Suppressing intrinsic self-doping of CsPbIBr2 films for high-performance all-inorganic, carbon-based perovskite solar cells

CsPbIBr2 is promising for all-inorganic, carbon-based perovskite solar cells (PSCs), owing to its quite balanced bandgap and stability characteristics. However, the serious self-doping phenomenon in one-step solution-processed CsPbIBr2 films that causes decreased built-in potentials (Vbis) and intensified carrier recombination hinders further performance optimization of the resulting PSCs. Herein, we demonstrate that such an obstacle can be overcome through rationally tailoring CsPbIBr2 precursor stoichiometry. Experimental results consistently show that a PbBr2-rich precursor tends to reinforce self-doping in the CsPbIBr2 film, while a CsI-rich one helps to weaken it. Thus, CsPbIBr2 films with a much lower self-doping level are achieved based on the CsI-rich precursor with an optimized CsI/PbBr2 stoichiometric ratio of 1.1 : 1.0. The films possess a pure phase, much fewer compositional defects, and increased work function, resulting in suppressed carrier recombination and extended Vbi of the final PSCs. Consequently, their average efficiency is boosted to (9.92 ± 0.56)%, far exceeding those of films fabricated with a stoichiometric precursor with the value of (8.32 ± 0.61)%. Particularly, the champion CsPbIBr2 PSC delivers a superior efficiency of 10.48% and an outstanding photovoltage of 1.32 V. This work represents a major leap for CsPbIBr2 PSCs and paves the way for their further exploration to achieve better performance.