Design and synthesis of the polymers based on alkylthiophenyl side chains and variant acceptor moieties for polymer solar cells

Abstract

Three donor–acceptor (D–A) copolymers PSB-DFBT, PSB-DTDFBT and PSB-FTT, consisting of alkylthiophenyl group-substituted benzo[1,2-b:4,5-b′]dithiophene (SB) as the donor moieties and different electron-deficient units as the acceptor moieties, have been designed and synthesized. The effects of the variant acceptor moieties on the photophysical, electrochemical and photovoltaic properties of the polymers were investigated. Compared with the polymers PSB-DFBT and PSB-DTDFBT with 5,6-difluorobenzo[c][1,2,5]thiadiazole as the acceptor moieties, the polymer PSB-FTT with 2-ethylhexyl-3-fluorothieno[3,4-b]thiophene-2-carboxylate (FTT) as the acceptor moieties shows smaller band gap, stronger light harvesting capacity, better appropriate microphase separation with (7,7)-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM), smaller domain size, more effective exciton dissociation and higher hole mobility. Therefore, the PSB-FTT-based bulk heterojunction solar cell exhibits a higher power conversion efficiency of 4.45% than that of the PSB-DFBT- (1.88%) and PSB-DTDFBT-based devices (0.48%).