Oxidation State Manipulation of NiO_x for High Performance and Light-Soaking Stability of Perovskite Solar Modules

NiO_x is widely used for hole-transporting layers in p-i-n-type perovskite solar cells (PSCs) due to its stability, wide bandgap (≈3.5 eV), and solution processability. However, during solution processing, oxygen exposure can induce non-stoichiometry, forming Ni^{≥3 +}. While Ni^{≥3 +} enhances hole mobility, it also promotes redox reactions at the interface, undermining long-term stability. To utilize the improved mobility without sacrificing stability, bilayer NiO_x films with controlled Ni^{≥3 +} concentrations can be fabricated. Sputtering is ideal for this, enabling precise control of oxygen partial pressure during deposition. This study utilizes sputtering to regulate Ni^{≥3 +} levels and optimize the ratio of two NiO_x layers in bilayer films, improving charge extraction and transport. A fabricated perovskite module with a 16.0 cm² aperture area achieves a photo-conversion efficiency (PCE) of 16.5%. Additionally, the module retains 80% of its initial PCE after 1000 h under continuous 1-sun illumination, thanks to the stable bilayer NiO_x structure.