A method for a preparation of a semiconducting film of an organic-inorganic metal-halide compound with a perovskite-like structure, comprising the following steps a) applying a layer of a precursor of a component B on a substrate, b) applying a layer of a composite reagent onto the surface of the precursor layer of component B, and c) treatment of the applied layers on the substrate by the reagent X 2 during the time which is necessary and sufficient for completion of a chemical reaction of the applied composite reagent and the precursor of component B resulting in an organic-inorganic metal-halide perovskite-like compound formation, characterizing in that the composite reagent applied in the step b) contains a mixture of AX and X 2 reagents with a [X 2]/ molar ratio in the range 0 < [X 2] / <1, and the film obtained after the step b) contains the seeds of the phase with a perovskite-like structure, wherein the component B contains cations M n+ of different metals selected from Pb, Sn, Bi, as well as mixtures thereof, the reagent AX is a salt comprising cation A + and anion X -, wherein the cation A + is a singly charged organic or inorganic cation selected from methylammonium CH 3 NH 3 +, formamidinium (NH 2) 2 CH +, guanidinium C(NH 2) 3 +, Cs +, Rb + and unsubstituted (NH 4 +) or substituted ammonium cations including monosubstituted or disubstituted or trisubstituted or tetrasubstituted ammonium cations, as well as combination thereof; and the anion X - is a singly charged anion selected from Cl -, Br -, I - or a pseudo-halide anion, as well as combination thereof, the reagent X 2 is a molecular halogen. a) applying a layer of a precursor of a component B on a substrate, b) applying a layer of a composite reagent onto the surface of the precursor layer of component B, and c) treatment of the applied layers on the substrate by the reagent X 2 during the time which is necessary and sufficient for completion of a chemical reaction of the applied composite reagent and the precursor of component B resulting in an organic-inorganic metal-halide perovskite-like compound formation, characterizing in that the composite reagent applied in the step b) contains a mixture of AX and X 2 reagents with a [X 2]/ molar ratio in the range 0 < [X 2] / <1, and the film obtained after the step b) contains the seeds of the phase with a perovskite-like structure, wherein the component B contains cations M n+ of different metals selected from Pb, Sn, Bi, as well as mixtures thereof, the reagent AX is a salt comprising cation A + and anion X -, wherein the cation A + is a singly charged organic or inorganic cation selected from methylammonium CH 3 NH 3 +, formamidinium (NH 2) 2 CH +, guanidinium C(NH 2) 3 +, Cs +, Rb + and unsubstituted (NH 4 +) or substituted ammonium cations including monosubstituted or disubstituted or trisubstituted or tetrasubstituted ammonium cations, as well as combination thereof; and the anion X - is a singly charged anion selected from Cl -, Br -, I - or a pseudo-halide anion, as well as combination thereof, the reagent X 2 is a molecular halogen. the reagent AX is a salt comprising cation A + and anion X -, wherein the cation A + is a singly charged organic or inorganic cation selected from methylammonium CH 3 NH 3 +, formamidinium (NH 2) 2 CH +, guanidinium C(NH 2) 3 +, Cs +, Rb + and unsubstituted (NH 4 +) or substituted ammonium cations including monosubstituted or disubstituted or trisubstituted or tetrasubstituted ammonium cations, as well as combination thereof; and the anion X - is a singly charged anion selected from Cl -, Br -, I - or a pseudo-halide anion, as well as combination thereof, the reagent X 2 is a molecular halogen.