Thermoelectric materials: Energy conversion between heat and electricity

Thermoelectric materials have drawn vast attentions for centuries, because thermoelectric effects enable direct conversion between thermal and electrical energy, thus providing an alternative for power generation and refrigeration. This review summarizes the thermoelectric phenomena, applications and parameter relationships. The approaches used for thermoelectric performance enhancement are outlined, including: modifications of electronic band structures and band convergence to enhance Seebeck coefficients; nanostructuring and all-scale hierarchical architecturing to reduce the lattice thermal conductivity. Several promising thermoelectric materials with intrinsically low thermal conductivities are introduced. The low thermal conductivities may arise from large molecular weights, complex crystal structures, liquid like transports or high anharmonicity of chemical bonds. At the end, a discussion of future possible strategies is proposed, aiming at further thermoelectric performance enhancements.