Synthesis of Poly(4,4-dialkyl-cyclopenta[2,1-b:3,4-b′]dithiophene-alt-2,1,3-benzothiadiazole) (PCPDTBT) in a Direct Arylation Scheme

Poly(4,4-dialkyl-cyclopenta[2,1-b:3,4-b']-dithiophene-alt-2,1,3-benzothiadiazole) (PCPDTBT), a potentially interesting low bandgap donor copolymer for bulk heterojunction-type organic solar cells with a power conversion efficiency >5.5%, can be now synthesized in a direct arylation scheme starting from 4,4-dialkyl-cydopenta-[2,1-b:3,4-b']dithiophene (CPDT) and 4,7-dibromo-2,1,3-benzothiadiazole (4,7-dibromo-BT) as monomers. The direct arylation procedure leads to PCPDTBT with an M-n of up to 40 000 and circumvents the use of costly diboronic acid/ester or distannyl monomers.