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 (<1.5% PCE variation across molecular weights of 6.9-33.8 kDa), outstanding thickness tolerance (retaining 80% PCE at 133 nm), and scalability (17.26% PCE for a 1.05 cm² device and 15.12% PCE for a 13.5 cm² module). This facile approach for designing high-performance thickness-insensitive CIMs paves the way for the industrial-scale production of efficient OSCs.