Hysteresis free low temperature processed planar perovskite solar cells with 19.1% efficiency
Hysteresis free, highly efficient and stable perovskite solar cells processed at low temperatures are strongly demanded to realize flexible or perovskite based tandem solar cells. Here, we report a hysteresis free planar CH3NH3PbI3 perovskite solar cell with a power conversion efficiency of 19.1% using a room temperature vacuum processed C60 electron transport layer (ETL) without the hole blocking layer. By optimizing the thickness of the C60 layer, the highly homogeneous, uniform, and dense ETL with a thickness of 35 nm is found to not only passivate the grain boundaries and surfaces of the perovskite layer, but also enhance charge transport properties. Thus, the C60 layer deposited on perovskites eliminates the photocurrent hysteresis and improves the cell efficiency. Also, compared to the device adopting the C60 and bathocuproine (BCP) combination, the one with the C60 layer without the BCP layer shows better performance due to enhanced electron extraction properties. Furthermore, for the first time, we have demonstrated a hysteresis free flexible perovskite solar cell using the C60 ETL on a polyethylene naphthalate (PEN) substrate with 16.0% efficiency.