Spray pyrolysis method has been widely applied to a variety of thin films. Several researches have investigated the mechanism of spray pyrolysis deposition (SPD). However, those models concern the influence of deposition temperature and initial droplet size. There was a noticeable absence of research projects dealing with the role of precursor solutions in SPD system. In this study, a conceptual model for spray pyrolysis mechanism is presented. The falling process of a precursor droplet from the nozzle to the substrate is divided into five steps: the ironic components in the precursor solution, the solvents used in the precursor solution and their vaporization, the precipitation of the precursor solution, the vaporization of the precipitation, and the pyrolysis of the precipitation. They can be further cataloged into two segments: solution precipitation and CVD process. The model is experimentally supported by deposit amorphous alumina thin film on silicon wafer. At a constant substrate temperature, 440℃, the films were deposited by various deposition solutions. AlCl3 and Al(acac)3 were used as precursor solute, and the solvents are deionized water, methanol, and ethanol. Acetylacetone and hydrochloric acid were the additives in the solution. The resultant thin films have shown good passivation ability, which can be further applied on the passivation layer for c-Si solar cell.

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