Synthesis of Long‐Chain Oligomeric Donor and Acceptors via Direct Arylation for Organic Solar Cells†

Comprehensive Summary The rapid synthesis of structurally complicated electron donors & acceptors still remains a major challenge in organic solar cells (OSC). In this work, we developed a highly efficient strategy to access long‐chain oligomeric donor and acceptors for OSC applications. A series of cyclopentadithiophene (CPDT) and benzothiadiazole (BT)‐based π‐conjugated oligomers, i.e. , three oligomeric acceptors (BTDT) n ‐IC ( n = 1—3) and one long‐chain oligomeric donor (BTDT) 4 ‐RD, are facilely synthesized by an atom‐ and step‐economical, and labor‐saving direct C—H arylation (DACH) reaction ( i.e. , C—H/C—Br cross coupling). Note that (BTDT) 4 ‐RD involving five CPDT, four BT and two rhodamine (RD) building blocks is the longest oligomeric donor in the fullerene‐free OSC devices ever reported. The dependence of the structure‐property‐performance correlation of (BTDT) n ‐IC ( n = 1—3) and (BTDT) 4 ‐RD on the π‐conjugation lengths is thoroughly investigated by opto‐electrochemical measurements, bulk heterojunction (BHJ) OSC devices and microscopies. The (BTDT) 1 ‐IC:PBDB‐T and (BTDT) 4 ‐RD:Y6 BHJs achieve power conversion efficiencies of 9.14% and 4.51%, respectively. Our findings demonstrate that DACH reaction is a powerful tool to tune the opto‐electronic properties and device performances by regulating the lengths of π‐conjugated oligomers with varied numbers of repeating units.