Spiro‐Linked Bisphosphonate Self‐Assembled Monolayers for Efficient and Stable Perovskite Solar Cells

Bisphosphonate‐anchored self‐assembled monolayers (SAMs) play a pivotal function in the development of high‐performance inverted perovskite solar cells (PSCs). However, the strong aggregation tendency of SAM molecules on substrates significantly limits the power conversion efficiency (PCE) of the devices. In this study, a spirocyclic linkage strategy is introduced for the first time into the molecular design of bisphosphonate‐based SAM hole‐transporting materials, and three target compounds, SCF‐4PADCB, SF‐4PADCB, and SFT‐4PADCB, are successfully synthesized. The twisted spiro‐conformation effectively suppresses intermolecular π–π stacking aggregation. In addition, SCF‐4PADCB hole‐transporting layer optimizes the interfacial energy level alignment, and passivates the defects of perovskite. Consequently, the inverted PSCs based on SCF‐4PADCB achieve a champion PCE of 26.58%. Moreover, the unencapsulated device retains 91.26% of its initial PCE after 1200 h of maximum power point tracking and exhibits outstanding ultraviolet stability. Impressively, SCF‐4PADCB also demonstrates excellent versatility, delivering a PCE of 23.46% in 1.68 eV wide‐bandgap PSCs and a superior indoor PCE of 43.65% under 1000 lux LED illumination. This work provides a promising molecular design strategy for developing novel SAMs toward highly efficient and stable PSCs.