Electrically Programmed Doping Gradients Optimize the Thermoelectric Power Factor of a Conjugated Polymer

• DOI: 10.1002/adfm.202312549
• Publication Date: 2024-01-24T13:55:35Z
• Authors: Jian Liu; Mariavittoria Cra...; Vandna K. Gupta; Dorothea Scheunemann; Sri Harish Kumar ...; Emmy Järsvall; Youngseok Kim; Kai Xu; Juan Sebastián Re...; L. Jan Anton Koster; Mariano Campoy‐Qu...; Martijn Kemerink; Anna Martinelli; Christian Müller
• Keywords: Functionally graded materials; conjugated polymer; Other Electrical Engineering, Electronic Engineering, Information Engineering; organic thermoelectrics; Conjugated polymer; Organic thermoelectrics; 02 engineering and technology; Chemical doping; Condensed Matter Physics; Counterion drift; Inorganic Chemistry; counterion drift; chemical doping; Materials Chemistry; 0210 nano-technology; functionally graded materials

AbstractFunctionally graded materials (FGMs) are widely explored in the context of inorganic thermoelectrics, but not yet in organic thermoelectrics. Here, the impact of doping gradients on the thermoelectric properties of a chemically doped conjugated polymer is studied. The in‐plane drift of counterions in moderate electric fields is used to create lateral doping gradients in films composed of a polythiophene with oligoether side chains, doped with 2,3,5,6‐tetrafluoro‐tetracyanoquinodimethane (F4TCNQ). Raman microscopy reveals that a bias voltage of as little as 5 V across a 50 µm wide channel is sufficient to trigger counterion drift, resulting in doping gradients. The effective electrical conductivity of the graded channel decreases with bias voltage, while an overall increase in Seebeck coefficient is observed, yielding an up to eight‐fold enhancement in power factor. Kinetic Monte Carlo simulations of graded films explain the increase in power factor in terms of a roll‐off of the Seebeck coefficient at high electrical conductivities in combination with a mobility decay due to increased Coulomb scattering at high dopant concentrations. Therefore, the FGM concept is found to be a way to improve the thermoelectric performance of not yet optimally doped organic semiconductors, which may ease the screening of new materials as well as the fabrication of devices.