Polymer Solar Cells Based on Alternating and Statistical 4,7-Bis(4-octylphenyl-2-thienyl)-2,1,3-benzothiadiazole Copolymers

A series of copolymers based on variable contents of 4,7-bis(4-octylphenyl-2-thienyl)-2,1,3-benzothiadiazole (1) and dioctylfluorene were synthesized by Suzuki, Yamamoto and oxidative coupling methods. The octylphenyl substituent introduced on 1 confers high solubility and enables high-molecular-weight polymers to be synthesized. Using the different methods of polymerization, the content of 1 may be tuned to cover the range of absorption profiles over the visible spectrum, and the sequence distribution can be varied from alternating to statistical. Suzuki coupling provided copolymers in which 1 is flanked by dioctylfluorene units and that exhibited a high quantum yield of photoluminescence. A corresponding alternating polymer, poly[dioctylfluorene-alt-4,7-bis(4-octylphenyl-2-thienyl)-2,1,3-benzothiadiazole], prepared by Suzuki coupling, exhibits a higher photoluminescent quantum efficiency of 0.54 in the solid state and small red-shifts of its absorption and emission spectra from solution to solid, indica...