Cu/CuO nanocomposite films as a p-type modified layer for efficient perovskite solar cells.

Cu/CuO films grown by ion beam sputtering were used as p-type modified layers to improve the efficiency and stability of perovskite solar cells (PSCs) with an n-i-p heterojunction structure. The ratio of Cu to CuO in the films can be tuned by the oxygen flow ratio (O/(O + Ar)) during the sputtering of copper. Auger electron spectroscopy was performed to determine the elemental composition and chemical state of Cu in the films. Ultraviolet photoelectron spectroscopy and photoluminescence spectroscopy revealed that the valence band maximum of the p-type Cu/CuO matches well with the perovskite. The Cu/CuO film not only acts as a p-type modified layer but also plays the role of an electron blocking buffer layer. By introducing the p-type Cu/CuO films between the low-mobility hole transport material, spiro-OMeTAD, and the Ag electrode in the PSCs, the device durability and power conversion efficiency (PCE) were effectively improved as compared to the reference devices without the Cu/CuO interlayer. The enhanced PCE is mainly attributed to the high hole mobility of the p-type Cu/CuO film. Additionally, the Cu/CuO film serves as a protective layer against the penetration of humidity and Ag into the perovskite active layer.