Thermal and electrical characterization of ZnO based pellets and thin films

The thermal and electrical properties of ZnO based pellets and thin films were studied by fabricated through inkjet printing method. Inkjet printing is a low cost alternative processing method for the fabrication of thin films. In this thesis, inkjet printing was used to fabricate thin films which were tested for their thermal and electrical properties. Thin film was successfully fabricated onto glass substrate using desktop inkjet printer. A minimum of 50 print cycles were required to obtain homogeneous films. The thickness of the inkjet printed Al-doped ZnO, ZnxFe2.04 and ZnxCUt-xFe2.04 thin films as obtained by SEM was approximately 9 J.Lm. The thickness of the films did not change with different composition. The thermoelectric properties of Al-doped ZnO, ZnxFe2.04 and ZnxCUtxFez04 pellets and thin films were improved with increasing dopant. The figure of merit for 4 wtO/o Al-doped ZnO fired at 800 °C was higher (Z- 0.58 xl 0-6) due to high electrical conductivity. Low thermal conductivity was obtained with increasing AI content. The figure of merit slightly decreased for 5 wt% Al-doped ZnO due to low electrical conductivity caused by the presence of the ZnAlz04 phase. The figure of merit for 4 wt% Al-doped ZnO thin films (Z- 0.13 x10-6) was lower compared to pellet (Z- 0.61 x10-6) due to the lower Seebeck coefficient in thin films. The figure of merit for ZnxFe20 4 pellets and thin films was improved by increasing Zn. The figure of merit for ZnxFe204 (x = 1.0) thin films (Z- 1.34 xl0-9 ) was lower compared to pellet (Z- 4.26 xlo-9) due to lower Seebeck coefficient in thin films. However, low thermal conductivity and high electrical conductivity of ZnxFez04 thin films was observed compared to pellet. The thermoelectric properties ofZnxCUt-xFez04 pellets and thin films were improved when increasing Zn due to its high Seebeck coefficient and low thermal conductivity. The figure of merit for ZnxCUt-xFe204 (x = 0.4) thin films (Z- 0.81 x1o-~ was lower compared to the pellets (Z - 3.06 x10-9) due to the low Seebeck coefficient in thin films. The thermoelectric properties Al-doped ZnO, ZnxFez04 and ZnxCUt-xFe204 were improved when fired in vacuum at lower temperature. The figure of merit for Al-doped ZnO (AI > 3 wt%) was decreased significantly when increasing sintering temperature due to the formation of ZnAlz04 phase at higher sintering temperature. The figure of merit for 4 wt% Al-doped ZnO fired at 800 oc in vacuum (Z- 0.61 xl0-6) was higher than samples fired in oxygen (Z-0.54 x 1 0-6) due to higher electrical conductivity when fired in vacuum. Higher figure of merit for ZnxFe204 (x = 1.0) was observed when fired in vacuum (Z - 4.37 x10-9) compared to samples fired in oxygen (Z- 4.26 x1o-~. The figure of merit for ZnxCu1_ xFez04 (x = 0.4) fired in vacuum (Z- 3.61 xl0-9) was higher than samples fired in oxygen (Z- 3.29 xl0-9). To summarize, thin films were obtained by printing out the solution on glass substrates. The thermoelectric properties of pellets were higher than the thin films. However, it must be noted that higher electrical conductivity was observed for thin films due to the smaller dimension in thin films. Slight changes in the thermal and electrical properties were observed when fired in different temperatures and atmospheres. The samples ftred in vacuum at lower temperature were observed with better thermoelectric properties due to higher magnitude of Seebeck coefficient.