Contributions to composite conductivity and Seebeck coefficient in commercial Bi₂Te₃—Conjugated polymer composites

Abstract

We demonstrated the use of as-received conjugated polymer P3HT [poly (3-hexylthiophene-2,5 diyl)] doped with F4TCNQ (2,3,5,6- tetrafluoro-7,7,8,8-tetracyanoquinodimethane) as a matrix for forming a composite with as-received, commercially available p-type Bi2Te3 powder. The optimized formulation exhibits a power factor of up to 5:3 μWK⁻² m⁻¹, about nine times higher than the highest power factor that we achieved from mixtures of only P3HT and F4TCNQ. Bi2Te3 was responsible for increases in both the Seebeck coefficient and the electrical conductivity. P3HT, with a higher hole mobility, was superior to PQT-12 [poly(bisdodecylquaterthiophene)], and F4TCNQ was at least as good as FeCl3, for matrix and dopant, respectively, for this purpose. The power factor obtained is about 40% of that reportedly obtained from synthesized Bi2Te3 nanowires in FeCl3-doped P3HT. We calculated the expected contributions of the bulk Bi2Te3 to the composite conductivity and then examined the resistance caused by interfaces on four different size distributions of Bi2Te3 particles, as well as a solid macroscopic ingot. A nonlinear I–V relationship was found for the doped P3HT-ingot bilayer. While our doped conjugated polymer system made only from commercial-grade components was shown to support the extraction of thermoelectric performance by a commonly used inorganic semiconductor, our results also suggest that an advantage of the smallest Bi2Te3 domains, including nanowires, may arise from their having less interfacial resistance than larger Bi2Te3 particles and pieces.