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

Abstract

The PF 6 − groups interact with Ni atoms to tightly attach to the NiO x layer, resulting in enhanced carrier extraction of NiO x . 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 NH 4 PF 6 , LiPF 6 , and NaPF 6 to modify the surface of NiO x through interactions between Ni atoms and PF 6 − 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 NH 4 PF 6 -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.