Polymerization of tellurophene derivatives by microwave-assisted palladium-catalyzed ipso-arylative polymerization

We report the synthesis of a tellurophene-containing low-bandgap polymer, PDPPTe2T, by microwave-assisted palladium-catalyzed ipso-arylative polymerization of 2,5-bis[(α-hydroxy-α,α-diphenyl)methyl]tellurophene with a diketopyrrolopyrrole (DPP) monomer. Compared with the corresponding thiophene analog, PDPPTe2T absorbs light of longer wavelengths and has a smaller bandgap. Bulk heterojunction solar cells prepared from PDPPTe2T and PC71 BM show PCE values of up to 4.4%. External quantum efficiency measurements show that PDPPTe2T produces photocurrent at wavelengths up to 1 µm. DFT calculations suggest that the atomic substitution from sulfur to tellurium increases electronic coupling to decrease the length of the carbon-carbon bonds between the tellurophene and thiophene rings, which results in the red-shift in absorption upon substitution of tellurium for sulfur.