Synthesis and Photovoltaic Properties of a New Class of Donor-Acceptor Alternating Copolymers Containing Pechmann-Dye Derivatives

Over the last decade, various low bandgap copolymers that exhibit over 5{\%} power conversion efficiency have been developed. However, the synthesis of most low-bandgap polymers is complicated with relatively long synthetic routes and low yield. In this work, a new series of novel alternating copolymers composed of thiophene and Pechmann-dye derivatives were synthesized and used as an electron donor material of bulk heterojunction polymer solar cells. Two Pechmann-dye derivatives, 5,5'-bis-(3-octyl-thiophen-2-yl)-[3,3']bifuranylidene-2,2'-dione and 3,7-bis-(3-octyl-thiophen-2-yl)-pyrano[4,3-c]pyran-1,5-dione which have high molar absorption coefficient, strong electron-deficient core, and planar structure, were easily synthesized via simple three steps with high yield. The use of the Pechmann-dye derivatives as a building block for copolymers results in promising optical, electrochemical, and photophysical properties. Morphology, charge transport, and photovoltaic characteristics of the new copolymers will be discussed.