A comprehensive investigation into thermoelectric properties of PEDOT:PSS/Bi0.5Sb1.5Te3 composites

Abstract

The demand for sustainable power sources for wearable electronic devices has spurred exploration into novel energy harvesting technologies. Among these, flexible thermoelectric (TE) materials and generators (TEGs) show promise for transforming body heat into electrical power. For this purpose, organic and polymeric semiconducting materials, such as poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), have been at the forefront of research recently due to their flexibility, nontoxicity, easy processability, high electrical conductivity, and low thermal conductivity. However, hybridization with inorganic materials, optimization of doping levels, and structural modifications to enhance their TE conversion efficiency are still ongoing areas of investigation, and a comprehensive study encompassing all these approaches is lacking. This research presents the first comprehensive and encyclopedic study of the TE properties of PEDOT:PSS thin films hybridized with Bi_0.5Sb_1.5Te₃ particles to explore the relationship between particle size/concentration, chemical post-treatment strategies, and the resulting microstructural, morphological, and TE properties. Initially, PEDOT:PSS was hybridized with Bi_0.5Sb_1.5Te₃ particles with a wide range of size (0.3–1.4 μm) and concentration (5–60 wt%), and the microstructure and TE properties of the resulting composite films were systematically studied. The composite with 40 wt% Bi_0.5Sb_1.5Te₃ particles exhibited the highest power factor at room temperature, was chosen as the optimal sample, and underwent various single and sequential chemical post-treatments using secondary dopants (DMSO, EG, H₂SO₄) and a dedoping agent (NaOH). While single post-treatment with 0.5 M H₂SO₄ could increase the power factor up to 240 times compared to the pristine composite, a sequential pos-treatment with 0.5 M H₂SO₄ and 0.1 M NaOH resulted in an 864-fold increase in the power factor at room temperature. Furthermore, the temperature-dependent electrical conductivity and Seebeck coefficient of the composite thin films were explored in each case (between 300 K and 375 K) to determine the dominant charge transport mechanism. It was revealed that the charge carrier transport mechanism was three-dimensional variable range hopping in pristine composite samples; however, metallic conduction was observed in the samples after sequential chemical post-treatment. The findings of this paper make it a thorough reference for understanding the TE properties of inorganic/polymeric composites, and offer a detailed perspective on strategies to optimize their power factor for applications in flexible TEGs.