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Symmetry and asymmetry in thermoelectrics

Thermoelectric technology has been investigated extensively as a kind of green energy, which can realize the direct conversion between heat and electricity. To increase the thermoelectric power efficiency, developing highly effective strategies for improving thermoelectric performance through synergistically optimizing electrical and thermal transport properties is urgently required. Recently, the manipulation of symmetry and asymmetry in thermoelectrics has been developed to enhance performance dramatically, which shows great potential in the thermoelectric field. In this perspective, we summarized these advanced achievements obtained through utilizing symmetry and asymmetry in thermoelectrics. Electrical transport properties can be improved effectively through increasing symmetry, which contributes to a higher carrier mobility and larger valley degeneracy. Asymmetry could induce lower lattice thermal conductivity due to the larger anharmonicity caused by hierarchical chemical bonding; similarly, lattice thermal conductivity can be effectively suppressed through reducing the symmetry. Finally, a discussion of future possible strategies is provided, aiming at further enhancing the thermoelectric performance through utilizing symmetry and asymmetry in thermoelectrics.