New narrow-band-gap conjugated copolymers based on benzodithiophene: Synthesis and photovoltaic properties

Four new alternating narrow-band-gap copolymers based on benzodithiophene are synthesized under conditions of the Stille reaction. In comparison to benzodithiophene homopolymers, all these copolymers show good solubility in common organic solvents and broad absorption in the visible spectrum of sunlight. The band gaps of the polymer films, as estimated from the cyclic voltammetry data, vary within 1.34–2.28 eV, and the position of the highest occupied molecular orbital lies in the range 4.99–5.72 eV. The values of the open-circuit voltage and the efficiency of polymer solar cells based on the copolymers are within 0.22–0.65 V and 0.02–0.48%, respectively.