High Thermoelectric Figure of Merit via Tunable Valley Convergence Coupled Low Thermal Conductivity in A^IIB^IVC₂^V Chalcopyrites

Developing high performance thermoelectrics require designing strategy to obtain excellent electronic but poor phononic transport properties. Tetragonal chalcopyrites are of significant attention due to complex electronic structures affecting the transport properties. Conflicting requirements of achieving high Seebeck coefficient and electrical conductivity are simultaneously reached, by tuning crystal and electronic structures by isoelectronic substitution, leading to unprecedented enhancement in electronic transport properties of A^IIB^IVC₂^V (II = Be, Mg, Zn, and Cd; IV = Si, Ge, and Sn; and V = P and As). Existing multiple valleys in conduction bands get converged by substitution of group IV dopants to offer enhanced powerfactors for n-type carriers. These substitutions improve convergence of valence bands having a direct correlation with tetragonal distortion (η) of these chalcopyrites. For small distortion in system (η~1), complete convergence of bands is achieved, enhancing the p-type powerfactor. Excellent electronic transport and low thermal conductivity results in maximum ZT of 1.67 in CdGeAs₂ for n-type doping. The approach developed to enhance the thermoelectric efficiency can be useful to design new thermoelectric materials.
J. Phys. Chem. C 2018, 122, 29150−29157