Recent Progress in Multiphase Thermoelectric Materials

Abstract

Thermoelectric materials, which directly convert thermal energy to electricity and vice versa, are considered a viable source of renewable energy. However, the enhancement of conversion efficiency in these materials is very challenging. Recently, multiphase thermoelectric materials have presented themselves as the most promising materials to achieve higher thermoelectric efficiencies than single-phase compounds. These materials provide higher degrees of freedom to design new compounds and adopt new approaches to enhance the electronic transport properties of thermoelectric materials. Here, we have summarised the current developments in multiphase thermoelectric materials, exploiting the beneficial effects of secondary phases, and reviewed the principal mechanisms explaining the enhanced conversion efficiency in these materials. This includes energy filtering, modulation doping, phonon scattering, and magnetic effects. This work assists researchers to design new high-performance thermoelectric materials by providing common concepts.

Thermoelectric performance of multiphase GeSe‐CuSe composites prepared by hydrogen decrepitation method

“…The pristine GeSe exhibits an S of 855 μV/K at 323 K and raised up to 1344 μV/K at 650 K, which is a relatively higher value than the previously reported value 30‐34 . Moreover, the similar structured pristine SnSe have exhibited a similar tendency of Seebeck coefficient variation in the measured temperature range 18,20 . Meanwhile, Increasing the Cu(x) content in Ge 1− x Cu x Se (0.1 ≤ x ≤ 0.3) samples decreased the S, which is mainly due to the following reason: (i) influence of multiphases occurring in the sample and (ii) enhancement in the carrier concentration.…”

“…GeSe is a known p‐type semiconductor (Eg = 1.1 to 1.2 eV), with orthorhombic ( Pnma symmetry ) crystal structure similar to SnSe at room temperature. It is noteworthy to mention that making materials with multiphase, where the heterojunction between the multiple phases with different band gaps and larger carrier density than the host matrix will greatly improve the electron transport properties 18 . The thermoelectric properties of Cu‐added multiphase GeSe materials have not been reported in detail 21 .…”

“…Several approaches have been made to reduce the κ L via low sound velocity, 1 rattling atom in voids, [2][3][4] liquid-like sublattice, [5][6][7][8] multiscale microstructures, [9][10][11][12][13] and anharmonicity. [14][15][16][17] The power factor can be improved by multiphase, 18 alloying effect, 19 resonant levels, 20 band structure engineering, 21 and band convergence. [22][23][24][25][26][27] The ZT and energy conversion efficiency of the thermoelectric materials can be optimized by modifying the electronic and thermal properties.…”

“…It is noteworthy to mention that making materials with multiphase, where the heterojunction between the multiple phases with different band gaps and larger carrier density than the host matrix will greatly improve the electron transport properties. 18 The thermoelectric properties of Cu-added multiphase GeSe materials have not been reported in detail. 21 Moreover, GeSe has been useful in other applications such as photovoltaic, 33 photonic devices with thin-film structure, 34,35 resistive memory cells, 36 optoelectronics, 37,38 and electrochemical memory cells.…”

Review on grain size effects on thermal conductivity in ZnO thermoelectric materials

“…A reduction in the thermal conductivity of the lattice as a result of the scattering of phonons by nanostructuring 97,98 was one of the mechanisms for improving the thermoelectric performance of materials. 98,99 Studies showed that the grain size distribution influences the design parameters for the development of materials with superior properties and few researchers 100–102 reported this can be done through inexpensive apparatus set to suit a wide range of applications. Another effective technique used to adjust nanostructure morphology/size of ZnO was using microwave irradiation and has been found by in providing highly efficient TE materials.…”