Novel Hybrid p- and n-Type Organic Thermoelectric Materials Based on Mussel-Inspired Polydopamine

Mussel-inspired polydopamine (PDA) can serve as building blocks and interfaces in designing functional materials. Here, the use of PDA as an interlayer between polyaniline (PANi) and multidimensional carbon materials, such as graphene quantum dots (GQD), multiwalled carbon nanotubes (MWCNT), and graphene nanosheets (GNS), to improve the thermoelectric performance of p-type polymer-based materials has been reported. The introduction of PDA promotes the carrier mobility of GQD/PDA/PANi, CNT/PDA/PANi, and GNS/PDA/PANi ternary composites due to the superior adhesive property of PDA. An optimal conductivity of 4.98 × 10⁴ S m^-1 and a power factor of 92.17 μW m^-1 K^-2 at 363 K are achieved in GNS/PDA/PANi, which are much higher than the values of GNS/PDA and GNS/PANi. More surprisingly, despite the fact that GQD/PDA, CNT/PDA, and GNS/PDA binary composites show p-type properties, the pyrolysis treatment of GQD/PDA, CNT/PDA, and GNS/PDA at 800 °C results in a gain in both the electrical conductivity and negative Seebeck coefficient of c-GQD/PDA, c-CNT/PDA, and c-GNS/PDA. The c-CNT/PDA composites possess the highest Seebeck value of -30.2 μV K^-1 and a maximum power factor value of 35.57 μW m^-1 K^-2. Finally, a flexible thermoelectric generator with 24 thermoelectric units composed of GNS/PDA/PANi and c-CNT/PDA is demonstrated, which gives an output voltage of 52.8 mV at a temperature difference of 60 °C.