A benzo[1,2-b:4,5-b′]difuran- and thieno-[3,4-b]thiophene-based low bandgap copolymer for photovoltaic applications

• DOI: 10.1039/c2py20580g
• Publication Date: 2012-09-12T15:06:26Z
• Authors: Bo Liu; Xuewen Chen; Yingping Zou; Yuehui He; Lu Xiao; Xinjun Xu; Lidong Li; Yongfang Li
• Keywords: 02 engineering and technology; 0210 nano-technology; 7. Clean energy; 01 natural sciences; 0104 chemical sciences

A new low bandgap conjugated polymer—PBDFTT-C was synthesized from thieno-[3,4-b]thiophene and benzo[1,2-b:4,5-b′]difuran units by Stille coupling reactions. The structure was verified by 1H NMR and elemental analysis, the molecular weight was determined by gel permeation chromatography (GPC) and the thermal properties were investigated by thermogravimetric analysis (TGA). PBDFTT-C showed a low HOMO energy level of −5.27 eV. The polymer film displayed broad absorption in the wavelength region from 300 nm to 840 nm with a low bandgap of 1.48 eV. The field effect hole mobility of PBDFTT-C reached 5.4 × 10−3 cm2 V−1 s−1. By using 1,8-diiodooctane (DIO) as the solvent additive, photovoltaic cells with the structure of ITO/PEDOT:PSS/PBDFTT-C:PC71BM (1 : 1.5, w/w)/Ca/Al demonstrated a power conversion efficiency of 4.4% with a short circuit current of 10.45 mA cm−2, open circuit voltage of 0.66 V and a fill factor of 0.64, under the illumination of AM 1.5G, 100 mW cm−2.