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

Abstract

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 (V_bis) 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 V_bi 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.