Paintable Thermoelectric Materials from Polymer Blends of Exfoliated 2D Nanosheets

In bulk form the thermoelectric material bismuth telluride (Bi₂Te₃) has a high figure of merit (ZT) at room temperature. When bulk Bi₂Te₃ is exfoliated to smaller dimensions, such as its 2D form (nanosheets), its thermoelectric effects are improved by reduction in thermal conductivity due to phonon confinement and scattering, thus increasing the ZT. The difficulty involved in incorporating nanosheets into energy harvesting systems motivated the search for a form of Bi₂Te₃ that retains the high ZT apparent at the nanoscale with the capability of being deposited or painted onto device infrastructures.

This work highlights a method whereby solvent exfoliation of Bi₂Te₃ into solution-dispersible 2D nanosheets can form a practical thin film that can be distributed across a surface. Optical transmission measurements quantify the relationship between efficient and stable exfoliation and the reduction in optical density. Optimized exfoliated suspension are also shown to form smooth, uniform blends when mixed with poly ethylene glycol and other polymers to produce a paintable Bi₂Te₃film that can be applied to surfaces using an innovative painting technique.

Atomic force microscopy, transmission electron spectroscopy, Raman spectroscopy and scanning electron spectroscopy are used to examine the structure of the 2D nanosheets and the highly reproducible Bi₂Te₃ thin films. Electrical transport studies show that the films have conductive pathways over a range of surfaces and various structural formations, linking the conductivity to the percolating conduction through the nanosheet ensemble. The combination of the facile preparation method and the scope for diverse surface coating as a cohesive and conductive thin film offers a methods for integration with heat producing devices for energy harvesting applications.

References

1. K. M. F. Shahil, M. Z. Hossain, D. Teweldebrhan and A. A. Balandin, Applied Physics Letters, 96 (2010).
2. B. Poudel, Q. Hao, Y. Ma, Y. Lan, A. Minnich, B. Yu, X. Yan, D. Wang, A. Muto, D. Vashaee, X. Chen, J. Liu, M. S. Dresselhaus, G. Chen and Z. Ren, Science, 320, 634 (2008).
3. M. Saleemi, M. S. Toprak, S. Li, M. Johnsson and M. Muhammed, Journal of Materials Chemistry, 22, 725 (2012).
4. L. E. Bell, Science, 321, 1457 (2008).
5. S. Li, M. S. Toprak, H. M. A. Soliman, J. Zhou, M. Muhammed, D. Platzek and E. Müller, Chemistry of Materials, 18, 3627 (2006).
6. Y. Hernandez, N. Valeria, L. Mustafa, B. F. M., S. Zhenyu, S. De, M. T., B. Holland, M. Byrne, Y. K. Gun'Ko, J. J. Boland, P. Niraj, G. Duesberg, S. Krishnamurthy, R. Goodhue, J. Hutchison, V. Scardaci, A. C. Ferrari and J. N. Coleman, Nature Nanotechnology, 3, 1748 (2008).
7. V. Nicolosi, M. Chhowalla, M. G. Kanatzidis, M. S. Strano and J. N. Coleman, Science, 340 (2013).
8. L. D. Hicks and M. S. Dresselhaus, Physical Review B, 47, 12727 (1993).