Design and photovoltaic properties of conjugated polymers based on quinoxaline and diketopyrrolopyrrole for OSCs

Abstract

We report the synthesis of low bandgap polymers containing a difluoroquinoxaline unit by Stille polymerization for use in organic solar cells (OSCs). A new series of copolymers were synthesized with 2, 3-didodecyl-6, 7-difluoro-quinoxaline and pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione as electron-deficient units and thiophene or bithiophene as the electron-rich unit. The bithiophene moiety in one of the polymers was associated with reduced electron density because of a weak push-pull effect and an increase in the highest occupied molecular orbital (HOMO) energy level. Efficient polymer solar cells were fabricated by blending the synthesized copolymers with the fullerene PC71BM, and the PCE was measured to be 3.41% under 100 mW/cm(2) AM 1.5 G illumination. These results demonstrate that the careful design of a balanced chemical structure is crucial for high performance polymer solar cells.