Conductive, Solution-Processed Dioxythiophene Copolymers for Thermoelectric and Transparent Electrode Applications

Conjugated polymers with high electrical conductivities are attractive for applications in capacitors, biosensors, organic thermoelectrics, and transparent electrodes. Here, a series of solution processable dioxythiophene copolymers based on 3,4-propylenedioxythiophene (ProDOT) and 3,4-ethylenedioxythiophene (EDOT) is investigated as thermoelectric and transparent electrode materials. Through structural manipulation of the polymer repeat unit, the conductivity of the polymers upon oxidative solution doping is tuned from 1 x 10(-3) to 3 S cm(-1), with a polymer consisting of a solubilizing alkylated ProDOT unit and an electron-rich biEDOT unit (referred to as PE2) showing the highest electrical conductivity. Optimization of the film casting method and screening of dopants result in AgPF6-doped PE2 achieving a high electrical conductivity of over 250 S cm(-1) and a thermoelectric power factor of 7 mu W m(-1) K-2. Oxidized spray cast films of PE2 are also assessed as a transparent electrode material for use with another electrochromic polymer. This bilayer shows reversible electrochemical switching from a colored charge-neutral state to a highly transmissive color-neutral, oxidized state. These results demonstrate that dioxythiophene-based copolymers are a promising class of materials, with ProDOT-biEDOT serving as a soluble analog to the well-studied PEDOT as a p-type thermoelectric and electrode material.