Environmentally friendly, aqueous processed ZnO as an efficient electron transport layer for low temperature processed metal-halide perovskite photovoltaics

Here we report the incorporation of ZnO electron transport layers (ETLs), deposited using a remarkably simple water-based processing route, for use in methylammonium lead iodide (MAPI, CH3NH3PbI3) perovskite solar cells. The influence of ZnO processing temperature on the thermal stability and surface morphology of the perovskite films is studied in detail. We find that operational devices are achieved over the entire ZnO processing temperatures range investigated (100-450 degrees C) -however those prepared at 100 degrees C are significantly affected by current-voltage hysteresis. We find that the insertion of a thin phenyl-C-61-butyric acid methyl ester (PCBM) layer between the ZnO and the MAPI significantly reduces current-voltage (J-V) hysteresis. Additionally we determine that the thermal stability of the MAPI improves when PCBM is inserted as an interface modifier. The fabrication of the PCBM modified ZnO at 100 degrees C enables the formation of low-temperature processed, thermally stable normal architecture cells with negligible hysteresis.