NOVELTY - The method for producing a light-sensitive thin-film structure for a photocathode, which is used for catalytic hydrogen development, comprises homoepitaxially growing a crystalline p-doped indium phosphide layer with (100):(2x 4)-reconstructed surface containing more indium than phosphorus on p-doped (100)-indium phosphide wafer in a preparation step, and electrochemically activating the surface of the indium phosphide layer in chloride-containing acid under the exposure with white light at room temperature with production of an interfacial film made of indium oxide in a light-induced manner.    USE - The method is useful for producing a light-sensitive thin-film structure for a photocathode, which is used for catalytic hydrogen development, where the hydrogen is used in combustion engine.    ADVANTAGE - The method ensures efficient and economical production of the light-sensitive thin-film structure with long term stability.    DETAILED DESCRIPTION - The method for producing a light-sensitive thin-film structure for a photocathode, which is used for catalytic hydrogen development, comprises homoepitaxially growing a crystalline p-doped indium phosphide layer with (100):(2x 4)-reconstructed surface containing more indium than phosphorus on a p-doped (100)-indium phosphide wafer in a preparation step, electrochemically activating the surface of the indium phosphide layer in a chloride-containing acid under the exposure with white light at room temperature with a production of an interfacial film made of indium oxide in a light-induced manner and by performing cyclic voltammetry between an open circuit voltage and a cathodic turning-point potential, during which the inversion in the indium phosphide layer occurs in a conditioning step, where a number of cycles is passed up to the saturation of the cathodic photo-current in cathodic turning-point potential, depositing a catalytic active layer made of nanoparticles of a transition metal from a conductive electrolyte solution electrolessly or under constant voltage and under exposure with a photon energy above an absorption edge of indium phosphide at room temperature with a thickening of the interfacial film and an additional binding of phosphorus oxide and phosphates in a light-induced manner in a deposition step, where the catalytic active layer completely covers the interfacial film, removing or splitting the prepared indium phosphide layer after the preparation step or the thin-film structure from the indium phosphide wafer after the deposition step in a separation step, and reusing the indium phosphide layer in the preparation step. The preparation step comprises introducing the indium phosphide wafer with a thickness of 50-500 mu m and/or a p-dopant with zinc, homoepitaxially growing the indium phosphide layer with a thickness of 3-5 mu m by metal-organic vapor phase epitaxy from the precursor compounds of trimethylindium and tertiarybutylphosphine, p-doping the indium phosphide layer with zinc from the precursor compound of diethyl zinc in a lesser concentration than the concentration of the indium phosphide wafer, and heating the surface of the indium phosphide layer at 500-650 degrees C during the homoepitaxial growth. The conditioning step comprises performing the cyclic voltammetry in constant steps in a range of 5-100 mV/s, performing the cyclic voltammetry between +0.3 V to -0.1 V, introducing hydrochloric acid or perchloric acid with a pH-value of 0-3 as acid solution, and exposing with a photon energy of 50-200 mW/cm2. The deposition step comprises introducing rhodium, platinum, iridium, cobalt, chromium, manganese, nickel, molybdenum and/or iron as transition metal, introducing the transition metal as dissolved transition metal salt in a dissolved 5 mM chloride compound in an aqueous 0.5 M sodium chloride solution, which is displaced with 5 vol.% of isopropanol, as conductive electrolyte solution, applying a voltage of -0.2 V to the indium phosphide layer, exposing with a photon energy of 50-200 mW/cm2, and depositing over a time period of 10-20 seconds. The layer thickness of the indium phosphide layer is 3-5 mu m, the layer thickness of the interfacial film is 4-7 nm, and the layer thickness of the catalytic active layer is 5-25 nm where the significant height variations occur, with a diameter of the nanoparticles is 2-10 nm.    DESCRIPTION OF DRAWING(S) - The figure shows a tapping mode atomic force microscopy image of a surface of an indium phosphide layer.