Thickness-Insensitive Cathode Interlayer via Molecular-Scale Distance Regulation for Efficient Organic Solar Cells

Cathode interlayers (CILs) are critical for optimizing the performance of organic solar cells (OSCs). However, the development of thickness-insensitive cathode interlayer materials (CIMs) suitable for large-scale printing remains an urgent yet underexplored challenge. In this work, we present a molecular-scale distance regulation strategy to design efficient CIMs by precisely tuning the flexible conjugation-break spacer lengths between n-type organic semiconducting units. Using this approach, we synthesized three CIMs (P3, P6, and P9) with trimethylene, hexamethylene, and nonamethylene spacers linking the 4,5,9,10-pyrene diimide (PyDI) acceptor units. Among them, P6 demonstrates optimal π–π stacking, efficient Br – doping, and enhanced conductivity, leading to improved charge collection and exciton utilization. As a result, P6-based binary and ternary OSCs achieved remarkably high power conversion efficiencies (PCEs) of 19.90 and 20.04%, respectively. Importantly, P6 exhibits excellent batch-to-batch consistency (