Solution-based Metal Oxide Passivation and Photoanode Layers for Photoelectrochemical Cells

Abstract

Photoelectrochemical (PEC) cells are attractive system to convert solar to chemical energy. Recently, development of photoelectrodes for enhance PEC have been reported with various semiconductor materials. To commercialize this system, the photoelectrode have to meet large scalable and low-cost in both bulk quantities and processes. Specially, silicon is considered a promising material for use as a photoanode because it has a low bandgap and can produce high efficiency in photoelectro water-splitting. However, silicon has a problem that it decomposes itself during an electrochemical reaction under an alkaline solution. Therefore, it is difficult to use it alone as photoanode. Therefore, silicon need to protecting layer. Currently, as a method of fabricating a material used as a layer to protect a silicon electrode, a process through ALD, CVD, etc. requiring an expensive high vacuum has been reported. This is because the passivation layer of silicon must be thin and sophisticated. In case of film made by solution process, high vacuum equipment is not required and cost can be reduced, but it is difficult to obtain thin thickness and precision In Chapter 2, we report the fabrication of a NiO/n-Si photoanode on a 4inch wafer scale. We investigated optimal conditions of NiO coating on n-Si for enhanced PEC properties. The 4 inch wafer scaled photoanode is successfully prepared by chemical bath deposition of nickel oxide film onto n-Si wafer with 3D structure. Compared to planer NiO/n-Si photoanode, the NiO/n-Si photoanode with 3D structure show improved PEC properties. These results could be useful for coating on photoanode with large surface area for enhancing PEC performance. In Chapter 3, we fabricate a thin and sophisticated nickel oxide passivation layer by adding a light irradiation pretreatment process that can overcome the disadvantages of the solution process in spite of being a film made by a solution process. We investigated optimal treatment conditions of nickel oxide layer on silicon photoanode for enhanced PEC properties. These results could be useful for using silicon as a photoanode for enhancing PEC performance. In Chapter 4, We investigated a hematite electrode with reduced surface resistance by adding a post-treatment process for light irradiation. As a result of light treatment, oxygen vacancy was created in hematite. We conducted a study to investigate the optimal treatment conditions for electrodes for improved PEC properties.