Low bandgap polymers with benzodithiophene and bisthienylacrylonitrile units for photovoltaic applications

Novel copolymers (P1 and P2) comprising (E)-2,3-bis(2-thienyl)acrylonitrile and benzo[1,2-b;4,5-b′]dithiophene derivatives are designed and synthesized to be applied as an electron donor material in polymer solar cells blended with PC61BM as an electron acceptor. These copolymers show a good thermal stability with a 5% weight loss temperature beyond 340 °C, and their films exhibit a broad absorption band with a low optical bandgap of ca. 1.84 eV. Polymer solar cells based on P2, prepared under optimized preparation conditions, are found to exhibit a short-circuit photocurrent of 10.71 mA cm−2, an open-circuit photovoltage of 600 mV, a fill factor of 65%, and a power conversion efficiency of 4.17% under AM 1.5 illumination conditions, 100 mW cm−2.