Spray pyrolysis of chalcopyrite thin films

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Chalcopyrite CuInS_2 thin film is one of the most important material as absorbers of solar cells. We studied spray pyrolysis of the CuInS_2 thin films which used solutions containing Cu-In-and S-compounds. This process is known as a low-cost process of thin films. In this research we made a supersonic spray pyrolysis system and studied CuInS_2 thin films in their composition and surface morphology.First, we tried to use a mixed solution containing Cu-,In-,and S-sources. The above solution, however, tend to form white precipitates, which is not suitable for a spray deposition. We thus tried the following three processes.1)We deposited by spraying Cu-and In-sources to form Cu-In metallic film. Afterward, we sulfurized it by H_2S gas to from CuInS_2 thin films.2)Cu-In metallic film was evaporated from elemental Cu and In. Later, a solution containing CH_3CSNH_2 was sprayed to sulfurize a CuInS_2 thin film.3)Two spray depositions of Cu-In metallic film and a CH_3CSNH_2 solution were successively made to form a CuInS_2 thin film.We could make CuInS_2 thin films by 1-3) processes. The grown CuInS_2 films, however, consist of fiber-like compounds, which are quite different from those gown by a vacuum evaporation and H_2S sulfurization. Moreover, x-ray diffraction spectra from sprayed film show the existence of Cu oxide as well as Cu sulfide, which are not removed by KCN treatment. We, thus, have to remove those Cu compounds to apply this film for solar cells.