Dense and Uniform Co-Self-Assembled Monolayers for Modifying NiOX toward High-Performance Perovskite Solar Cells

Self-assembled molecules (SAMs) have emerged as an efficient strategy for addressing buried nickel oxide (NiOX) interface defects in inverted perovskite solar cells (PSCs). Nevertheless, conventional carbazole-based SAMs suffer from weak intermolecular interactions, leading to film aggregation that hinders the formation of dense and uniform SAMs, which in turn causes discontinuities in the contact between NiOX and the perovskite film, thereby inducing interfacial defects and nonradiative recombination. Herein, 1-(2-carboxyethyl)-2,3,3-trimethyl-3H-indol-1-ium (CTI) was combined with 2PACz to prepare co-SAMs for modifying the NiOX substrate. Benefiting from the complementary charge distribution of the conjugated moieties in CTI and (2-(9H-carbazol-9-yl)ethyl)phosphonic acid (2PACz), the intermolecular π–π stacking interactions are significantly strengthened, thereby enabling the preparation of uniform and dense co-SAMs. The resulting embedded interface is in close contact with the perovskite film, which substantially elevates the crystallinity of the perovskite film and reduces defect density. Consequently, inverted devices based on the optimized 2PACz+CTI not only achieved an impressive photoconversion efficiency of 25.12% but also demonstrated excellent long-term storage stability under high-temperature and humid conditions.