Chemistry in Advancing Thermoelectric GeTe Materials

Abstract

Metrics & MoreArticle Recommendations CONSPECTUS:The ever-growing energy crisis and the deteriorated environment caused by carbon energy consumption motivate the exploitation of alternative green and sustainable energy supplies. Because of the unique advantages of zero-emission, no moving parts, accurate temperature control, a long steady-state operation period, and the ability to operate in extreme situations, thermoelectrics, enabling the direct conversion between heat and electricity, is a promising and sustainable option for power generation and refrigeration. However, with increasing application potentials, thermoelectrics is now facing a major challenge: developing high-performance, Pb-free, and lowtoxic thermoelectric materials and devices.As one group of promising candidates, GeTe derivatives have the potential to replace the widely used thermoelectric materials containing highly toxic elements.In this Account, we summarize our recent progress in developing highperformance GeTe-based thermoelectric materials via exploring innovative strategies to enhance electron transports and dampen phonon propagations. First, we fundamentally illustrate the underlying chemistry and physical reason for an intrinsically high carrier concentration in GeTe, which enormously restrains the thermoelectric performance of GeTe. From our theoretical calculations, the formation energy of Ge vacancy is the lowest among the defects in GeTe, energetically favoring Ge vacancies in the lattice and leading to intrinsically high carrier concentrations. Accordingly, aliovalent doping/alloying is proposed to increase the formation energy of Ge vacancies and decrease the carrier concentration to the optimal level. We then outline the newly developed method to refine the band structures of GeTe with tuned electronic transport. On the basis of the molecular orbital theory, the energy offset between two valence band edges at the L and Σ points in GeTe should be ascribed to the slightly different Ge_4s orbital characters at these two points, which guides the screening of dopants for band convergence. Besides, the Rashba spin splitting is explored to increase the band degeneracy of GeTe. Afterward, we analyze the dampened phonon propagation in GeTe to minimize its lattice thermal conductivity. Alloying with the heavy Sb atoms can shift the optical phonon modes toward low frequency and reinforce the interaction of optical and acoustic phonon modes so that the inherent phonon scattering is enhanced. In addition, planar vacancies and superlattice precipitates can significantly strengthen phonon scattering to result in ultralow lattice thermal conductivity. After that, we overview the finite elemental analysis simulations to optimize the device geometry for maximizing the device performance and introduce the as-developed prototype GeTe-based thermoelectric device. In the end, we point out future directions in the development of GeTe for device applications. The strategies summarized in this Account can serve as references for developing wide materi...

Grain Boundary Complexions Enable a Simultaneous Optimization of Electron and Phonon Transport Leading to High‐Performance GeTe Thermoelectric Devices

“…The obtained B factor is comparable to other GeTe‐based compounds doped with Ta, V, Cu, Cd, and I. [ 58 ]…”

“…The obtained B factor is comparable to other GeTe-based compounds doped with Ta, V, Cu, Cd, and I. [58] As summarized in Figure 2d, the enhancement of ZT follows the trend of the B factor depending on the doping elements. Introducing appropriate Ga (1%) in conjunction with the optimization of n by Sb alloying is quite efficient in enhancing ZT at high temperatures while substituting Ge by Pb is especially useful for improving ZT in the lower temperature range.…”

Single-atom thermoelectric materials: a new opportunity

“…However, so far SAMs have scarcely been applied or investigated in the thermoelectric field. Thermoelectric (TE) materials, enabling the straightforward and reversible conversion between heat and electricity, have attracted particular attention due to their environmentfriendly applications in waste heat power generation and refrigeration [10,11] . The conversion efficiency of TE materials or devices can be evaluated by the dimensionless figure of merit ZT, defined as ZT=S 2 σT/(κ L +κ e ) [12,13] , where S, σ, κ L , κ e , and T are the Seebeck coefficient, the electrical conductivity, the lattice thermal conductivity, the electronic thermal conductivity, and the absolute temperature respectively.…”

Advances in Versatile GeTe Thermoelectrics from Materials to Devices

“…New developed theoretical calculations have been used to screen the suitable dopants for band convergence. [200,232] Figure 11d plots the band structure of C-GeTe and the contributions to band structures of atomic orbitals as the dots. The magnitude of atomic orbital contribution is proportional to the spot size.…”