Synergistic effect driven: Mixed self-assembled monolayer achieves simultaneous enhancement of efficiency and stability in perovskite solar cells

Self-assembled monolayers (SAMs) serve as essential interfacial modification materials and have been extensively employed in high-performance perovskite solar cells (PSCs) to enhance charge transport efficiency, reduce interfacial defect density, and improve overall device performance. Despite their advantages, SAMs still encounter notable challenges in further enhancing the efficiency and long-term stability of PSCs. This study systematically investigates [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz), [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz), and their mixed SAMs. The findings reveal that a strategic combination of these two SAMs can substantially enhance device performance while maintaining robust stability. Within the mixed SAMs, MeO-2PACz contributes to improved charge transport efficiency and enhances the crystalline quality of the thin film, whereas the hydrophobic nature of Me-4PACz significantly bolsters the environmental stability of the device. PSCs fabricated with the mixed SAMs demonstrate commendable efficiency and exceptional stability, with the optimal device achieving a photoelectric conversion efficiency (PCE) of 21.92 %. The device retains 90 % of its initial efficiency after 600 h of aging in a glovebox environment and maintains 85 % of its initial efficiency after 288 h of aging in a high-humidity atmospheric environment. This study demonstrates that mixed SAMs hold significant potential for achieving high-performance and high-stability PSCs.