Regular Copolymer Acceptor with Enhanced Molecular Stacking Enables 20.03% Efficiency in Binary All-Polymer Solar Cells.

Abstract

Ternary random copolymerization, which enables precise control over optoelectronic characteristics and processing compatibility by incorporating a third functional unit, serves as an effective method for tailoring polymer acceptor properties. However, competing reactivity ratios of monomers during random copolymerization induce sequence inhomogeneity, disrupting the periodic arrangement of monomers and the structure of polymer acceptor molecules. The intricate intermolecular interactions and aggregation behaviors in random copolymers pose significant challenges for achieving optimal morphology. Herein, we propose the concept of ternary regular copolymerization, which precisely controls copolymer microstructure, aligns the monomer arrangement, and enhances crystallization. Regular copolymers (named RC10) and random copolymers (named UC10) were synthesized by using monomers containing benzothiadiazole and benzoquinoxaline units. The intramolecular alternating arrangement of monomers endows the polymer acceptor with a well-defined molecular conformation and enhanced molecular stacking. Consequently, the binary device based on PM6:RC10 achieves an impressive efficiency of 20.03%. Furthermore, another two regular copolymers were synthesized and characterized, both of which exhibit better photovoltaic performance as compared to that of their random counterparts, demonstrating the broad applicability of this strategy. Our study reveals that regular copolymerization holds significant potential for regulating molecular aggregation and alignment in polymer acceptors, providing valuable insights for designing high-performance acceptor materials.