Structural variation of donor–acceptor copolymers containing benzodithiophene with bithienyl substituents to achieve high open circuit voltage in bulk heterojunction solar cells

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2013-01, Vol.1 (48), p.15535-15543
• Main Authors: Kularatne, Ruvini S., Taenzler, Ferdinand J., Magurudeniya, Harsha D., Du, Jia, Murphy, John W., Sheina, Elena E., Gnade, Bruce E., Biewer, Michael C., Stefan, Mihaela C.
• Format: Article
• Language: English
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c3ta13686h

Three new donor-acceptor copolymers P1, P2, and P3 were synthesized with benzodithiophene with bithienyl substituents as the donor and 5,6-difluorobenzo[c][1,2,5]thiadiazole, 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole, and 5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]t hiadiazole as the acceptors, respectively. The insertion of thiophene spacer between the donor and the acceptor broadened the absorption of the polymers P2 and P3 and resulted in a red shift of similar to 30 nm as compared to that of the polymer P1. However, the inclusion of fluorine atoms on the polymer had detrimental effects on the photovoltaic properties of the polymers. The synthesized donor-acceptor polymers were tested in bulk heterojunction (BHJ) solar cells with [6,6]-phenyl C sub(71) butyric acid methyl ester (PC sub(71)BM) acceptor. Polymer P2 gave a PCE of 3.52% with PC sub(71)BM in which the active layer was prepared in chloroform with 3% v/v 1,8-diiodooctane (DIO) additive. The effect of fluorine substitution and thiophene group insertion on the UV/Vis absorbance, photovoltaic performances, morphology, and charge carrier mobilities for the polymers are discussed.