Thermoelectric Power-Generation Characteristics of PEDOT:PSS Thin-Film Devices with Different Thicknesses on Polyimide Substrates

We fabricated cast films of complexes of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid (PEDOT:PSS) at various thicknesses, t = 3-20 mu m, on flexible polyimide substrates, and studied their thermoelectric properties. We also fabricated in-plane film devices consisting of five couples of PEDOT:PSS and Ag electrodes, measuring their output power characteristics as a function of film thickness. The Seebeck coefficient and electrical conductivity of a PEDOT:PSS film with a thickness of similar to 20 mu m on a polyimide substrate were similar to 15 mu V/K and 500 S/cm, respectively, near room temperature. As the film thickness decreased from similar to 10 mu m to 3 mu m, the electrical conductivity increased remarkably to 1200 S/cm, while the Seebeck coefficient remained almost constant with film thickness. The maximum electric power for an in-plane PEDOT:PSS film device with a thickness of 10 mu m was 1.3 mu W at Delta T = 100 K. Its open-circuit voltage was 7.3 mV, and its internal resistance was 11 Omega. The measured power-generation characteristics of the film device agreed with values estimated from the dependence of thermoelectric properties on film thickness for PEDOT:PSS films on polyimide substrates. Assuming single PEDOT:PSS legs, defined as the direction of heat transport, we estimated the expected electrical power density at Delta T = 100 K as similar to 650 mu W/cm(2) for a film thickness t = 10 mu m, and 1400 mu W/cm(2) for t = 3 mu m.