Benzo[1,2-b:4,5-b′]difuran-Based Donor-Acceptor Copolymers for Polymer Solar Cells

Three new benzo[1,2-b:4,5-b']difuran-based donor-acceptor conjugated polymers, namely poly{4,8-bis(2'-ethylhexyloxy)benzo[1,2-b;3,4-b']difuran-alt-5,5-(4',7'-di-2-thienyl-5',6'-dioctyloxy-2',1',3'-benzothiadiazole)}(PBDFDODTBT), poly{4,8-bis(2'-ethylhexyloxy)benzo[1,2-b;3,4-b']difuran-alt-5,5-(4',7'-di-2-thienyl-2-octyl-2',1',3'-benzotriazole)}(PBDFDTBTz), poly{4,8-bis(2'- ethylhexyloxy)benzo[1,2-b;3,4-b']difuran-alt-5,5-(4',7'-di-2-thienyl-5',6'-dioctyloxy-benzo[c][1,2,5]oxadiazole)}(PBDFDTBO), were synthesized by Stille coupling polymerization reactions. All of the polymers were found to be soluble in common organic solvents such as chloroform, tetrahydrofuran and chlorobenzene with excellent film forming properties. Their structures were verified by H-1 NMR and elemental analysis, the molecular weights were determined by gel permeation chromatography (GPC) and the thermal properties were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The polymer films exhibited broad absorption bands. The hole mobility of PBDFDODTBT:PC71BM (1:2, w/w) blend reached up to 6.7 x 10(-2) cm(2).V-1.s(-1) by the space-charge-limited current (SCLC) method. Preliminary photovoltaic cells based on the device structure of ITO/PEDOT:PSS/PBDFDODTBT:PC71BM(1:2, w/w)/Ca/Al showed an open-circuit voltage of 0.69 V, a power conversion efficiency of 4.5% and a short circuit current of 9.87 mA.cm(-2).