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 C-60 electron transport layer (ETL) without the hole blocking layer. By optimizing the thickness of the C-60 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 C-60 layer deposited on perovskites eliminates the photocurrent hysteresis and improves the cell efficiency. Also, compared to the device adopting the C-60 and bathocuproine (BCP) combination, the one with the C-60 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 C-60 ETL on a polyethylene naphthalate (PEN) substrate with 16.0% efficiency.