Optimization of the thermoelectric figure of merit in the conducting polymer poly(3,4-ethylenedioxythiophene)

Organic materials are rarely considered for thermoelectric applications, because their low electrical conductivity limits the thermoelectric figure of merit (ZT). It is now shown that by optimizing the oxidation level in a polymer, ZT can reach 0.25, which approaches the values desirable for devices. Thermoelectric generators (TEGs) transform a heat flow into electricity. Thermoelectric materials are being investigated for electricity production from waste heat (co-generation) and natural heat sources. For temperatures below 200 °C, the best commercially available inorganic semiconductors are bismuth telluride (Bi 2 Te 3 )-based alloys, which possess a figure of merit ZT close to one 1 . Most of the recently discovered thermoelectric materials with ZT>2 exhibit one common property, namely their low lattice thermal conductivities 2 , 3 . Nevertheless, a high ZT value is not enough to create a viable technology platform for energy harvesting. To generate electricity from large volumes of warm fluids, heat exchangers must be functionalized with TEGs. This requires thermoelectric materials that are readily synthesized, air stable, environmentally friendly and solution processable to create patterns on large areas. Here we show that conducting polymers might be capable of meeting these demands. The accurate control of the oxidation level in poly(3,4-ethylenedioxythiophene) (PEDOT) combined with its low intrinsic thermal conductivity ( λ =0.37 W m −1 K −1 ) yields a ZT=0.25 at room temperature that approaches the values required for efficient devices.