Synthesis and photovoltaic performance of a low bandgap fluorinated phenanthrenequnioxaline-based conjugated polymer

A novel alternating copolymer with benzo[1,2-b:4,5-b′]dithiophene as electron-rich unit and fluorinated phenanthrenequinoxaline segment as electron-withdrawing unit was synthesized. The polymer showed a low-lying highest occupied molecular orbit energy level of −5.34 eV with a very low bandgap of 1.53 eV. Solar cell devices were fabricated by using the polymer as donor and [6,6]-phenyl-C71-butyric acid methyl ester as acceptor, respectively. The photovoltaic properties were studied and power conversion efficiency of 1.90% was obtained with an open-circuit voltage of 0.72 V for an optimal donor/acceptor weight ratio of 1:2 with 3% 1,8-diiodooctane. These results demonstrated that fluorine substituted phenanthrenequinoxaline based D–A conjugated polymer might be promising materials for bulk heterojunction photovoltaic cells.