High Thermoelectric Performance in Chalcopyrite Cu_1–xAg_xGaTe₂–ZnTe: Nontrivial Band Structure and Dynamic Doping Effect

Abstract

The understanding of thermoelectric properties of ternary I− III−VI 2 type (I = Cu, Ag; III = Ga, In; and VI = Te) chalcopyrites is less well developed. Although their thermal transport properties are relatively well studied, the relationship between the electronic band structure and charge transport properties of chalcopyrites has been rarely discussed. In this study, we reveal the unusual electronic band structure and the dynamic doping effect that could underpin the promising thermoelectric properties of Cu 1−x Ag x GaTe 2 compounds. Density functional theory (DFT) calculations and electronic transport measurements suggest that the Cu 1−x Ag x GaTe 2 compounds possess an unusual non-parabolic band structure, which is important for obtaining a high Seebeck coefficient. Moreover, a mid-gap impurity level was also observed in Cu 1−x Ag x GaTe 2 , which leads to a strong temperature-dependent carrier concentration and is able to regulate the carrier density at the optimized value for a wide temperature region and thus is beneficial to obtaining the high power factor and high average ZT of Cu 1−x Ag x GaTe 2 compounds. We also demonstrate a great improvement in the thermoelectric performance of Cu 1−x Ag x GaTe 2 by introducing Cu vacancies and ZnTe alloying. The Cu vacancies are effective in increasing the hole density and the electrical conductivity, while ZnTe alloying reduces the thermal conductivity. As a result, a maximum ZT of 1.43 at 850 K and a record-high average ZT of 0.81 for the Cu 0.68 Ag 0.3 GaTe 2 −0.5%ZnTe compound are achieved.

Unraveling the role of chemical composition in the lattice thermal conductivity of oxychalcogenides as thermoelectric materials

“…For instance, Xie et al have found that Cu 1− x Ag x GaTe 2 alloys present an unusual non-parabolic band structure, which is crucial for obtaining a high Seebeck coefficient. 60…”

“…For instance, Xie et al have found that Cu 1Àx Ag x GaTe 2 alloys present an unusual nonparabolic band structure, which is crucial for obtaining a high Seebeck coefficient. 60 Moreover, the substitution of Ag by Cu favors the presence of carriers, which is benecial to obtaining higher power factors. 61,62 Although the calculation of ZT is out of the scope of this work, it is possible to anticipate that BiOAg 0.5 Cu 0.5 Se is a potential candidate as thermoelectric material.…”

Enhanced Thermoelectric Efficiency through Li-Induced Phonon Softening in CuGaTe2

“…The latter led to significant zT improvements of 1.0 due to a reduction of the lattice thermal conductivity. Alloying CuGaTe 2 with Ag and ZnTe enhances zT further to a maximum value of 1.43 . Here, we synthesized and measured the thermoelectric properties of unlithiated and lithiated CuGaTe 2 , CuGaTe 1.99 Sb 0.01 , and Cu 0.95 Ag 0.05 GaTe 2 .…”

“…Alloying CuGaTe 2 with Ag and ZnTe enhances zT further to a maximum value of 1.43. 28 Here, we synthesized and measured the thermoelectric properties of unlithiated and lithiated CuGaTe 2 , CuGaTe 1.99 Sb 0.01 , and Cu 0.95 Ag 0.05 GaTe 2 . The experimental data were compared to first-principles calculations to gain a deeper understanding of the underlying physics of the thermoelectric transport properties.…”

Incompletely Decomposed In4SnSe4 Leads to High‐Ranged Thermoelectric Performance in n‐Type PbTe

“…One is alloying or doping impurity elements, like Pb‐alloyed SnSe, [ 3a,9 ] Se‐alloyed PbTe, [ 10 ] and Cd‐doped AgSbTe 2 [ 11 ] . The other is introducing second phases, like MnTe‐Sb 2 Te 3 , [ 12 ] CuGaTe 2 ‐Ag 2 Te, [ 13 ] and PbSe‐SiO 2 . [ 14 ] Generally, the elemental doping and alloying mainly optimize the electrical transport by tuning the carrier density and mobility or modifying the electronic band structure, while the induced second phases contribute to suppressing the thermal transport by strengthening the defects‐phonon scattering.…”