Thermoelectric Performance of Tetrahedrite (Cu12Sb4S13) Thin Films: The Influence of the Substrate and Interlayer

Abstract

In the present work, tetrahedrite Cu₁₂Sb₄S₁₃ thin films were deposited on various substrates via aerosol-assisted chemical vapor deposition (AACVD) using diethyldithiocarbamate complexes as precursors. A buffer layer of Sb₂O₃ with a small lattice mismatch to Cu₁₂Sb₄S₁₃ was applied to one of the glass substrates to improve the quality of the deposited thin film. The buffer layer increased the coverage of the Cu₁₂Sb₄S₁₃ thin film, resulting in improved electrical transport properties. The growth of the Cu₁₂Sb₄S₁₃ thin films on the other substrates, including ITO-coated glass, a SiO₂-coated Si wafer, and mica, was also investigated. Compared to the films grown on the other substrates, the Cu₁₂Sb₄S₁₃ thin film deposited on the SiO₂-coated Si wafer showed a dense and compact microstructure and a larger grain size (qualities that are beneficial for carrier transport), yielding a champion power factor (PF) of ∼362 μW cm^-1 K^-2 at 625 K. The choice of substrate strongly influenced the composition, microstructure, and electrical transport properties of the deposited Cu₁₂Sb₄S₁₃ thin film. At 460 K, the highest zT value that was obtained for the thin films was ∼0.18. This is comparable to values reported for Cu-Sb-S bulk materials at the same temperature. Cu₁₂Sb₄S₁₃ thin films deposited using AACVD are promising for thermoelectric applications. To the best of our knowledge, the first full thermoelectric characterization of the Cu₁₂Sb₄S₁₃ thin film is performed in this work.

Figure 1

Grazing incidence X-ray diffraction (GIXRD) patterns for (a) the different substrate materials (glass, Sb₂O₃-coated glass, ITO-coated glass, a SiO₂-coated Si wafer, and mica) and (b) the Cu₁₂Sb₄S₁₃ thin films on these substrates.

Figure 2

Content fractions of the phases in the thin films deposited on the following different substrates: glass, Sb₂O₃-coated glass, ITO-coated glass, a SiO₂-coated Si wafer, and mica.

Figure 3

Scanning electron microscopy (SEM) images of the Cu₁₂Sb₄S₁₃ thin films on the following different substrates: (a) glass, (b) Sb₂O₃-coated glass, (c) ITO-coated glass, (d) mica, and (e) a SiO₂-coated Si wafer.

Figure 4

(a) High-resolution transmission electron microscopy (HRTEM) image of Cu₁₂Sb₄S₁₃ on the Sb₂O₃-coated glass substrate, and an inverse FFT image of the labeled white area (inset). (b) Selected area electron diffraction (SAED) pattern for the area in (a). (c) Ball model of Cu₁₂Sb₄S₁₃.

Figure 5

Temperature-dependent (a) electrical conductivity σ, (b) Seebeck coefficient S, and (c) power factor PF data for the Cu₁₂Sb₄S₁₃ thin films deposited on the following different substrates: glass, Sb₂O₃-coated glass, ITO-coated glass, a SiO₂-coated Si wafer, and mica. The uncertainties in the obtained Seebeck coefficients, electrical conductivities, and power factors were estimated to be 5%, 3%, and 10%, respectively. (d) Comparison of PF in this work to previously published data for Cu₁₂Sb₄S₁₃-based bulk materials.^,,−

Figure 6

(a) Temperature-dependent Seebeck coefficient S, electrical conductivity σ, and power factor PF data, and (b) temperature-dependent thermal conductivity κ, electronic thermal conductivity κ_e, and figure of merit zT data for the Cu₁₂Sb₄S₁₃ thin film deposited on a TFA test chip with a 300 nm Si₃N₄ membrane. The uncertainties in the obtained Seebeck coefficients, electrical conductivities, power factors, thermal conductivities, and zT values were estimated to be 7%, 6%, 15%, 10%, and 25%, respectively, according to Linseis et al.^, and eq 1.

Figure 7

Comparison of zT values for the Cu₁₂Sb₄S₁₃ thin film on the instrument-dedicated test chip obtained in this work with those for metal chalcogenide thin films reported in the past five years.⁻