As a common inorganic hole transport layer material in high efficiency perovskite solar cells, nickel oxide (NiOx) has good optical transmission and chemical stability, and can also be prepared by magnetron sputtering and other scalable manufacturing methods at low cost. However, compared to organic hole transport materials, the energy level mismatch, defects, and adverse chemical reactions at the NiOx/perovskite interface deteriorate the performance of NiOx-based wide-bandgap perovskite solar cells (PSCs). To address these issues simultaneously, a self-assembled layer of (2-(9H-carbazol-9-yl) ethylphosphonic acid (2PACz) was proposed as NiOx/wide-bandgap perovskite interface modification material. This molecule can passivate NiOx surface traps, optimize the film formation of the upper perovskite layer and facilitate charge transport. Consequently, the power conversion efficiency (PCE) of wide-bandgap PSCs increase from 16.18% to 18.42%. This work provides a reference strategy for the application of NiOx hole transport layer in wide-bandgap PSCs.