Bidentate Hole-Transporting Materials for Interface Passivation and High-Efficiency Inverted Perovskite Solar Cells

Interface engineering using multifunctional materials is central to advancing both efficiency and operational stability in perovskite solar cells (PSCs). Here, we report a family of enol-centered small-molecule hole-transporting materials (HTMs) DKcH, DKPh, and DKTPA rationally designed to couple efficient hole extraction with intrinsic interfacial defect passivation. The cooperative C═O and ‒OH moieties act as bidentate coordination sites, enabling strong chemical interactions with undercoordinated species at the perovskite surface. Systematic modulation of the secondary side arm from cyclohexyl to phenyl and triphenylamine progressively increases molecular conjugation, strengthens π-π stacking, and improves film cohesion and thermal robustness, establishing clear structure-property-function relationships. Benefiting from optimized electronic structure and interfacial functionality, DKTPA delivers superior device performance, enabling inverted MAPb(I_0.9C_0.1)₃-based PSCs to achieve a high-power conversion efficiency of 22.74%. Notably, DKTPA-based devices retain 90.35% of their initial efficiency after 500 h of continuous one-sun illumination. This work introduces enol-centered HTMs as a versatile functional-materials platform and provides general molecular design principles for stable, dopant-free interfacial layers in high-performance perovskite photovoltaics.