Synergistic Engineering of Substituents and Backbones on Donor Polymers: Toward Terpolymer Design of High-Performance Polymer Solar Cells

Design of terpolymers via copolymerization has emerged as a potential strategy for expanding the family of high-performing donor polymers and boosting the photovoltaic performance of non-fullerene polymer solar cells (PSCs). Herein, double-ester-substituted thiophenes and thienothiophenes are incorporated as third building blocks into the donor polymer PBDB-TF, developing two groups of terpolymers with donor-acceptor 1-donor-acceptor 2 (D-A1-D-A2)-type backbones. An optimum 10% concentration of double-ester-substituted thiophene units in PBDB-TF-T10 downshifts the molecular energy and increases the dielectric constant, and delivers proper miscibility and nanostructure in blends with the high-performing acceptor Y6. These characteristics are designed to synergistically enhance the photovoltage, photocurrent, and efficiency of PSCs. The resulting power conversion efficiency (PCE) of 16.4% surpasses the conventional PBDB-TF/Y6 PSCs, and it is among the best-performing PSCs based on PBDB-TF-derived terpolymers. Gratifyingly, PBDB-TF-T10 does not show significant batch-to-batch variation and it retains high PCEs above 16% in a broad range of molecular weights. This work introduces a facile strategy to easily synthesize terpolymers in combination with Y6 for the attainment of high-performing and reproducible non-fullerene PSCs.