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CuInS 2 films were deposited by spray pyrolysis method at 250 °C and 350 °C using aqueous solutions of CuCl 2 , InCl 3 and SC(NH 2 ) 2 at molar ratio of precursors Cu:In:S=1:1:3 in spray solution. Films were characterized by X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS) techniques. According to XPS, the films grown at 350 °C have Cu 2+ containing pieces on the surface, the film composition in bulk region is not homogeneous and contains metal bonded oxygen in amount of 5-8 at.%. Deposition at 250 °C reduces the content of oxygen down to ∼ 1 at. %, the films are low-crystalline with uniform distribution of the elements throughout the film and contain some excess of sulfur compared to stoichiometric CuInS 2 .

Structural, electrical and optical properties of CuInS2 thin films of various thicknesses, grown on heated glass substrates at 100 °C by thermal evaporation method were studied. These films were annealed in air atmosphere at temperature of 200 °C. The thickness of the CIS films was varied from 436 to 80 nm. It was found that the structural properties, FWHM and grain size degraded with decreasing its thickness. The peak intensity decreases with the film thickness and the X-ray spectra are polycrystalline in nature excluding films with thickness less than 111 nm, the peak intensity disappears and films are amorphous in nature. However, with decreasing the film thickness from 436 to 111 nm, the optical band (Eg) gap of CuInS2 material is in the range 1.42 to 1.81 eV. Hot probe method showed that all the annealed CuInS2 samples exhibit n-type conductivity with low resistivity values in the range 3.60 to 0.08 kΩ.m. We suggests that the minimum thickness to obtain polycrystalline CuInS2 thin films is 111 nm, the band gap energy of CuInS2 thin films can be controlled by varying the film thickness and the n-type conductivity can be obtained after annealing in air atmosphere.

ZnO thin films in nanorod (NR) and nanoflower (NF) morphologies were used as photoelectrode scaffolds for efficient visible-light-driven photoelectrochemical (PEC) water splitting process, where their decoration with copper indium gallium sulfide (CIGS) and indium sulfide (In2S3) layers resulted in significant PEC performance enhancement. ZnO NF/CIGS/In2S3 photoelectrodes exhibited a remarkably high PEC efficiency (similar to 6.0% applied bias photon-to-current efficiency, 83% incident photon-to-current efficiency) due to the negligible dark current, while ZnO NR/CIGS/In2S3 generated a photocurrent density of 30.0 mA.cm(-2) at 0.4 V (vs Ag/AgCl), being one of the highest performances reported in the literature for copper-based chalcopyrite photoelectrodes so far. The interfacial photoelectrode-electrolyte charge transport dynamics, investigated via intensity-modulated photocurrent spectroscopy, exhibited a sevenfold increase in charge transfer efficiencies with a significant drop in surface recombination kinetics for ZnO NF after CIGS/In2S3 decoration. The obtained results show consistency with numerically modeled electric field distribution profiles and electron paramagnetic resonance results of ZnO NF, rationalizing the enhanced charge transfer rates for decorated samples and confirming the defect passivating nature of CIGS/In2S3.

Though Cu2O has demonstrated high performance as a photocathode for solar water splitting, its band gap is too large for efficient use as the bottom cell in tandem configurations. Accordingly, copper chalcopyrites have recently attracted much attention for solar water splitting due to their smaller and tunable band gaps. However, their fabrication is mainly based on vacuum evaporation, which is an expensive and energy consuming process. Here, we have developed a novel and low-cost solution fabrication method, and CuInS2 was chosen as a model material due to its smaller band gap compared to Cu2O and relatively simple composition. The nanostructured CuInS2 electrodes were synthesized at low temperature in crystalline form by solvothermal treatment of electrochemically deposited Cu2O films. Following the coating of overlayers and decoration with Pt catalyst, the as-fabricated CuInS2 electrode demonstrated water splitting photocurrents of 3.5 mA cm(2) under simulated solar illumination. To the best of our knowledge, this is the highest performance yet reported for a solution-processed copper chalcopyrite electrode for solar water splitting. Furthermore, the electrode showed good stability and had a broad incident photon-to-current efficiency (IPCE) response to wavelengths beyond 800 nm, consistent with the smaller bandgap of this material.