Synthesis and Photovoltaic Properties of Thieno[3,2-b]Thiophene-Incorporated Quinoxaline-Based Conjugated Donor Polymers

Abstract

Novel electron-donor and electron-acceptor type copolymers based on 2,3-bis(thieno(3,2-b)thiophen-2-yl)-5,8-di(thiophen-2-yl)quinoxaline, PBT-TTDTQx and PTT-TTDTQx, were synthesized as active materials for organic photovoltaic cells. 2,2'-Bithiophene (BT) and thieno[3,2-b]thiophene (TT) moieties were introduced as co-monomers during polymerization in order to compare optical, electrochemical, charge transport, and photovoltaic properties. The synthesized polymers possessed low bandgaps (similar to 1.65 eV) suitable for efficient solar absorption and good solubility organic solvents such as chloroform, chlorobenzene, and o-dichlorobenzene. Bulk heterojunction (BHJ) photovoltaic cells with the structure of indium tin oxide (ITO)/ZnO/Polymer[6,6]-phenyl-C(71)butyric acid methyl ester (PC71BM)/MoO3/Ag were fabricated. The power conversion efficiency (PCE) of PTT-TTDTQx containing TT moiety (2.15%) was much higher than that of PBT-TTDTQx having BT unit (1.02%), under AM 1.5G (100 mW/cm(2)) illumination, owing to the rigid planar structure of TT as well as its strong electron-donating properties.