Selective Crystallization Delay in Wide‐Bandgap Perovskites Enables Initial Homogeneous Phase for Square Centimeter Perovskite/Organic Tandem Solar Cells

Abstract Mixed halide wide‐bandgap (WBG) perovskites, used in high‐performance perovskite/organic tandem solar cells (TSCs), are prone to phase segregation under light irradiation. Particularly, the initial inhomogeneous halide phase distribution in WBG perovskites can accelerate the phase segregation under operational stressors, thus hindering scaling of TSCs that require high phase homogeneity. Here, a selective delayed crystallization strategy is proposed in which a functional agent (3‐amino‐5‐fluorobenzamide; AFBA) is used to regulate the initial halide phase distribution. The ‐NH 2 of AFBA, with a low electron‐cloud density, shows a higher binding affinity with bromide than with iodide, thus selectively delaying the rapid crystallization of bromide; this phenomenon induces a homogeneous halide distribution across the film. The initial homogeneous film is phase‐stable under operational stressors. As a result, the square‐centimeter WBG perovskite front cell achieves a high efficiency of 18.61%. When stacked with organic subcells, the square‐centimeter perovskite/organic TSC exhibits a remarkable efficiency of 25.21%, showing a weak‐dependence of efficiency on size from 0.062 to 2.000 cm 2 , as well as a prolonged operational lifetime with a T 90 of 1500 h. Perovskite/organic TSCs are also connected in series with electrochromic devices to dynamically monitor the TSC performance via the color variation, providing insights for their future applications.