Interfacial modification between NiOx and perovskite layers with hexafluorophosphate salts for enhancing device efficiency and stability of perovskite solar cells

Abstract

Inorganic metal oxides like nickel oxides (NiO_x) have been largely adopted as hole transport layers (HTLs) for the fabrication of perovskite solar cells (PSCs). Reducing interfacial defects between the NiO_x HTL and the perovskite absorbing layer is always a key issue in achieving high efficiency and long-term stability of PSCs. In this work, we first utilized inorganic hexafluorophosphate salts including NH₄PF₆, LiPF₆, and NaPF₆ to modify the surface of NiO_x through interactions between Ni atoms and PF₆⁻ groups. The incorporation of those salts not only decreased the defects at the NiO_x/perovskite interface but also optimized the energy levels of NiO_x to match with the perovskite. After the surface passivation of NiO_x, the up-lying perovskite consequently exhibited larger grain sizes and shorter carrier lifetime. The PSC based on an NH₄PF₆-modified NiO_x HTL showed the best efficiency of 17.28% and a long device lifetime of over 108 days, which was significantly better than the controlled device using the pristine NiO_x layer. Our experimental results demonstrate that interface modification of NiO_x by hexafluorophosphate salts is an effective strategy to optimize the performance of PSCs.