Nonconjugated Self-Doped Polymer Zwitterions as Efficient Interlayers for High Performance Organic Solar Cells
Run Yang, Jing Tian, Wenxu Liu, YuXing Wang, Zhan Chen, Thomas P. Russell, Yao Liu
Abstract
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.