Organic Salt Buffer Layer Enables High-Performance NiOx-Based Inverted Perovskite Solar Cells

The merits of a low-cost fabrication process, suitable band structure, excellent wettability to perovskite precursor, and outstanding stability ensure NiO_x as a hole transport material with beneficial characteristics to construct high-performance perovskite solar cells (PSCs). However, direct contact between perovskite and NiO_x causes delamination and chemical instability and thus results in poor carrier transport and short device lifespan. Here, we propose a solution for this issue by introducing an organic salt additive 4-(trifluoromethyl) benzylammonium formate (TFMBAFa) in the perovskite precursor to passivate perovskite film and NiO_x@(2-(3,6-dimethyl-9H-carbazol-9-yl) ethyl) phosphonic acid (Me-2PACz) composited hole transport layer (HTL), and thus construct a buffer layer between perovskite-HTL interface. The effective diminishing of NiO_x/perovskite interfacial reactions and defects results in enhanced carrier transport. Consequently, the target device achieves simultaneous improvements in power conversion efficiency (24.2%), storage stability (T100 > 1400 h), thermal stability (T80 > 1000 h), and operational stability (T70 > 850 h), where T100, T80, and T70 refer to the retention of 100%, 80%, and 70% of initial PCE, respectively. This work provides an effective strategy to advance the performance of NiO_x-based inverted PSCs.