Enhanced Thermoelectric Properties in Bulk Nanowire Heterostructure-Based Nanocomposites through Minority Carrier Blocking

Abstract

To design superior thermoelectric materials the minority carrier blocking effect in which the unwanted bipolar transport is prevented by the interfacial energy barriers in the heterogeneous nanostructures has been theoretically proposed recently. The theory predicts an enhanced power factor and a reduced bipolar thermal conductivity for materials with a relatively low doping level, which could lead to an improvement in the thermoelectric figure of merit (ZT). Here we show the first experimental demonstration of the minority carrier blocking in lead telluride–silver telluride (PbTe–Ag_2Te) nanowire heterostructure-based nanocomposites. The nanocomposites are made by sintering PbTe–Ag_2Te nanowire heterostructures produced in a highly scalable solution-phase synthesis. Compared with Ag_2Te nanowire-based nanocomposite produced in similar method, the PbTe–Ag_2Te nanocomposite containing ∼5 atomic % PbTe exhibits enhanced Seebeck coefficient, reduced thermal conductivity, and ∼40% improved ZT, which can be well explained by the theoretical modeling based on the Boltzmann transport equations when energy barriers for both electrons and holes at the heterostructure interfaces are considered in the calculations. For this p-type PbTe–Ag_2Te nanocomposite, the barriers for electrons, that is, minority carriers, are primarily responsible for the ZT enhancement. By extending this approach to other nanostructured systems, it represents a key step toward low-cost solution-processable nanomaterials without heavy doping level for high-performance thermoelectric energy harvesting.

Additional Information

© 2015 American Chemical Society. Received: December 2, 2014; Revised: December 23, 2014; Published: January 9, 2015. Y.W. led the project. H.Y. was the main contributor for the PbTe−Ag_2Te heterostructure synthesis, nanocomposite fabrications, and structural characterizations. J.-H.B. and A.S. performed the theoretical modeling. T.D. and G.J.S. performed the electrical conductivity measurements. H.Y. and A.M.S.M. performed Seebeck coefficient measurements. Funding: This work is supported by US Air Force Office of Scientific Research (Award Number FA9550-12-1-0061).

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Supplemental Material - nl504624r_si_001.pdf

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