Dual-Site Coordination of a Novel Triphenylamine-Based Self-Assembled Monolayer for Efficient and Stable Inverted Perovskite Solar Cells

Precise regulation of interfacial charge transport dynamics and perovskite crystallization kinetics is critical for fabricating high-performance inverted (p-i-n) perovskite solar cells (PSCs). In this work, we engineered a novel self-assembled monolayer (SAM), SPA, featuring an electron-donating triphenylamine (TPA) core integrated with cyano and peripheral methylthio (-SCH₃) functional groups. Unlike the conventional Me-4PACz, SPA establishes a robust dual-site coordination with undercoordinated Pb²⁺ ions, as evidenced by significant red-shifts in FTIR stretching vibrations and binding energy shifts in XPS. This dual-functional interaction not only effectively passivates buried traps but also dictates crystallization kinetics, yielding high-quality perovskite films with monolithic grains and a highly preferred [h00] orientation. Consequently, SPA-based inverted PSCs achieve a champion power conversion efficiency (PCE) of 26.13% alongside a remarkable fill factor of 85.87%. Furthermore, this robust chemical anchoring translates into exceptional operational stability; unencapsulated devices maintained over 80% of their initial PCE for ∼460 h under continuous AM 1.5G illumination at ∼65 °C under open-circuit conditions.