A‐Site Rubidium Cation‐Incorporated CsPbI2Br All‐Inorganic Perovskite Solar Cells Exceeding 17% Efficiency

Due to its excellent thermal stability and high performance, inorganic cesium lead mixed halide (ABX 3 , where A = Cs, B = Pb, and X = I/Br) all‐inorganic perovskite solar cells (IPVSCs) have attracted much interest in optoelectronic applications. However, the film quality, enough absorption by desired film thickness, and nature of partial replacement of cations determine the stability of the CsPbI 2 Br perovskite films. Herein, a hot air method is used to control the thickness and morphology of the CsPbI 2 Br perovskite thin film, and the A‐site (herein, Cs + ) cation is partially incorporated by rubidium (Rb + ) cations for making the stable black phase under ambient conditions. The Rb cation‐incorporated Cs 1− x Rb x PbI 2 Br ( x = 0–0.03) perovskite thin films exhibit high crystallinity, uniform grains, extremely dense, and pinhole‐free morphology. The fabricated device with its Cs 0.99 Rb 0.01 PbI 2 Br perovskite composition with poly(3‐hexylthiophene‐2,5‐diyl) as a hole‐transporting layer exhibits a power conversion efficiency (PCE) of 17.16%, which is much higher than that of CsPbI 2 Br‐based IPVSCs. The fabricated Cs 0.99 Rb 0.01 PbI 2 Br‐based IPVSC devices retain >90% of the initial efficiency over 120 h at 65 °C thermal stress, which is much higher than that of CsPbI 2 Br samples.