Polymer-Passivated Inorganic Cesium Lead Mixed-Halide Perovskites for Stable and Efficient Solar Cells with High Open-Circuit Voltage over 1.3 V.

Cesium-based trihalide perovskites have been demonstrated as promising light absorbers for photovoltaic applications due to its superb composition stability. However, the large energy losses (Eloss) in the conversion from photons to electrons observed in many inorganic perovskite solar cells has become a major hindrance impairing the ultimate efficiency of these devices. Here, we report an effective and reproducible method of modifying the interface between a CsPbI2Br absorber and polythiophene hole-acceptor to minimize the Eloss. We demonstrate that polythiophene, deposited on the top of CsPbI2Br, can significantly reduce electron-hole recombination within the perovskite, which is due to the electronic passivation of surface defect states. In addition, the interfacial properties are improved by a simple annealing process, leading to significantly reduced energy disorder in polythiophene and enhanced hole-injection into the hole-acceptor. Consequently, one of the highest power conversion efficiency (PCE) of 12.02% from a reverse scan in stable inorganic mixed-halide perovskite solar cells is obtained under 100 mW cm-2 AM1.5G solar illumination. Modifying the perovskite films with annealing polythiophene enables an open-circuit voltage (VOC) of up to 1.32 V, which is the highest value reported among cesium-lead mixed-halide perovskite solar cells. The Eloss of 0.5 eV is one of the lowest voltage deficits reported among inorganic perovskite photovoltaics to date. This method provides a new route to further improve the efficiency of perovskite solar cells by minimizing the Eloss