Diameter-dependent ultra-high thermoelectric performance of ZnO nanowires

Zinc oxide (ZnO) shows great potential in electronics, but its large intrinsic thermal conductivity limits its thermoelectric applications. In this work, we explore the significant carrier transport capacity and diameter-dependent thermoelectric characteristics of wurtzite-ZnO 〈0001〉 nanowires based on first-principles and molecular dynamics simulations. Under the synergistic effect of band degeneracy and weak phonon-electron scattering, P-type (ZnO)₇₃ nanowires achieve an ultra-high power factor above 1500 μW⋅cm⁻¹⋅K⁻² over a wide temperature range. The lattice thermal conductivity and carrier transport properties of ZnO nanowires exhibit a strong diameter size dependence. When the ZnO nanowire diameter exceeds 12.72 Å, the carrier transport properties increase significantly, while the thermal conductivity shows a slight increase with the diameter size, resulting in a ZT value of up to 6.4 at 700 K for P-type (ZnO)₇₃. For the first time, the size effect is also illustrated by introducing two geometrical configurations of the ZnO nanowires. This work theoretically depicts the size optimization strategy for the thermoelectric conversion of ZnO nanowires.