High efficiency stable inverted perovskite solar cells without current hysteresis

The inverted perovskite solar cell fabricated using a two-step method exhibited the highest FF of 0.85 and good efficiency of 18% based on CH₃NH₃PbI₃. A small amount of H₂O was added into PbI₂/DMF to make a homogenous precursor solution. A high quality PbI₂ film with full coverage was formed on a PEDOT:PSS surface by spin coating of the homogeneous PbI₂ precursor solution. The perovskite film fabricated from the high quality PbI₂ film is highly pure, smooth and very dense even without any pinhole. The champion cell achieves a remarkable fill factor (FF) of 0.85, which is the highest value reported in perovskite solar cells. The FF value is also very reproducible with less than 10% deviation for 50 cells. The cell exhibits no current hysteresis and is stable under both dark and illumination conditions in dry and inert atmospheres. The results not only provide a strategy to fabricate high efficiency inverted perovskite solar cells but also reveal how the water additive in the PbI₂/DMF solution may affect the properties of PbI₂ and therefore the perovskite film prepared using the two-step method and the overall photovoltaic performance of the corresponding inverted solar cell.