Direct C–H Arylation-Derived Oligomeric Building Blocks Incorporated into Conjugated Polymers for Organic Solar Cell Applications

In this work, three conjugated oligomeric building blocks (BDD2, BDD3, and BDD4) containing respectively two, three, and four 1,3-bis(4-(2-ethylhexyl)thiophen-2-yl)-5,7-bis(2-alkyl)benzo1,2-c:4,5-c′dithiophene-4,8-dione (BDD) units with conjugation lengths that increase continuously were facilely produced in a single pot of direct C–H arylation (DACH). The integration of the above BDD derivatives with BDT produces three conjugated polymers with steadily elongated BDD units (i.e., PB(DB)2-T2F, PB(DB)3-T2F, and PB(DB)4-T2F) as a series of PBDB-T2F (also known as PM6) analogues. According to gel permeation chromatography analysis, a short conjugate length PB(DB)2-T2F with a high and homogeneous molecular weight is advantageous for charge transfer. By incorporating acceptor Y6 into bulk heterojunction (BHJ) system, the blend film was able to achieve excellent phase separation and a nanofiber structure, which in turn enhanced exciton dissociation and collection. As a result, the PB(DB)2-T2F:Y6 device was able to achieve a power conversion efficiency (PCE) of 10.84%. The incorporation of oligomeric monomers into polymers, developed in the current work, opens an avenue to access conjugated polymers and thus enriches the library of organic electronic materials.