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

Abstract

We fabricated cast films of complexes of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid (PEDOT:PSS) at various thicknesses, t = 3–20 μm, 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 ∼20 μm on a polyimide substrate were ∼15 μV/K and 500 S/cm, respectively, near room temperature. As the film thickness decreased from ∼10 μm to 3 μm, 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 μm was 1.3 μW at ΔT = 100 K. Its open-circuit voltage was 7.3 mV, and its internal resistance was 11 Ω. 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 ΔT = 100 K as ∼650 μW/cm2 for a film thickness t = 10 μm, and 1400 μW/cm2 for t = 3 μm.