16.10% Carbon-Based Hole-Transport-Layer-Free CsPbI2Br Solar Cells Enabled by Uracil-Based Additives

Carbon-based hole-transport-layer (HTL)-free CsPbI 2 Br solar cells present a promising balance among efficiency, stability and cost. Nevertheless, their performance is still restricted by bulk and interfacial defects, as well as energy level mismatch between CsPbI 2 Br and its neighboring layers. Herein, a series of uracil-based additives, including uracil, 5-cyanouracil (5-CU) and 5-nitrouracil (5-NU), are introduced into CsPbI 2 Br to construct dipolar molecular bridges that can simultaneously passivate defects (i.e., uncoordinated Pb 2+ and mobile halide ions in CsPbI 2 Br and uncoordinated Sn 4+ on the surface of SnO 2 ), improve crystallinity, and regulate interfacial energy level alignment. It is further found that the most polar 5-NU exhibits the best ability to realize these functions. The 5-NU-optimized device thus achieves a leading power conversion efficiency of 16.10%, with an exceptional open-circuit voltage of 1.345 V, significantly reduced hysteresis and excellent operational stability.