Synthesis and characterization of alternating and random conjugated polymers derived from dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene and 2,1,3-benzothiadiazole derivatives

Abstract

Alternating and random low band gap conjugated copolymers with dialkyloxy flanked-dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene derivatives (DTBDTs) as electron donor moieties and 5,6-di(dodecyloxy)-2,1,3-benzothiadiazole (BT) as electron acceptor moieties were synthesized and characterized. Both of the conjugated polymers exhibited extensive light absorption ability from approximately 330 to 680 nm with an optical band gap of approximately 1.82–1.87 eV. Unfortunately, the photovoltaic performance of the device derived from the alternating copolymer was limited by its poor solubility and low molecular weight. Compared with the alternating copolymer, the solubility, molecular weight and photovoltaic performance of the random copolymer were better, and maximal power conversion efficiencies (PCEs) of 3.15% and 4.73% were achieved in the photovoltaic cells (PVCs) with the random conjugated polymer as electron donor materials and [6,6]-phenyl-C71 butyric acid methyl ester (PC71BM) or indene-C60 bisadduct (IC60BA), respectively, as electron acceptor materials under 100 mW cm−2 illumination (AM 1.5G). The alternating and random low band gap conjugated copolymers with dialkyloxy flanked-dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene derivatives (DTBDTs) as electron donor moieties and 5,6-di(dodecyloxy)-2,1,3-benzothiadiazole (BT) were first synthesized and characterized. As compared with the alternating copolymers, the solubility and molecular weight of the random copolymer was clearly increased. Power conversion efficiencies (PCEs) of 2.41, 3.15 and 4.73% have been achieved in the photovoltaic cells (PVCs) from the random copolymer.