Polycrystalline CuInS2 chalcopyrite thin films were formed on a Mo-coated glass substrate by annealing of spray deposited precursor films in a sulfur atmosphere. Structural and photoelectrochemical analyses of CuInS2 films obtained by annealing at 500 °C and 600 °C revealed that a well-defined crystalline film was obtained by the 600 °C annealing. Owing to these favorable properties, the solar cell with an Al:ZnO/CdS/CIS/Mo/glass structure based on the 600 °C annealed CuInS2 film showed higher conversion efficiency than that obtained on the cell derived from the 500 °C annealed CuInS2. Partial incorporation of Ga in the CuInS2 film with a Ga/In ratio of ca. 0.2 to form a Cu(In,Ga)S2 mixed crystal without any reduction of photoelectrochemical properties can be achieved by introduction of a Ga source in the sprayed solution. As a result, the solar cell based on the 600 °C annealed Cu(In,Ga)S2 film showed the best conversion efficiency (5.8%) of the present sprayed chalcopyrite films. By introduction of a CdS thin layer followed by loading Pt deposits, moreover, the 600 °C annealed Cu(In,Ga)S2 film worked as a photocathode for photoelectrochemical water splitting with applied bias potential of >0.65 V.
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