Dual-Functional Electrochemically Synthesized Copolymers via Incorporating Bithiophene Units into 3,4-Ethylenedioxythiophene for Superior Thermoelectric and Charge Storage Performances

Free-standing or flexible substrate-supported poly(3,4-ethylenedioxythiophene) (PEDOT) films are much in demand due to their applications in various electronic, electrochromic, and thermoelectric devices. Prevalent methods of producing PEDOT free-standing films are from commercially available PEDOT:PSS, which has to be subjected to several pre- and post-treatments to tune the electrical and electrochemical properties. The present research focuses on developing dual-functional copolymer electrodes through the electrochemical polymerization of 2,2′-bithiophene (BTh) units with EDOT, aiming to enhance both thermoelectric properties and charge storage capabilities. By incorporating BTh units into the EDOT monomer, the copolymerization results in a significant change in morphological, structural, electrochemical, and electrical properties as well as improved stability, without any kind of pre- and post-treatments. This strategy serves dual purposes; it not only hinders polymer chains from forming coiled structures (and thus improves mobility) but also increases its electrochemical properties (and thereby charge storage capabilities). As a result of improved electrical and electrochemical properties, superior thermoelectric and capacitive properties are observed in copolymers compared to homopolymers. As-deposited copolymer films have approximately an order of magnitude enhancement in the mass specific capacitance (274 F/g) and thermoelectric power factor (11.5 μW/mK²) as compared to that of PEDOT films. The prepared films were free-standing and could be transferred onto solid substrates. The copolymerization method can be adopted as an alternative strategy to tune the electrical/electrochemical properties of polymers and opens a pathway to enable self-powered devices.