Enhanced Thermoelectric Performance in Polypyrrole-Based Multilayer Nanoarchitectures via Thermal Reduction

In this study, cationic polypyrrole nanoparticles (PPy:NPs) are synthesized in a water-based solution in order to serve as a template that facilitates the formation of flexible hierarchical structures, ultimately resulting in improved thermoelectric (TE) performance. A unique multilayered structure is fabricated by alternately depositing positively charged PPy:NPs and negatively charged double-walled carbon nanotube-graphene oxide (DWNT-GO) suspensions via layer-by-layer deposition. The resulting polymer/carbon composite, consisting of a 16-bilayer PPy:NPs/DWNT-GO with a thickness of approximately 2.45 μm, exhibited an electrical conductivity of 1.36 S/cm and a Seebeck coefficient of 84 μV/K, yielding a power factor of 0.96 μW/m·K2. A thermal reduction process at 175 °C for 90 min significantly enhanced the electrical conductivity (183.2 S/cm) and Seebeck coefficient (115 μV/K), resulting in a remarkable power factor of 242.2 μW/m·K2. This is one of the highest values ever reported for PPy-based organic TE materials. The outstanding TE properties can be attributed to the creation of a highly organized three-dimensional conjugated network after thermal reduction, which promotes carrier transport within the multilayers.