Development of Advanced Thin Film Photovoltaic Device using Chalcopyrite Semiconductor

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It is an important issue to develop a low cost and high efficient solar cel1 in order to make photovoltaic system put in practical use. In this research, the solar cel1 with chalcopyrite semiconductor as an activity layer was investigated. This semiconductor is expectable to provide a low cost device because the optical absorption coefficient is large, and a high efficient device because the band gap is adjustable to the theoretical optimal value. In this research, the purpose is to develop a next-generation thin film solar cell with low cost and high efficiency. Cu(In, Ga) (S, Se)_2 thin films were produced by crystallizing In/CuIn(Ga)Se precursor on Mo/soda lime glass substrate in Se and S mixing atmosphere. Moreover, Cu(In, Ga)Se_2 thin films were produced by thermal treatment of stacked CuInSe/CuGaSe precursor in Se atmosphere. By using this method, the crystallized thin films, which have a chalcopyrite structure and can regulate their composition and band gap, were obtained. The effects of the solution concentration and the annealing after the formation of CdS thin films by chemical bath deposition from iodine compounds were evaluated by the crystallinity, the electrical property and the optical characteristic. Especially, the solar cell performance was rapidly improved by the annealing after formation. The influence of the oxygen introduction effect and the substrate position were evaluated for i-ZnO thin films prepared by sputtering. It was effective to have introduced oxygen into the sputtering gas for a higher resistivity. The annealing of n-ZnO prepared by rf magnetron sputtering with off-axis configuration was carried out to reduce the resistivity. Its value decreased with increasing the annealing temperature. The solar celIs were produced and the change of the efficiency etc. was investigated. The rapid improvement in the open circuit voltage of a solar cell was confirmed by crystallizing in Se atmosphere which added S.