ZnO/ZnS core-shell composites for low-temperature-processed perovskite solar cells

Electron transport layers（ETLs）in perovskite solar cells（PSCs）are a key factor to determine the photovoltaic performance.Herein,we demonstrate preparation of Zn O/ZnS core-shell composites through directly synthesizing ZnS on the ZnO nanoparticles in solution.We confirmed the formation of ZnO/ZnS core-shell composites by the uses of X-ray diffraction patterns and the Fourier transform infrared spectroscopy.ZnO/ZnS composites exhibit much homogeneous surface morphology as compared with the bare Zn O as revealed in the scanning electronic microscopy.Moreover,the upper shift of conduction band level upon composition of the Zn O/Zn S film results in a better alignment of energy level,which facilitates cascade charge extraction and thus improves the current density of perovskite solar cell.The shift of conduction band also improves the voltage of the PSCs.The photoluminescence（PL）spectroscopies measured in both steady and transient states were carried out to characterize the charge extraction at the interface between CH3NH3PbI3and the electron transport layers of either ZnO or ZnO/ZnS composite.The ZnO/ZnS composite can more efficiently quench the PL signal of perovskite absorber than bare Zn O resulting in enhanced photocurrent generation in PSCs.