Composition engineering of operationally stable CsPbI₂Br perovskite solar cells with a record efficiency over 17%

Despite the rapid progress in inorganic cesium lead halide perovskite (CsPbX₃) materials originating from excellent thermal stability; their poor phase stability at room temperature and lower efficiency compared to organic-inorganic counterparts still limit their development toward commercialization. Recently, Pb-site doping of inorganic perovskites stand outs for the improvement of aforementioned issues for emerging photovoltaic applications. Herein, we introduce a compositional engineering approach to tune the CsPbI₂Br crystallization by directly incorporating iron (II) chloride (FeCl₂) into perovskite precursor. The small amount of FeCl₂ stabilizes the black α-phase to avoid the undesirable formation of the non-perovskite phase owing to Fe²⁺ induced grain size reduction. Besides, the FeCl₂ incorporation thoroughly align the energy level, promote the built-in potential (V_bi), and reduce the defect states in the perovskite, resulting in a record power conversion efficiency (PCE) of 17.1% with a remarkable open-circuit voltage (V_OC) of 1.31 V. More importantly, FeCl₂-doped CsPbI₂Br-based devices exhibit an exceptional operational stability with a retention of over 95% initial PCE after 330 h at maximum power point (MPP) tracking.