Random Polymer Donor for High-Performance Polymer Solar Cells with Efficiency over 14%

Constructing random copolymers has been regarded as an easy and effective approach to design polymer donors for state-of-the-art polymer solar cells (PSCs). In this work, we develop a naphtho[2,3-c]thiophene-4,9-dione-based copolymer PBN-Cl as a donor material for PSCs, and a moderate power conversion efficiency (PCE) of 11.21% is achieved with a relatively low fill factor (FF) of 0.615. We then incorporate a similar acceptor unit benzo[1,2-c:4,5-c′]dithiophene-4,8-dione (BDD) into the polymeric backbone of PBN-Cl to tune its photovoltaic performance, and a significantly higher PCE of 14.05% is achieved from the random polymer PBN-Cl-B80 containing 80% BDD unit. The enhanced PCE of the PBN-Cl-B80-based device mainly relies on the higher FF value, resulting from the improved charge mobility properties, reduced bimolecular and trap-assisted recombination, and more appropriate phase separation. The results demonstrate a feasible strategy to tune the photovoltaic performance of polymer donors by constructing a random polymer with a compatible component.