Synergistically Improved Molecular Doping and Carrier Mobility by Copolymerization of Donor-Acceptor and Donor-Donor Building Blocks for Thermoelectric Application

In this work, it is demonstrated that random copolymerization is a simple but effective strategy to obtain new conductive copolymers as high-performance thermoelectric materials. By using a polymerizing acceptor unit diketopyrropyrrole with donor units thienothiophene and oligo ethylene glycol substituted bithiophene (g(3)2T), it is found that strong interchain donor-acceptor interactions ensure good film crystallinity for charge transport, while donor-donor type building blocks contribute to effective charge transfers. Hall effect measurements show that the high electrical conductivity results from increased free carriers with simultaneously improved mobility reaching over 1 cm(2)V(-1)s(-1). The synergistic effect of improved molecular doping and carrier mobility, as well as a high Seebeck coefficient ascribed to the structural disorder along polymer chains via random copolymerization, results in an impressive power factor up to 110 mu W K(-2)m(-1)which is 10 times higher than that of solution-processed polythiophenes.