A new benzo[1,2-b:4,5-b′]difuran-based copolymer for efficient polymer solar cells

Abstract

A new donor–acceptor type copolymer, namely poly{4,8-bis(2-ethylhexyloxy)benzo[1,2-b:3,4-b′]difuran-alt-6-octylnaphtho[2,3-c]thiophene-4,9-dione} (PBDFNTDO) was synthesized by a Stille coupling reaction and characterized by 1H NMR, GPC, TGA, UV-Vis absorption spectroscopy and cyclic voltammetry. PBDFNTDO is readily soluble in common organic solvents with a number-average molecular weight (Mn) of 10.7 kDa mol−1 and a polydispersity index of 1.71. TGA analysis shows the copolymer exhibits good thermal stability with 5% weight loss at a temperature of 341 °C. PBDFNTDO possesses a broad absorption band at 300–750 nm with an optical bandgap of 1.65 eV. Cyclic voltammetry gives HOMO and LUMO energy levels of −5.33 eV and −3.40 eV, respectively. The hole mobility of PBDFNTDO:PC71BM (1 : 1.5, w/w) reaches up to 5.0 × 10−3 cm2 V−1 s−1 by the space-charge-limited current (SCLC) method. A polymer solar cell with the configuration of ITO/PEDOT:PSS/PBDFNTDO:PC71BM (1 : 1.5, w/w)/Ca/Al demonstrates a promising power conversion efficiency of 4.71% under the illumination of AM 1.5 G, 100 mW cm−2.