Oxidation State Manipulation of NiO x for High Performance and Light‐Soaking Stability of Perovskite Solar Modules

Abstract 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 cm 2 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.