Anomalous p-type characteristic and recrystallization upon aging of hot-cast CH3NH3PbI3 perovskite thin films grown under atmospheric air

Hot-cast CH3NH3PbI3 perovskite thin films are fabricated in ambient air using heated substrates. All the
perovskite films prepared are stored in a low-humidity environment. Interestingly, it has been observed that the
perovskite films fabricated with high-temperature substrates degrade at a slower rate compared to those pre pared at lower temperatures. Even after one week, the morphology of the films remains unchanged when pro duced with high-temperature substrates under 35–40 % relative humidity (RH). The hot-cast films exhibit p-type characteristics, as evidenced by their surface photovoltage signals. During the aging process, the iodine ions seem to vaporize as evidenced by the reduction of the I/Pb ratios in the energy-dispersive X-ray spectroscopy (EDX) spectra. The hot-cast perovskite films show relatively low surface trap states, ranging from 1015–1016 cm3, along with low energy band tails of approximately 20 meV.