Cyclopentadithiophene-based Conjugated Polymers for Organic Thermoelectric Devices and Other Applications

The 4H-cyclopenta[2,1-b:3,4-b’]dithiophene (CPDT)-based conjugated polymers (CPs) have garnered significant attention in various fields of organic electronics due to their strong electron-donating properties, extended π-plane, and rigid, planar chemical structure. These unique features enable CPDT-based CPs to be highly advantageous for use in a range of organic semiconductor devices. While CPDT-based CPs have been extensively investigated and utilized as electron donors in various organic semiconductor devices, there is limited literature discussing the electrochemical properties of CPDT building blocks and the representative examples of CPDT-based CPs. In this mini-review, the authors outline the electrochemical properties of the CPDT building block, which stem from its rigid and planar chemical structure, facilitating the use of CPDT derivative materials in the field of organic semiconductors, such as organic photovoltaics (OPVs), organic thin film transistors (OTFTs), and organic photodetectors (OPDs). Furthermore, the authors highlight the advantages of CPDT-based CPs, particularly, for organic thermoelectric applications (OTEs) such as strong electron-donating properties and extended π-conjugation, which lead to facile p-type doping characteristics in CPDT-based CPs. The authors discuss the basic working principles of OTEs, including several key parameters of OTE devices such as the Seebeck coefficient (S) and power factor (PF). Additionally, the authors address the main challenge in OTEs: the trade-off relationship between electrical conductivity and the Seebeck coefficient. The review presents several strategies to overcome these trade-off limitations, focusing on CPDT and other CPs for OTE applications.