Electrospray Deposition of Functional Thin Films ? Fabrication and Characterization

Abstract

Electrospray deposition (ESD) process is capable of spraying and depositing various substances such as organic/inorganic compounds and/or synthetic polymers. ESD process can maintain the sample relatively free from damage, since the whole procedure is conducted under room temperature and atmospheric pressure. Fabrication of nano-sized particles and fibers and deposition in a large area are possible. This is the first account where ESD is being utilized for different functional materials? deposition, and the films are characterized thoroughly taking ESD in competition to the existing thin film deposition techniques like chemical vapour deposition, plasma related techniques and physical vapour deposition techniques. Although many scientists and researchers have adopted ESD as their research topic, ESD has been only utilized in mass spectroscopy and powder production applications. In this thesis three different types of thin films are deposited via ESD and characterized thoroughly making them perfectly suitable for their use in device fabrication. First Copper Indium diSelenide (CIS) ,which is a direct bandgap semiconductor useful for manufacturing solar cells is deposited. CIS nano-particles, manufactured through solvo-thermal process are dissolved in Ethanol:Terpineol solution, and six different types of inks are prepared on the basis of different solvent composition and particle concentration. Fabricated layers are characterized for their purity, morphology, optical, structural and electrical properties, and an optimum ink is identified. In the second phase of the thesis, Zinc Oxide (ZnO), which is a wide-bandgap n-type semiconductor of the II-VI semiconductor group, thin films are fabricated via ESD. ZnO nano particle ink is first prepared by dissolving the nanoparticles in Ethanol, and Triton is used as a surfactant. The ink is then subjected to ESD to fabricate ~120 nm thick films which are characterized for their surface morphology, phase, purity and optical & electrical properties thereby elucidating ESD as a cheap and easy alternative to the conventional thin film deposition processes. In the last part of this study, transparent conductive oxide films i.e. Aluminum doped Zinc Oxide (ZnO:Al) films are fabricated and characterized in the same way as ZnO films. The fabricated films in this thesis compete with the ones made by different intricate and expensive conventional systems. The main advantage is that ESD process precludes the use of high vacuum systems therefore making the process cheap and simple. Also material wastage is very small, and inks used in the process are completely inert to the environment thereby making the process and clean and green.