Synthesis and photovoltaic properties of a donor-acceptor double-cable polythiophene with high content of C60 pendant

A new soluble donor-acceptor (D-A) double-cable polythiophene with higher content of C-60 pendant, PT-F, was synthesized. The photophysical, electrochemical, and photovoltaic properties of PT-F were investigated and compared with its control polymer PT-K without C-60 on its side chain. The polymer PT-F exhibited the characteristic reduction peaks of C-60 at -0.783, -1.187, and -1.651 V vs Ag/Ag+, which indicates that the electronic properties of C-60 remained in the double-cable polymer. In comparison with PT-K, the onset oxidation potential of PT-F was increased from 0.2 to 0.3 V vs Ag/Ag+, which could be ascribed to the steric hindrance of the big fullerene side chain. The results of the absorption and photoluminescent spectra indicate that there is no interaction at ground state between polythiophene main chains and C-60 on the side chains, but there is strong interaction between them at excited state. The maximum power conversion efficiency of the polymer solar cell based on PT-F reached 0.52% under AM 1.5, 100 mW/cm(2), which is 5 times higher in comparison with that (0.10%) of the device based on PT-K blended with 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-C-61 under the same experimental conditions. The efficiency of 0.52% is the highest value for the PSCs based on the double-cable polymers reported in the literature until now.