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Abstract
This work starts with the synthesis of relatively thick n-type CuInS2 film by a single-step electrodeposition followed by calcination in a mixture of N2 and H2 at 500 ºC without the need of toxic H2S gas for sulfurization. It was found that the heat treatment in reducing atmosphere suppresses the formation of oxide impurity of the electrodeposited Cu/In/S elements and increases the donor density of CuInS2 by increasing the sulfur vacancies at the grain surface. The resultant CuInS2 film from reducing gas calcination exhibited a fourfold enhancement in photoelectrochemical performance as compared to that from calcination in pure N2.
Following the synthesis of the n-type CuInS2 film, a one-dimensional (1-D) CuInS2-ZnO composite was designed to improve the electron transport within the photoanode and capture the visible-light absorption for photoelectrochemical applications. Well-aligned ZnO nanorods were successfully coated with a uniform thin layer of CuInS2 nanoparticle photosensitizers using a tailored sequential pulsed-electrodeposition. The formation of CuInS2-ZnO heterojunction with well-matched band energy alignment and the superior electron mobility in ZnO nanorods led to remarkable improved photoelectrochemical performance of the electrode under visible light irradiation. The effects of deposition sequences and pulsing frequency in the sequential pulsed electrodeposition were found to be crucial in the photoelectrochemical properties of these photoelectrodes.
Besides the ternary sulphide CuInS2, binary sulphide such as CdS was also studied for the application of photoelectrodes due to its advanced visible light activity. The last part of the thesis focuses on the development of one-dimensional CdS-ZnO composites prepared by pulsed electrodeposition with specific synthesis conditions. An ultrathin CdS film with a thickness less than 10 nm was formed on the pre-grown ZnO nanorod arrays. The CdS-ZnO heterojunction electrode yielded a significant improvement in the photoelectrochemical properties comparing to pure CdS and pristine ZnO nanorod arrays films. The application of pulsed electrodeposition in this work will provide a new platform into the development of decorating 1-D structure with various metal sulphide materials.