The Impact of Atmosphere on Energetics of Lead Halide Perovskites

Solar cells based on metal halide perovskites have emerged as a promising low-cost photovoltaic technology. In contrast to inert atmospheres where most of the lab-scale devices are made to date, large-area low-cost production of perovskite solar cells often involves processing of perovskites in various atmospheres including ambient air, nitrogen, and/or vacuum. Herein, the impact of atmosphere on the energy levels of methylammonium lead halide perovskite films is systematically investigated. The atmosphere is varied to simulate the typical fabrication process. Through a comprehensive analysis combining the Fermi level evolution, surface photovoltage, photoluminescence properties, photovoltaic performance, and device simulation, an overall landscape of the energy diagram of the perovskite layer is able to be determined. The findings have direct implications for real-world devices under typical atmospheres, and provide insights into the fabrication-process design and optimization. Furthermore, a universal Fermi level shift under vacuum for lead halide-based perovskites revealed in this study, urges a refreshed view on the energetics studies conducted without considering the atmospheric effect.