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

TLDR

Cesium‑based trihalide perovskites are promising light absorbers due to their composition stability, yet inorganic perovskite solar cells suffer large energy losses that limit their ultimate efficiency. The study reports an effective, reproducible method to modify the interface between a CsPbI₂Br absorber and a polythiophene hole‑acceptor to minimize energy loss. The interface is modified by depositing polythiophene onto CsPbI₂Br and applying a simple annealing step to reduce energy disorder and enhance hole injection. Polythiophene passivation and annealing of the CsPbI₂Br interface reduce recombination and energy disorder, yielding a record 12.02 % PCE, 1.32 V V_oc, and 0.5 eV energy loss, the best values reported for cesium‑lead mixed‑halide perovskite cells.

Abstract

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 CsPbI 2 Br absorber and polythiophene hole‐acceptor to minimize the E loss is reported. It is demonstrated that polythiophene, deposited on the top of CsPbI 2 Br, 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 .