8. Conclusion

which indicates substitutional doping in ZnO samples. In this work, the crystallite size was calculated using the Scherrer method which is considered as a standard method. The Scherrer method has revealed that the crystallite size increases as the dopant levels increase. The calculated crystallite sizes for both un-doped and C-ZnO were 9.60, 9.99, 0.96 and 10.22 nm for un-doped ZnO, 0.01 M C-ZnO, 0.015 M C:

Figure 13 shows the UV-Vis diffuse reflectance spectra (DRS) of the synthesized un-doped and C-doped ZnO NPs. The UV-Vis DRS analysis has shown that there is a shift in absorption edge as the dopant level increases. The energy band gaps of the ZnO NPs were estimated by using Eg = 1239/λEdge\*eV. The absorption

ZnO and 0.025 M C:ZnO samples, respectively.

XRD patterns of ZnO NPs synthesized by PSP technique.

Zinc Oxide Based Nano Materials and Devices

Figure 12.

Figure 13.

92

7.4 Diffuse reflectance spectroscopy (DRS)

The DRS spectra of the unmodified and C-ZnO samples synthesized by PSP system.

Gathering knowledge about the challenges that other researchers experienced when working with spray pyrolysis for the production of ZnO together with understanding the properties and the crystal structure of ZnO has made it possible to design a novel pneumatic spray pyrolysis (PSP) system from ultrasonic spray pyrolysis (USP) for the deposition of ZnO NPs. The novel PSP system developed has presented unique features in material synthesis of ZnO nanostructures, like using the horizontal furnace reactor as compared to the vertical systems used in other techniques such as CVD, sol-gel, ion-assisted deposition etc. The horizontal system offers several advantages for thin film deposition in the absence of any tailing effect detected in the partial or oblique angle illustrations like in almost all the CVD methods. The samples in this system were deposited at 90° angle, which enables the aerosol beam comprised of the precursor solution vapor to directly cooperate with the substrate consistently. This system was able to produce the desired ZnO nanostructured properties for solar cell application. The SEM micrographs of both un-doped and carbon-doped samples have revealed the formation of spherical-shaped ZnO nanoparticles mesoporous morphology. The SEM images also revealed that the morphology and shape of the fabricated ZnO samples change as the dopant level increases. Additionally, the EDX analysis has confirmed the presence of Zn, C and O in the synthesized samples which indicates the successful pyrolysis of zinc ethoxide solution to form ZnO nanoparticles. The cross-sectional SEM has revealed the increase in film thickness as the dopant levels increase from 0.31 to 0.41 μm. The XRD has revealed the characteristic peaks of the hexagonal Wurtzite structure of ZnO for both un-doped and carbon-doped ZnO samples. XRD lines were observed at 31.90, 34.50, 36.34, 47.73, 56.88, 63.04, 68.20 and 77.33° and were indexed as (100), (002), (101), (102), (110), (103), (200) and (112), respectively. Additionally, the XRD analysis has also revealed a shift in the peaks to higher 2θ standards, which indicates the substitutional doping in the synthesized carbon-doped samples. Lastly, the UV-Vis DRS analysis has revealed a blue shift in absorption spectra of the synthesized samples with an increase in carbon doping.
