Low-temperature solution-processed NiOx films for air-stable perovskite solar cells

The use of organic hole transporting layers (HTLs) in organolead halide perovskite solar cells (PSCs) often limits the air and thermal stability of the devices. In this work, we developed a low-temperature solution process that enables the fabrication of nickel oxide (NiOx) based HTLs on top of perovskite active layers. The NiOx film exhibits a uniform and dense morphology, rendering the PSCs air-stable and thermally stable. We further found that by introducing an interfacial layer (e.g. CuSCN) between the NiOx film and the top metal electrode, the power conversion efficiency (PCE) of the PSCs can be largely improved from 10.4% to 17.2%, while the air stability continues to be excellent. The role of the interfacial layer was investigated through impedance analysis and ultraviolet photoelectron spectroscopy. Remarkably, the PSCs with the NiOx/CuSCN hybrid inorganic HTL exhibit no degradation in their PCE after being exposed to ambient air (humidity level: 50–60%) for 4 months without encapsulation.