Thermoelectric properties of four different ZnO nanostructures*

In this work, we studied the thermoelectric properties of four different ZnO morphologies, namely, nanoribbons, nanorods, nanoparticles, and nanoshuttles. Experiments were performed from 324K to 364 K. Temperature-dependent Seebeck coefficients were observed by using Seebeck controller techniques. Electrical conductivity was measured by the Vander Pauw method. Seebeck coefficients for the four morphologies were negative which confirmed that all synthesized ZnO nanostructures are n-type semiconductors.  The absolute value of the Seebeck coefficients increased with increasing temperature. The electrical conductivity of ZnO morphologies also shows an increasing trend with temperature. Seebeck coefficients did not significantly change with different  ZnO morphologies. However, electrical conductivity showed a significant variation with ZnO morphology. The highest electrical conductivity (1080 Ω  ^-1m^-1) and electronic thermal conductivity (9.86 × 10^-3W/mK) were obtained in ZnO nanorods at 364K, whereas   ZnO nanoshuttles showed the lowest electrical conductivity (0.30 Ω  ^-1m^-1) and electronic thermal conductivity (1.48 × 10^-6 W/mK) at 324K. The maximum Power factor was obtained in ZnO nanorods at all temperatures compared to other morphologies. Our studies indicate that ZnO nanorods have the highest thermoelectric properties compared to other ZnO nano morphologies.