Enhanced photocurrent generation by high molecular weight random copolymer consisting of benzothiadiazole and quinoxaline as donor materials

Abstract

We synthesized organic photovoltaic materials that have high molecular weight and good solubility. A new random copolymer named poly[carbazole-co-dithienylbenzothiadiazole-co-dithienylquinoxaline] (PC-TBT-TQ) was polymerized through the Suzuki coupling reaction. PC-TBT-TQ was dissolved in a common organic solvent, and its Mn indicates a high molecular weight of 216.2kg/mol. According to the result of thermal analysis, very high thermal stability was observed, with an approximately 5wt% weight loss at 440°C. The optical band gap of PC-TBT-TQ (1.89eV) is slightly higher than that of PCDTBT (1.87eV). The HOMO and LUMO levels of PC-TBT-TQ (HOMO level: 5.45eV, LUMO level: 3.56eV) are similar to those of PCDTBT (HOMO level: 5.45eV, LUMO level: 3.58eV). The OPV properties of the polymer were assessed by fabricating bulk-heterojunction polymer solar cells in the ITO/PEDOT:PSS/active-layer/BaF2/Ba/Al structure. When PC-TBT-TQ and PC71BM were fabricated in a 1:4 ratio, the open-circuit voltage (VOC), short-circuit current (JSC), fill factor (FF) and power conversion efficiency (PCE) were 0.83V, 9.5mA/cm2, 43.3% and 3.5%, respectively.