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 (CsPbBr3) 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 CsPbBr3 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 CsPbBr3/carbon is implemented to passivate perovskite surface defect states and also to improve energy-level alignment between the valence band of CsPbBr3 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-TiO2/m-TiO2/CsPbBr3/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 CsPbBr3 PSCs.