Ruvini S. Kularatne

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

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]thiadiazole 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 ∼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 C71 butyric acid methyl ester (PC71BM) acceptor. Polymer P2 gave a PCE of 3.52% with PC71BM 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.

Benzodithiophene homopolymers synthesized by Grignard metathesis (GRIM) and Stille coupling polymerizations

Poly{4,8-bis(95-dodecylthiophene-2-yl)benzo[1,2-b:4,5-b′]dithiophene} has been synthesized by both Grignard metathesis (P1) and Stille coupling polymerizations (P2). Polymers P1 and P2 were characterized and their optoelectronic properties, charge carrier mobilities, and photovoltaic properties were compared. The field-effect mobilities of the polymers were measured on both untreated and heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane (FS) treated organic field effect transistor (OFET) devices. The polymers were also evaluated in bulk heterojunction (BHJ) solar cells with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the acceptor.