Lattice Modulation of Alkali Metal Cations Doped Cs1−xRxPbBr3 Halides for Inorganic Perovskite Solar Cells

The crystal structure of cesium lead halide (CsPbX3, X = I, Br, Cl) determines its charge‐carrier trap state and solar‐to‐electrical conversion ability in inorganic perovskite solar cells (PSCs). Here, the compositional engineering of inorganic CsPbBr3 perovskite by means of doping with various alkali metal cations is studied. The lattice dimensions and energy levels of Cs1‐xRxPbBr3 (R = Li, Na, K, Rb, x = 0–1) halides are optimized by tuning Cs/R ratio. Arising from promoting effects of alkali metal cations doped perovskite halides such as lattice shrink, crystallized dynamics, and electrical‐energy distribution, a maximum power conversion efficiency as high as 9.86% is achieved for hole transporting layer‐free Cs0.91Rb0.09PbBr3 tailored solar cell owing to the suppressed non‐radiative losses and radiative recombination. Furthermore, the all‐inorganic Cs0.91Rb0.09PbBr3 solar cell without encapsulation remains 97% of initial efficiency when suffering persistent attack by 80% RH in air atmosphere over 700 h, which is in comparable with state‐of‐the‐art organic–inorganic hybrid and all‐inorganic PSC devices. Employing alkali metal cations to modulate perovskite layers provide new opportunities of making high‐performance inorganic PSC platforms. The lattice of inorganic CsPbBr3 halide is modulated by doping alkali metal cations to form Cs1−xRxPbBr3 (R = Li, Na, K, Rb, x = 0–1) perovskites. Through tuning R/Cs ratio, a PCE up to 9.86% and improved stability in 80% humidity are achieved for HTL‐free Cs0.91Rb0.09PbBr3 solar cell.