Wavelength Dependent Photostability of Perovskite Thin Films

In the ten years since their first reported use in a photovoltaic device, hybrid organic-inorganic perovskite solar cell’s power conversion efficiencies have surpassed 25% and further research efforts have continued to improve their scalability and long-term operational stability. One stability that has to be thoroughly investigated is the long term photostability of the perovskite materials. Here we will present our recent in-situ wavelength-dependent photostability investigation on bare perovskite thin films. Pristine co-evaporated CH₃NH₃PbI₃ thin films were initially grown on pyrolytic graphite surfaces, and they were then illuminated for prolonged durations to approximately 1 sun (1mW/mm²) of either blue (408 nms) or red (650 nms) laser light. The films were maintained under constant vacuum conditions, and x-ray photoemission spectroscopy measurements were taken after each exposure. The dichotomy of the behavior of the films while under either the red or blue light, is suggestive of a wavelength dependence to the degradation mechanisms.