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

Abstract

Cesium-based trihalide perovskites have been demonstrated as promising light absorbers for photovoltaic applications due to their superb composition stability. However, the large energy losses (E_loss) observed in inorganic perovskite solar cells has become a major hindrance impairing the ultimate efficiency. Here, an effective and reproducible method of modifying the interface between a CsPbI₂Br absorber and polythiophene hole-acceptor to minimize the E_loss is reported. It is demonstrated 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 inorganic mixed-halide perovskite solar cells is obtained. Modifying the perovskite films with annealing polythiophene enables an open-circuit voltage (V_OC) of up to 1.32 V and E_loss of down to 0.5 eV, which both are the optimal values reported among cesium-lead mixed-halide perovskite solar cells to date. This method provides a new route to further improve the efficiency of perovskite solar cells by minimizing the E_loss.

The interfacial properties between CsPbI₂Br absorber and poly(3-hexylthiophene) (P3HT) hole-acceptor are improved by passivating the surface defects of CsPbI₂Br and reducing the energy disorder of P3HT. Consequently, a stable inorganic perovskite solar cell with high power conversion efficiency of 12.02% and minimal energy loss of 0.50 eV is obtained.

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