Synthesis and photovoltaic performance of a series of small band gap polymers

A series of four small band gap polymers have been synthesized and have been incorporated into bulk heterojunction solar cells. The polymers were prepared via Yamamoto coupling and consist of alternating electron-rich dithiophene and electron-deficient bisquinoxaline or thienopyrazine units. In the thin solid films the optical band gaps (Eg) vary from 1.38 eV for the bisquinoxaline to 1.21 eV for thienopyrazine containing polymers. All polymers provide a photovoltaic response when blended with a methanofullerene as electron acceptor in the near infrared region up to the optical band gap. The best cells reach an efficiency of η = 1.5% under estimated standard solar light conditions (AM1.5G, 100 mW/cm2).