A Semitransparent Inorganic Perovskite Film for Overcoming Ultraviolet Light Instability of Organic Solar Cells and Achieving 14.03% Efficiency

Abstract Organic solar cells (OSCs) can be unstable under ultraviolet (UV) irradiation. To address this issue and enhance the power conversion efficiency (PCE), an inorganic‐perovskite/organic four‐terminal tandem solar cell (TSC) based on a semitransparent inorganic CsPbBr 3 perovskite solar cell (pero‐SC) as the top cell and an OSC as bottom cell is constructed. The high‐quality CsPbBr 3 photoactive layer of the planar pero‐SC is prepared with a dual‐source vacuum coevaporation method, using stoichiometric precursors of CsBr and PbBr 2 with a low evaporation rate. The resultant opaque planar pero‐SC exhibits an ultrahigh open‐circuit voltage of 1.44 V and the highest reported PCE of 7.78% for a CsPbBr 3 ‐based planar pero‐SC. Importantly, the devices show no degradation after 120 h UV light illumination. The related semitransparent pero‐SC can almost completely filter UV light and well maintain photovoltaic performance; it additionally shows an extremely high average visible transmittance. When it is used to construct a TSC, the top pero‐SC acting as a UV filter can utilize UV light for photoelectric conversion, avoiding the instability problem of UV light on the bottom OSC that can meet the industrial standards of UV‐light stability for solar cells, and leading to the highest reported PCE of 14.03% for the inorganic‐perovskite/organic TSC.