Advanced Modification of Perovskite Surfaces for Defect Passivation and Efficient Charge Extraction in Air-Stable CsPbBr3 Perovskite Solar Cells

An all-inorganic cesium lead bromide (CsPbBr 3 ) halide has attracted growing attention for carbon-based perovskite solar cells (PSCs) owing to its inherent stable lattice in thermal and/or moisture ambient. The main drawback for carbon-based CsPbBr 3 PSCs is the low power conversion efficiency (PCE) caused by serious charge recombination at perovskite surfaces and/or device interfaces. To address this problem, an interface engineering strategy by modifying a polyvinyl acetate (PVAc) polymer with a carbonyl group at the interface of CsPbBr 3 /carbon is implemented to passivate perovskite surface defect states and also to improve energy-level alignment between the valence band of CsPbBr 3 and work function of carbon, suppressing charge recombination and accelerating charge separation. By introducing the graphene oxide (GO) layer for further promoting hole extraction and decreasing energy-level difference, the PSC with an architecture of FTO/c-TiO 2 /m-TiO 2 /CsPbBr 3 /PVAc/GO/carbon achieves a champion PCE as high as 9.53%, yielding an improvement by 44.0% compared with 6.62% for the original device. Furthermore, the optimal device free of encapsulation exhibits remarkable long-term stability under high humidity, high temperature, and continuous illumination in air. This work provides a new polymer as the interface modification material for reducing defect states as well as enhancing energy-level alignment and suggests an effective approach for fabricating efficient and stable carbon-based CsPbBr 3 PSCs.