Elucidating the role of lattice thermal conductivity in π-phases of IV-VI monochalcogenides for highly efficient thermoelectric performance

Recently, an emerging new class of cubic pi-polymorphs are being pursued as cost-effective and relatively less toxic materials for thermoelectric, photovoltaic, and optoelectronic applications. Using density functional formalism and semiclassical Boltzmann transport theory, we have systematically studied the thermoelectric performance of pi-polymorphs. Hybrid functional (HSE03) is employed to realize accurate energy bandgaps, which helps to predict more accurate thermoelectric properties. The thermodynamic stability is observed by binding energies and phonon dispersions. It is observed that the Seebeck coefficients (S) are decreasing and electrical conductivities (sigma) are increasing with carrier concentration. However, thermal conductivities are showing decreasing trends which lead to ultimately increased ZT. pi-GeSe shows a high power factor similar to 16.50 mW/mK(2) among all pi-polymorphs. The figure of merit, ZT value, of pi-SnS, pi-SnSe, pi-GeS, and pi-GeSe are found to be 0.83, 1.20, 1.28, and 1.63 with optimal carrier concentration at 800 K. The present work highlights the potential of newly discovered cubic pi-polymorphs of chalcogenides for highly efficient thermoelectric materials.