Mixed Self-Assembled Hole-Transport Monolayer Enables Simultaneous Improvement of Efficiency and Stability of Perovskite Solar Cells

As one of the interface engineering methods for realizing high-performance perovskite solar cells (PSCs), self-assembled monolayers (SAMs) with hole-transport properties have recently been applied as an effective way to reduce energy losses at the hole-transport layer/perovskite interface, especially in PSCs with p-i-n structure. However, there are still limitations in implementing PSC with high efficiency and high stability due to the inherent weaknesses of single SAMs. Herein, it is demonstrated that a mixed self-assembled hole-transport monolayer with an appropriate mixture of [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz) and [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) enables simultaneous improvement of efficiency and stability of PSCs. In the mixed SAM, MeO-2PACz maintains favorable wettability to produce high-quality films, while the deep highest occupied molecular orbital of Me-4PACz optimizes the energy level for efficient charge transfer, resulting in improved PSC performance. Encouragingly, Me-4PACz mitigates the stability issues of MeO-2PACz, producing mixed SAM-based PSCs with excellent stability. These PSCs achieve up to 20.63% efficiency and exhibit excellent thermal long-term stability, retaining 90% and 80% of their initial efficiency after approximately 1400 and 2100 h at 65 degrees C in an N2 atmosphere. These findings suggest the potential of mixed SAM approaches for the realization of high-performance PSCs. Herein, the effect of mixed self-assembled hole-transport monolayers, which blend [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid and [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid, on the efficiency and stability of perovskite solar cells (PSCs) is investigated. It is found that mixed self-assembled monolayer (SAM) enables simultaneous improvement of efficiency and stability of PSCs. These findings suggest the potential of mixed SAM approaches for the realization of high-performance PSCs.image (c) 2024 WILEY-VCH GmbH