Nonconjugated Self-Doped Polymer Zwitterions as Efficient Interlayers for High Performance Organic Solar Cells

Polymer zwitterions are more promising cathode interlayers (CILs) for fused-ring electron acceptor (FREA)-based organic solar cells (OSCs) than amine-containing CILs and polyelectrolytes. However, they usually suffer from high synthetic cost and low electron mobilities. Herein, we present a novel strategy that combines the n-type doping effect with polymer zwitterions to develop a new nonconjugated self-doped polymer zwitterion (s-PZ), namely, PDI- M -DAN. PDI- M -DAN is afforded via cost-effective transition-metal-free polymerization and exhibits 200-fold higher electron mobility than the nondoped reference, thus making it an efficient and thickness-insensitive CIL for FREA-based OSCs. Power conversion efficiencies (PCEs) over 17% for interlayer thicknesses ranging from 12 to 30 nm with a maximum PCE of 17.82% are realized in D18:Y6-based OSCs. An impressive PCE and fill factor (FF) of 17.56 and 78.03% are also realized in PM6:Y6-based OSCs; both values are among the best ones in PM6:Y6-based binary OSCs. The effectiveness of our strategy in generating efficient CILs is evidenced by two other s-PZs, namely, PDI- N -DAN and NDI- M -DAN. Using PDI- N -DAN and NDI- M -DAN as the CILs, we obtained PCE values of 18.17 and 17.60% in D18:Y6-based OSCs, respectively. The PCE of 18.17% is among the highest for single-junction binary OSCs.