Ambient-air crystallization of CsPbIBr2 films with polymer towards stable and efficient carbon-based perovskite solar cells

Cesium lead mixed-halide all-inorganic perovskite solar cells (PSCs) exhibit promising balance between the efficiency and environmental stability in contrast to hybrid PSCs. Nonetheless, they face challenges due to rapid crystallization of solution processed perovskite film, resulting in elevated lattice defect density and energy loss. Therefore, a hydrophobic long-chained polymer, polypropylene carbonate (PPC) is added in varying concentrations to CsPbIBr2 precursor solution to yield a good-quality film under ambient air and low-temperature conditions. Here, the 2 % PPC added film displayed improved crystallinity and morphology and large grain-size with passivated grain-boundaries. The absorption intensity of the film was largely enhanced with reduced charge recombination and tuned energy level alignment at perovskite/carbon interface which enhanced both efficiency and stability of hole-transport layer free C–IPSCs in ambient air (humidity∼ 65–70 %). The efficiency increased upto 7.36 % which is 62.4 % higher than the bare device, attributed to its increased photovoltage (1.17 V–1.25 V), current-density (8.42 mA cm−2 to 10.25 mA cm−2), and fill-factor (46 %–57.5 %). Furthermore, optimized device has a significantly longer lifetime than bare device. Hence, this work presents a simple strategy for developing commercially feasible PSCs.