Synthesis and photovoltaic properties of two new alkoxylphenyl substituted thieno[2,3-f]benzofuran based polymers

Two new alkoxylphenyl substituted thieno[2,3-f]benzofuran (TBFP)-based polymers (PTBFP–BT and PTBFP–BO) were designed and synthesized. Their structures were verified by nuclear magnetic resonance (NMR) spectroscopy, the molecular weights were determined by gel permeation chromatography (GPC) and the thermal properties were investigated by thermogravimetric analysis (TGA). The two polymers showed similar UV-Vis absorption spectra with a broad and strong absorption band from 300–750 nm in solid state. The resulting copolymers exhibited relatively deep highest occupied molecular orbital (HOMO) energy levels (−5.47 and −5.61 eV) for PTBFP–BT and PTBFP–BO, respectively. The device fabricated with PTBFP–BT : PC71BM (1 : 2) showed better balanced hole and electron mobility of 2.49 × 10−4 cm2 V−1 s−1 and 9.12 × 10−4 cm2 V−1 s−1, respectively, than those of PTBFP–BO based devices. The polymer solar cells (PSCs), based on the single layer device structure of ITO/PEDOT:PSS/PTBFP–BT : PC71BM (1 : 2, w/w)/ZrAcac/Al with 3 vol% 1,8-diiodooctane (DIO) as additive, showed a relatively high power conversion efficiency (PCE) of 6% under the illumination of AM 1.5G, 100 mW cm−2, with a high fill factor (FF) of 0.69.