Studies On The Ternary Chalcogenide Semiconductor Thin Films Prepared From Soft Solution Processing

ETA solar cell with chalcogenide semiconductors as extremely thin absorber layer is one of the promising devices in solar energy. There has been considerable interest for developing CuInS₂ and CuInSe₂ thin film using low temperature chemical methods such as CBD, SILAR and electro-deposition. Advantage of these processes is that they are pollution free, low cost and soft solution processing. This dissertation begins with an overview of solar cells and sulphide thin film. Based on the background, the preparation of CuInS₂ and CuInSe₂ by such methods were researched and .the characterization of the films was carried out by XRD,SEM,XPS and Hall system.By CBD process, CuInS₂ films were prepared from aqueous bath containing CuCl₂, InCl₃, TEA and CS(NH₂)₂. In 8～1₂h of deposition, the films exhibited uniform and compact morphology. After annealed at 500℃for 1h, the films were improved in stoichiometry and showed a chalcopyrite structure. The absorption coefficients of CuInS₂ films were more than 104 cm-1 and the band gap was 1.42 eV.Relatively simple, quick, less waste and economical, SILAR method is based on the immersion of substrates in separate cationic and anionic precursors. Yet, by now literature surveys show that there is no attempt to prepare ternary metal sulphide thin film using SILAR method. In this dissertation, preparations and properties of chalcopyrite CuInS₂ and CuInSe₂ thin films on glass substrate were firstly reported. Characterization of CuInS₂ films deposited on porous TiO₂ substrate was also investigated. XPS results showed CuInS₂ and CuInSe₂ films with near stoichiometry were derived from [Cu]/[In]=1.25 and 1.5 respectively in mixing cation precursor solution. Annealing process was effective for improving the crystalline structure and surface uniformity of the as-grown film. Optimum annealing temperature for CuInS₂ and CuInSe₂ thin film was 450℃and 400℃respectively. Their resistivity decreased with annealing temperature, while the absorption coefficients, carrier concentration and mobility increased. Deposited CuInS₂ films on porous TiO₂ substrates, absorption coefficients and crystalline quality had all been improved due to the surface effects of nanometer porous material. The band gap values in range of 1.37 to 1.44eV indicated that CuInS₂ film on porous TiO₂ substrate had an excellent absorbability.CuInSe₂ thin film were grown on porous TiO₂ substrate by a one-step electro deposition process from the aqueous solution containing CuSO4,SeO₂,In₂(SO₄)₃ and citric acid. The scanning plots results showed that deposition potential of CuInSe₂ onporous TiO₂ substrate shifted from 750mv to -1250mV compared with that on glass substrate. XRD results demonstrated that -1100mv was the optimum deposition potential. Post-deposition annealing of the as-grown CuInSe₂ thin film helps a lot to gain a near stoichiometry film with better crystallinity and absorption coefficients. But the band gap decreased slightly after annealing process, which might be caused by the interface reaction between CuInSe₂ and TiO₂.