Oxidized Nickel to Prepare an Inorganic Hole Transport Layer for High-Efficiency and Stability of CH₃NH₃PbI₃ Perovskite Solar Cells

In this study, we report a perovskite solar cell (PSC) can be benefited from the high quality of inorganic nickel oxide (NiO_x) as a hole transport layer (HTL) film fabricated from the physical vapor deposition (PVD) process. The power conversion efficiency (PCE) of PSC is found to depend on the thickness of NiO_x HTL. The NiO_x thickness is optimized via quantitative investigation of the structure, optical and electrical properties. With an active area of 11.25 cm², a PSC module (25 cm²) with a PCE of 15.1% is demonstrated, while statistically averaged PCE = 18.30% with an open voltage (V_oc) 1.05 V, short-circuit current density (J_sc) 23.89 mA/cm², and fill factor (FF) 72.87% can be achieved from 36 devices with smaller active areas of 0.16 cm². After the stability test at 40% relative humidity (RH) and 25 ^◦C for 1200 h, the highest performance NiO_x-based PSC is shown to be about 1.2–1.8 times superior to PEDOT:PSS organic HTL based PSC at the same environment.