Side-chain manipulation on accepting units of two-dimensional benzo[1,2-b:4,5-b′]dithiophene polymers for organic photovoltaics

Abstract

Two donor–acceptor alternating polymers of bis(octylthio)thienyl benzo[1,2-b:4,5-b′]dithiophene (BDTTs) and fluorinated benzo[c][1,2,5]thiadiazole (fBT) or 5-dodecylthienyl-6-fluorobenzo[c][1,2,5]thiadiazole were designed for organic photovoltaic applications. The polymers displayed strong absorptions in the range of 300–650 nm and bandgaps of ∼1.60 eV. Bulk-heterojunction solar cells of PBDTTs-fBT and (6,6)-phenyl C₇₁-butyric acid methyl ester (PC₇₁BM) blends exhibited a maximum power conversion efficiency of 6.27%. Experimental results and theoretical modelling were correlated to reveal the impact of substitution on fluorinated BT on the optoelectronic properties of the resulting polymers.