Donor–Acceptor Polymers Containing 4,8-Dithienylbenzo[1,2-b:4,5-b′]dithiophene via Highly Selective Direct Arylation Polymerization

While palladium-catalyzed direct arylation polymerization (DArP) is an easy and safe method to synthesize semiconducting polymers with alternating donor–acceptor units (DA polymers), branching and cross-linking defects arising from unintended side reactions are common. When these polymers are used as electronic materials in organic solar cells (OSCs) and similar devices, these defects may adversely affect device performance. We have recently shown that the side reactions can be inhibited by the simultaneous presence of two ligands, P(2-MeOC6H4)3 and N,N,N′,N′-tetramethylethylenediamine (TMEDA). In this study, an efficient donor polymer for OSCs (P1), based on 4,8-dithienylbenzo[1,2-b:4,5-b′]dithiophene (DTBDT) units, was prepared with this mixed-ligand method. The DA polymer is found to exhibit a well-controlled structure, with homocoupling defects of 2.0%, compared to 14.8% observed in the Migita–Stille product (P2). The power conversion efficiency (PCE) was 9.9% when P1 was used, compared to 9.8% for P2 in bulk-heterojunction-type OSC with a nonfullerene acceptor. This demonstrates the effectiveness of the DArP method as a clean and safe alternative method to synthesize DTBDT-based DA polymers for OSCs.