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

Abstract An optimized two-step sequential deposition method to fabricate hole-transport-layer-free carbon-based methyl ammonium lead bromide (MAPbBr3) perovskite solar cells is reported. Small amounts of MABr are introduced into the PbBr2 precursor solution during the first step to prepare MAPbBr3 perovskite films (labeled as MAPB-xMABr), which promotes the conversion of PbBr2 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% (VOC = 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.