Molecular Synergy-Enabled Buried Interface Engineering Toward Highly Efficient and Operationally Stable Flexible Perovskite Photovoltaics.

Self-assembled monolayers (SAMs) have become pivotal hole-selective layers for efficient inverted perovskite solar cells (PSCs), yet conventional single-component SAMs suffer from severe intermolecular aggregation, insufficient thermal anchoring, and weak crystallization templating, which severely limit efficiency and operational stability, especially in flexible configurations. Herein, we demonstrate a rationally designed molecular engineering approach for constructing robust buried bottom interfaces via multifunctional SAMs featuring bidentate phosphonic acid anchors, electron-donating methoxy groups. Such elaborate molecular design enables strengthened interfacial binding, optimized energy-level alignment, suppressed self-aggregation, and oriented perovskite crystallization with relieved residual tensile strain. As a result, rigid PSCs achieve a champion efficiency of 27.15% (certified 26.51%), and flexible PSCs exhibit a remarkable efficiency of 25.37% with outstanding mechanical robustness. Moreover, the optimized devices deliver exceptional operational stability, retaining 97.5% of initial performance after 1000 h of continuous operation under ISOS-L-2 protocols. This work provides a universal molecular engineering paradigm toward high-performance and ultra-stable flexible perovskite photovoltaics via robust buried interface engineering.