Unconventional Doping Effect Leads to Ultrahigh Average Thermoelectric Power Factor in Cu₃SbSe₄‐Based Composites

Abstract

the dimensionless figure of merit zT = PF•T/κ = α 2 σT/(κ e + κ L ), where α, σ, T, κ e , and κ L are the Seebeck coefficient, electrical conductivity, absolute temperature, and electronic and lattice contributions to the total thermal conductivity, respectively. [3] PF denotes the TE power factor that characterizes electrical transport performance. In practice, the average power factor (PF avg ) is directly proportional to the output power density of TE devices. [4] Therefore, for practical application, a higher PF avg is more desirable for achieving a large output power. In principle, PF and PF avg are both determined by electronic band structure and optimal carrier concentration. [5][6][7] Several strategies have been proposed to enhance both PF and PF avg . For example, Pei et al. [8] showed that a high peak PF can be achieved in PbTe by increasing the band degeneracy; Zhu et al. [9] demonstrated that FeNb 1−x Ti x Sb reaches high PF via reducing band effective mass, which results in high carrier mobility. In recent years, it has been elucidated that grain boundaries also play an important role in carrier scattering for certain TE compounds. For instance, Zhao et al. [10,11] revealed that both p and n-type SnSe single crystals that are free of grain boundaries exhibit high PFs; Snyder et al. [12,13] discovered that PF of Mg 3 Sb 2 -based Thermoelectric materials are typically highly degenerate semiconductors, which require high carrier concentration. However, the efficiency of conventional doping by replacing host atoms with alien ones is restricted by solubility limit, and, more unfavorably, such a doping method is likely to cause strong charge-carrier scattering at ambient temperature, leading to deteriorated electrical performance. Here, an unconventional doping strategy is proposed, where a small trace of alien atoms is used to stabilize cation vacancies in Cu 3 SbSe 4 by compositing with CuAlSe 2 , in which the cation vacancies rather than the alien atoms provide a high density of holes. Consequently, the hole concentration enlarges by six times but the carrier mobility is well maintained. As a result, a record-high average power factor of 19 µW cm −1 K −2 in the temperature range of 300-723 K is attained. Finally, with further reduced lattice thermal conductivity, a peak zT value of 1.4 and a record-high average zT value of 0.72 are achieved within the diamond-like compounds. This new doping strategy not only can be applied for boosting the average power factor for thermoelectrics, but more generally can be used to maintain carrier mobility for a variety of semiconductors that need high carrier concentration.

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

“…10 In the past decades, a number of methods were carried out to increase the PF and PF ave , including adjusting the carrier concentration (n) and optimization of electronic band engineering, which were mainly achieved by doping. 11−15 Recently, we found that ternary copper-based tetrahedral structure compounds are deemed to be very promising TE materials due to their make of nontoxic constituent elements (tellurium-free) and excellent performance, such as Cu 3 SbSe 4 8,13 and Cu 2 SnSe 3 16,17 to name but a few. Among them, the Cu 2 GeSe 3 compound has attracted the increasing attention of researchers in recent years.…”

“…Therefore, a larger PF ave value is more suitable for obtaining a higher output power in practical applications . In the past decades, a number of methods were carried out to increase the PF and PF ave , including adjusting the carrier concentration ( n ) and optimization of electronic band engineering, which were mainly achieved by doping. − …”

Significantly Enhanced Thermoelectric Performance Achieved in CuGaTe2 through Dual-Element Permutations at Cation Sites

“…Up to now, the strategies that are used to improve the performance of thermoelectric (TE) materials fall into two categories. One is to aim to improve the power factor PF via carrier concentration optimization, − valence band convergence, , crystal structure modulation, , density of state (DOS) resonance, − and energy filtering , and the other focuses more on reducing the lattice thermal conductivity κ lat by various approaches such as alloying, , discordant atoms, , nanostructuring, − and twinning …”

Entropy Engineering in Tellurium-Free Thermoelectric Cu8GeSe6 with a Stable Cubic Structure

“…Here, σ, S , κ e , κ L , and T stand for electrical conductivity, Seebeck coefficient, electronic and lattice thermal conductivity, and the absolute temperature, respectively . The high zT performance can be obtained by either increasing the power factor (PF = σ S 2 ) or reducing thermal conductivity. , For the purpose of promoting TE performance, the electrical properties can be promoted by carrier concentration optimization and energy band engineering , while lattice thermal conductivity can be suppressed by strengthening phonon scattering through defects , and boundaries and nanostructuring. , However, due to the strong coupling between σ, S , and κ, it is difficult to optimize these parameters simultaneously to obtain high zT values.…”