodes in perovskite solar cells were investigated using X-ray photoelectron spectroscopy. Iodine was present at the Ag surface and near the Ag/hole transport layer interface, but no significant signal was observed in bulk Ag. Surface iodine increased within the first few days after fabrication and continued to rise over several weeks. Surface iodine accumulation was also observed on Ag films stored in the same container without direct contact with the perovskite devices. These results are consistent with volatile iodine-containing species released from the perovskite layer and re-adsorbing on Ag.