Synthesis and photovoltaic properties of dithieno[3,2-b:2′,3′-d]silole-based conjugated copolymers

Abstract

A new low band gap conjugated polymer containing a dithieno[3,2-b:2′,3′-d]silole (DTS) donor unit and a fluorinated 4,7-dithien-2-yl-2,1,3-benzothiadiazole (DTffBT) acceptor unit was synthesized by Stille cross-coupling polymerization. The structural and thermal properties of the copolymer were characterized by using nuclear magnetic resonance, gel permeation chromatography and thermogravimetric analysis. This copolymer shows good thermal stability with a decomposition temperature of 325 °C and a broad absorption band from 300 to 800 nm. The HOMO and LUMO energy levels were estimated to be −5.28 and −3.66 eV, with an electrochemical band gap of 1.62 eV. Efficient bulk heterojunction solar cells were fabricated by blending this copolymer with PC₇₁BM, and they reached a power conversion efficiency up to 5.26% under 100 mW cm⁻² AM 1.5 illumination, indicating that PDTS–DTffBT is a potential candidate for polymer solar cells.