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

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 pi-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 pi-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 pi-conjugated oligomers with varied numbers of repeating units.