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 CH 3 NH 3 PbI 3 . A small amount of H 2 O was added into PbI 2 /DMF to make a homogenous precursor solution. A high quality PbI 2 film with full coverage was formed on a PEDOT:PSS surface by spin coating of the homogeneous PbI 2 precursor solution. The perovskite film fabricated from the high quality PbI 2 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 PbI 2 /DMF solution may affect the properties of PbI 2 and therefore the perovskite film prepared using the two-step method and the overall photovoltaic performance of the corresponding inverted solar cell.

A two-step spin-coating process was used to synthesize perovskite films at ambient conditions. Combining a PEDOT:PSS hole-transport layer and a PC71BM acceptor, the device achieves a power conversion efficiency of 16.31% with a remarkably highVocof 1.05 V and FF of 0.78.

No abstract

Sputtering made ZnO thin film was used as an electron-transport layer in a regular planar perovskite solar cell based on high quality CH3NH3PbI3 absorber prepared with a two-step spin-coating. An efficiency up to 15.9% under AM 1.5G irradiation is achieved for the cell based on ZnO film fabricated under Ar working gas. The atmosphere of the sputtering chamber can tune the surface electronic properties (band structure) of the resulting ZnO thin film and therefore the photovoltaic performance of the corresponding perovskite solar cell. Precise surface engineering of ZnO thin film was found to be one of the key steps to fabricate ZnO based regular planar perovskite solar cell with high power conversion efficiency. Sputtering method is proved to be one of the excellent techniques to prepare ZnO thin film with controllable properties.