Drastic Changes in Properties of Donor–Acceptor Polymers Induced by Asymmetric Structural Isomers for Application to Polymer Solar Cells

Appropriate design of donor–acceptor (D-A) conjugated polymers is important for enhancing their physical, optical, and electrochemical properties. The rapid development of D-A conjugated polymers based on fullerene and nonfullerene derivatives in the past decade has led to an improvement in the performance of polymer solar cells (PSCs). In this study, we designed and synthesized two donor polymers based on the DTffBT acceptor unit, with matching optical absorption range and energy levels with fullerene (PC71BM) and nonfullerene acceptors (ITIC and IDIC), by introducing asymmetric structural isomers of donor units. We demonstrated that materials design by structural modification dramatically affects the physical, optical, and electrochemical properties as well as the crystallinity and photovoltaic performance of the polymers. The results provide valuable insights into materials design for efficient PSCs.