A simple route to linear and hyperbranched polythiophenes containing diketopyrrolopyrrole linking groups with improved conversion efficiency

Abstract

Two novel polythiophene derivatives with linear or hyperbranched architectures using diketopyrrolopyrrole (DPP) as linking groups as well as normal poly(3-hexylthiophene) (P3HT) were synthesized via the Universal Grignard metathesis polymerization. The molecular weights of the linear polythiophene containing DPP linking moieties are higher than those of P3HT, while molecular weights of the hyperbranched one are smaller. The main decomposition temperatures of polymers were measured at 470 °C from TGA experiments. The UV-vis absorption behaviors of the DPP-containing polymers are similar to that of P3HT; moreover, these DPP-containing polythiophenes show distinct PL decay both in solution and thin film states. The electrochemical experiments reveal that the incorporation of DPP groups resulted in lowering HOMO levels of polymers. All polymers were blended with PC61BM and used as active layers for the fabrication of inverted polymer solar cells. The power conversion efficiency of devices based on linear and hyperbranched polythiophenes reached 3.74% and 2.38%, respectively, revealing comparable or even higher efficiency than the one based on normal P3HT.