Tin-substituted chalcopyrite: an n-type sulfide with enhanced thermoelectric performance

Tippireddy, S., Azough, F., Vikram, V., Towers Tompkins, F., Bhui, A., Freer, R., Grau-Crespo, R. ORCID: https://orcid.org/0000-0001-8845-1719, Biswas, K., Vaqueiro, P. ORCID: https://orcid.org/0000-0001-7545-6262 and Powell, A. V. (2022) Tin-substituted chalcopyrite: an n-type sulfide with enhanced thermoelectric performance. Chemistry of Materials, 34 (13). pp. 5860-5873. ISSN 1520-5002 doi: 10.1021/acs.chemmater.2c00637

Abstract/Summary

The dearth of n-type sulfides with thermoelectric performance comparable to that of their p-type analogues presents a problem in the fabrication of all-sulfide devices. Chalcopyrite (CuFeS2) offers a rare example of an n-type sulfide. Chemical substitution has been used to enhance the thermoelectric performance of chalcopyrite through preparation of Cu1 xSnxFeS2 (0 ≤ x ≤ 0.1). Substitution induces a high level of mass and strain-field fluctuation, leading to lattice softening and enhanced point-defect scattering. Together with dislocations and twinning identified by transmission electron microscopy, this provides a mechanism for scattering phonons with a wide range of mean free paths. Substituted materials retain a large density-of-states effective mass, and hence a high Seebeck coefficient. Combined with a high charge-carrier mobility, and thus high electrical conductivity, a 3-fold improvement in power factor is achieved. Density functional theory (DFT) calculations reveal that substitution leads to the creation of small polarons, involving localised Fe2+ states, as confirmed by X-ray photoelectron spectroscopy. Small polaron formation limits the increase in carrier concentration to values that are lower than expected on electron-counting grounds. An improved power factor, coupled with substantial reductions (up to 40 %) in lattice thermal conductivity, increases the maximum figure-of-merit by 300%, to zT  0.3 at 673 K for Cu0.96Sn0.04FeS2.

Item Type	Article
URI	https://reading-clone.eprints-hosting.org/id/eprint/105694
Item Type	Article
Refereed	Yes
Divisions	Interdisciplinary centres and themes > Chemical Analysis Facility (CAF) Life Sciences > School of Chemistry, Food and Pharmacy > Department of Chemistry
Publisher	American Chemical Society
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