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 5.3μWK−2m−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.

This study investigates the directional solidification behavior and the effects of initial freezing temperature on the formation of porous structure. The aqueous suspension with 10 vol.% cupric oxide (CuO) particles is prepared by mixing CuO particles, polyvinyl alcohol, and polyvinylpyrrolidone in deionized water. Additionally, potassium hydroxide is used to adjust the pH values between 8–10. Based on the measurement of the suspension viscosity, the optimal amount of the dispersant and the range of pH values that enable a well dispersed and stable suspension is identified. The freezing curves of the suspensions are measured to obtain the freezing point of the suspension as well as the effect of the potassium hydroxide on the freezing behavior. The suspensions then undergo directional freezing under various initial freezing temperatures. After sublimation under a near vacuum pressure, the green samples are infiltrated with epoxy to facilitate visualization and characterization of the pore morphology and orientation using an optical microscope. We believe that the obtained relationship between the freezing conditions, and the structural specifics of freeze-cast porous CuO lays the groundwork for freeze-cast porous copper with desirable pore morphology and structures for thermal management and energy storage applications.

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