Magnetron sputtered nickel oxide with suppressed interfacial defect states for efficient inverted perovskite solar cells

Widely used spin-coated nickle oxide (NiO_x) based perovskite solar cells often suffer from severe interfacial reactions between the NiO_x and adjacent perovskite layers due to surface defect states, which inherently impair device performance in a long-term view, even with surface molecule passivation. In this study, we developed high-quality magnetron-sputtered NiO_x thin films through detailed process optimization, and compared systematically sputtered and spin-coated NiO_x thin film surfaces from materials to devices. These sputtered NiO_x films exhibit improved crystallinity, smoother surfaces, and significantly reduced Ni³⁺ or Ni vacancies compared to their spin-coated counterparts. Consequently, the interface between the perovskite and sputtered NiO_x film shows a substantially reduced density of defect states. Perovskite solar cells (PSCs) fabricated with our optimally sputtered NiO_x films achieved a high power conversion efficiency (PCE) of up to 19.93% and demonstrated enhanced stability, maintaining 86.2% efficiency during 500 h of maximum power point tracking under one standard sun illumination. Moreover, with the surface modification using (4-(2,7-dibromo-9,9-dimethylacridin-10(9H)-yl)butyl)phosphonic acid (DMAcPA), the device PCE was further promoted to 23.07%, which is the highest value reported for sputtered NiO_x based PSCs so far.