Development of Thermally Induced Microstructure Gradient in Semiconducting Polymers for Functionally Graded Organic Thermoelectrics

Semiconducting polymers show great potential for organic thermoelectrics (OTEs) due to their intrinsically low thermal conductivity, high mechanical flexibility, broad chemical tunability, and ease of processing. Introducing charge carriers through chemical doping and optimizing structural properties like crystallinity or morphology are common strategies for increasing electrical conductivity and the thermoelectric power factor of OTEs. In this study, we utilized the poly(dodecyl-quaterthiophene) (PQT), which has different polymorphs obtained by controlling the thermal annealing process, through the sequential solution doping to get high thermoelectric performance. In addition, we can apply spatially microstructure control across the polymer film for potentially high thermoelectric performance functionally graded (FG) OTEs through a customized thermal annealing stage and sequential solution doping process. We also studied the surface morphology, the polymorph microstructure, and the relationship between doping level and thermoelectric properties by atomic force microscopy (AFM), grazing incidence wide angle X-ray scattering (GIWAXS), UV-Vis and Raman Spectroscopy. Ultimatlely, after fully understanding the procedure and the doping mechanism, we believe this study offers more insights that can improve the thermoelectric performance in organic materials and foster the application of low-cost energy harvesting and thermoelectric refrigeration devices.