Polymer Solar Cells Based on the Copolymers of Naphtho[1,2-c：5,6-c]bis（1,2,5-thiadiazole） and Alkoxylphenyl Substituted Benzodithiophene with High Open-Circuit Voltages

Two novel naphtho[1,2-c：5,6-c]bis（1,2,5-thiadiazole） and alkoxylphenyl substituted benzodithiophene based copolymers were developed as the donor materials for polymer solar cells. The resulting copolymers exhibit broad absorption bands in the range of 500--800 nm in thin films and deep highest occupied molecular orbital energy levels of-5.39 eV and -5.36 eV, respectively. The best device performance was achieved by PI, with an open-circuit voltage of 0.85 V, a short-circuit current density of 8.65 mA·cm^-2, a fill factor of 37.8%, and a power conversion efficiency of 2.78%.