Synthesis and Photovoltaic Properties of A Dithieno[6,5- b :10,11- b ′]-8H-Cyclopentyl[1,2-b:4,3- b ′]Diphenanthrene based Donor-Acceptor Alternating Copolymer

A novel fused nonacyclic monomer of dithieno[6,5-b:10,11- b ′]-8H-cyclopentyl[1,2-b:4,3- b ′] diphenanthrene ( DTCPDP ) was synthesized by combining the structural features of ladder-type and multiple fused multi-cyclic aromatics. DTCPDP has a single sp3 -hybridized carbon bridge between fused multi-cyclic aromatics. The copolymerization of DTCPDT with the electron accepting unit of 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole ( DTBT ) via Stille coupling afforded a novel donor-acceptor (D-A) alternating copolymer PDTCPDT-DTBT . The copolymer exhibited good chemical and thermal stabilities, with an optical band gap of 1.82 eV and a low-lying highest occupied molecular orbital (HOMO) energy level of -5.32 eV. When the copolymer was incorporated into polymer: fullerene (PC 71 BM) blends to fabricate bulk heterojunction polymer solar cell devices, the devices exhibited a moderate maximum power conversion efficiency (PCE) of 5.90%.