Enhancement of the Thermoelectric Performance of Cu₂GeSe₃ via Isoelectronic (Ag, S)-co-substitution

Abstract

Recently, ternary Cu-based Cu-IV-Se (IV = Sb, Ge, and Sn) compounds have received extensive attention in the thermoelectric field. Compared with Cu-Sb-Se and Cu-Sn-Se, Cu-Ge-Se compounds have been less studied due to its poor Seebeck coefficient and high thermal conductivity. Here, the Cu 2 GeSe 3 material with high electrical conductivity was first prepared, and then, its effective mass was increased by doping with S, which led to the Seebeck coefficient of the doped sample being 1.93 times higher than that of pristine Cu 2 GeSe 3 at room temperature. Moreover, alloying Ag at the Cu site in the Cu 2 GeSe 2.96 S 0.04 sample could further cause a 5.16 times increase in the Seebeck coefficient at room temperature, and the lattice thermal conductivity was remarkably decreased because of the introduction of the dislocations in the Cu 2 GeSe 3 sample. Finally, benefitted from the high Seebeck coefficient and low thermal conductivity, a record high ZT = 0.9 at 723 K was obtained for the Cu 1.85 Ag 0.15 GeSe 2.96 S 0.04 sample, which increased 345% in comparison with the pristine Cu 2 GeSe 3 , and it is among the highest reported values for Cu 2 GeSe 3based thermoelectric.

A facile synthetic route toward phase-pure colloidal Cu2GeS3 nanostructures mediated through metal xanthate precursors

“…7 Cu 2 GeS 3 stands out due to its high absorption coefficient, good electronic properties arising from its large carrier concentration and high carrier mobility, and a direct band gap of 1.5-1.6 eV, all of which are highly desirable for single-junction solar cell applications. 1,8,9 In addition to photovoltaic application, Cu 2 GeS 3 has also been explored due to its thermoelectric performance, 10 as an anode material for lithium-ion batteries 11 and as a photocatalyst for hydrogen evolution from water. 12 Considering the importance of Cu 2 GeS 3 , various approaches have been adopted for its preparation.…”

Inducing High Power Factor in Cu2GeSe3-Based Bulk Materials via (Bi, Zn)-Co-doping

“…Finally, we achieved two relatively high PF values of 8.66 μW cm −1 K −2 in the Cu 1.988 Bi 0.01 Zn 0.002 GeSe 3 sample and 7.22 μW cm −1 K −2 in the Cu 1.986 Bi 0.01 Zn 0.004 GeSe 3 sample at 723 K, which were increased by 135 and 113% compared with the pristine Cu 2 GeSe 3 , respectively. As can be seen in Figure 8b, the highest PF value of the (Bi, Zn) co-doped Cu 2 GeSe 3 substrate was even higher than those of previously reported In-, 38 Cudeficient, 30 Ni-, 19 Ag−S-, 29 Ag−In-, 20 and Ag−Ga-doped 18 Cu 2 GeSe 3 substrates with high PF values.…”

“…At the same time, they μ enhanced from 15.4 ( x = 0) to 37.3 cm 2 V –1 s –1 ( x = 0.02) at room temperature. It is worth noting that the high n of the Cu 2 GeSe 3 substrate was associated with the vacancy of Ge. , According to σ = ne μ, the σ of the Cu 2– x Bi x GeSe 3 sample decreased, which was attributed to a decrease of n . Huang et al reported that the n value was obviously reduced from 6.5 × 10 19 cm –3 for pristine Cu 2 GeSe 3 to 1.97 × 10 19 cm –3 for Cu 2– x GeSe 3 sample at 300 K when x was increased to 0.1, and the decrease of n in the Cu 2– x GeSe 3 sample was originated from the increase of Cu vacancy .…”

“…It is worth noting that the high n of the Cu 2 GeSe 3 substrate was associated with the vacancy of Ge. 24,29 According to σ = neμ, the σ of the Cu 2−x Bi x GeSe 3 sample decreased, which was attributed to a decrease of n. Huang et al reported that the n value was obviously reduced from 6.5 × 10 19 cm −3 for pristine Cu 2 GeSe 3 to 1.97 × 10 19 cm −3 for Cu 2−x GeSe 3 sample at 300 K when x was increased to 0.1, and the decrease of n in the Cu 2−x GeSe 3 sample was originated from the increase of Cu vacancy. 30 Due to the electronegativity of Bi (2.01) larger than Cu (1.85), the doping of Bi on the Cu site in the Cu 2 GeSe 3 substrate inevitably contributed to a larger E g as seen in Figure S3, and the valence of Bi and Cu was different hereby raising the vacancy of Cu resulting in decreased n at room temperature.…”

THERMODYNAMIC PROPERTIES OF THE Cu2GeSe3 COMPOUND

“…In recent years, the copper germanium selenide, Cu 2 GeSe 3 compound and phases based on it, have been intensively studied as potential environmentally friendly thermoelectric and photovoltaic materials [11][12][13][14][15][16][17].…”