Precursor engineering for performance enhancement of hole-transport-layer-free carbon-based MAPbBr3 perovskite solar cells

An optimized two-step sequential deposition method to fabricate hole-transport-layer-free carbon-based methyl ammonium lead bromide (MAPbBr 3 ) perovskite solar cells is reported. Small amounts of MABr are introduced into the PbBr 2 precursor solution during the first step to prepare MAPbBr 3 perovskite films (labeled as MAPB-xMABr), which promotes the conversion of PbBr 2 into perovskite phase and results in denser perovskite films with increased crystallinity, lower trap density, and longer carrier lifetime. After optimization, a maximum power conversion efficiency (PCE) of 7.64% ( V OC  = 1.36 V) is obtained for MAPB-0.2MABr based solar cells. Significantly, the non-encapsulated devices exhibit excellent long-term stability in ambient air (25–30 °C and 20–30% relative humidity), showing no degradation after a year’s exposure. While, it also shows superior thermal stability with PCE retaining 95% of the initial efficiency after 120 h under thermal stress of 80 °C and 40–70% relative humidity.