Controlled Crystal Growth of All-Inorganic CsPbI2.2Br0.8 Thin Film via Additive Strategy for Air-Processed Efficient Outdoor/Indoor Perovskite Solar Cells

The evolution of defects during perovskite film fabrication deteriorates the overall film quality and adversely affects the device efficiency of perovskite solar cells (PSCs). We endeavored to control the formation of defects by applying an additive engineering strategy using FABr, which retards the crystal growth formation of CsPbI2.2Br0.8 perovskite by developing an intermediate phase at the initial stage. Improved crystalline and pinhole-free perovskite film with an optimal concentration of FABr-0.8M% additive was realized through crystallographic and microscopic analysis. Suppressed non-radiative recombination was observed through photoluminescence with an improved lifetime of 125 ns for FABr-0.8M% compared to the control film (83 ns). The champion device efficiency of 17.95% was attained for the FABr-0.8M% PSC, while 15.94% efficiency was achieved in the control PSC under air atmospheric conditions. Furthermore, an impressively high indoor performance of 31.22% was achieved for the FABr-0.8M% PSC under 3200 K (1000 lux) LED as compared to the control (23.15%). With a realistic approach of air processing and controlling the crystallization kinetics in wide-bandgap halide PSCs, this investigation paves the way for implementing additive engineering strategies to reduce defects in halide perovskites, which can further benefit efficiency enhancements in outdoor and indoor applications.