Bifunctional NiOx/Perovskite Interface Engineering for Efficient Air-Processed Wide-Bandgap Perovskite Solar Cells

Nickel oxide (NiO x ) hole transport layers are widely employed in perovskite solar cells (PSCs) due to their excellent chemical stability. However, the poor quality of the NiO x /perovskite interface limits device performance. Herein, we report a bifunctional interface engineering strategy using ammonium thiocyanate (NH 4 SCN) that reduces energy barriers and passivates defects at the NiO x /perovskite interface. NH 4 SCN decreases surface hydroxyl groups on NiO x , suppresses trap states, and improves energy-level alignment of hole transport layer with perovskite. Additionally, NH 4 SCN promotes the growth of larger perovskite grains, alleviates lattice strain, and passivates defects at buried interface of perovskite film, thus enhancing film quality and improving carrier lifetime. As a result, air-processed wide-bandgap PSCs based on NH 4 SCN-treated NiO x achieve a power conversion efficiency of 21.41% and an open-circuit voltage of 1.260 V, outperforming control devices (19.81%, 1.236 V). This work provides an effective interface engineering strategy for high-performance wide-bandgap PSCs.