Ultrahigh Thermoelectric Performance of ZnO-CdO Thin Films

Abstract

Zinc oxide (ZnO) is emerging as a promising n-type thermoelectric material (TE) for power harvesting due to its high melting point and large Seebeck coefficient. However, the TE performance of ZnO is limited by high thermal conductivity and low carrier mobility. Adding or doping a divalent element such as cadmium oxide (CdO) can lower the thermal conductivity and enhance the carrier concentration of ZnO. In this paper, the thermoelectric transport properties of ZnO-CdO nanocrystalline thin films are investigated by varying the Zn/Cd ratio at temperatures ranging from room temperature (RT) to 423 K. The electrical conductivity, carrier concentration and mobility of ZnO were enhanced by increasing the Cd concentration. The maximum power factor of 2.75 × 10−4 W m−1 K−2 was obtained at 423 K for the Zn/Cd = 1:3 sample. The thermal conductivity was dominated by lattice thermal conductivity in which Umklapp scattering occurs between anharmonic phonons. The thermal conductivity of ZnO decreased significantly with increasing Cd concentration. The highest estimated figure of merit (ZT) of 0.59 was found at 413 K for the Zn/Cd = 1:3 sample, which is 223 times greater than for ZnO, indicating that the film is efficient in energy generation.