A method for manufacturing a thin layer of absorbing material consisting substantially of one or more sulfides and selenides of Cu, Zn and Sn, with the atomic percentages of the three materials Cu, Zn and Sn being able to vary in the interval from x=40 to 60% for Cu and y= 15 to 35% for Zn and z= 15 to 35% for Sn, with x+y+z=100%, with an atomic percentage of Se by replacing S being able to vary in the interval from 5% to 100%, in the form of a pentanary compound Cu-Zn-Sn-S-Se, hereinafter designated as a CZTSSe compound, with large crystal grains having an average size of at least 700 nm, said thin layer of absorber being deposited on one or more materials in one or more layers forming a substrate, wherein the following successive steps are performed: 1) a layer is deposited using a dispersion of particles, in liquid form, said particles being nanoparticles of one or more Cu, Zn and Sn sulfides, containing nanoparticles of quaternary compounds Cu-Zn-Sn-S having a content of quaternary compounds of at least 70%, the remainder consisting of binary nanoparticles M-S or ternary nanoparticles M-M'-S, M and M' being Cu, Zn or Sn, on a molybdenum (Mo) layer of a said substrate covered with a layer of molybdenum (Mo), and 2) an annealing heat treatment of said layer deposited on said substrate is performed at a maximum temperature of at least 450°C, in order to obtain crystallisation and growth of the nanoparticles, characterised in that: - in step 1), a layer is deposited using a colloidal hydroalcoholic dispersion of particles, said particles comprising primary nanoparticles of quaternary compounds CZTS of one or more Cu, Zn and Sn sulfides of sizes less than 100 nm, wherein the agglomerates of primary nanoparticles of agglomerate sizes greater than 5 μm, deposited at atmospheric pressure, in liquid form by spraying or by immersion have been removed, and - in step 2), said heat treatment comprises two annealing steps in different atmospheres following successively, in order to obtain large crystal grains with average size of at least 700 nm, on a thickness of 1 to 5 μm, namely: - a first annealing step in an inert gas atmosphere, and - a second annealing step in an inert gas atmosphere containing Se vapours. 1) a layer is deposited using a dispersion of particles, in liquid form, said particles being nanoparticles of one or more Cu, Zn and Sn sulfides, containing nanoparticles of quaternary compounds Cu-Zn-Sn-S having a content of quaternary compounds of at least 70%, the remainder consisting of binary nanoparticles M-S or ternary nanoparticles M-M'-S, M and M' being Cu, Zn or Sn, on a molybdenum (Mo) layer of a said substrate covered with a layer of molybdenum (Mo), and 2) an annealing heat treatment of said layer deposited on said substrate is performed at a maximum temperature of at least 450°C, in order to obtain crystallisation and growth of the nanoparticles, characterised in that: - in step 1), a layer is deposited using a colloidal hydroalcoholic dispersion of particles, said particles comprising primary nanoparticles of quaternary compounds CZTS of one or more Cu, Zn and Sn sulfides of sizes less than 100 nm, wherein the agglomerates of primary nanoparticles of agglomerate sizes greater than 5 μm, deposited at atmospheric pressure, in liquid form by spraying or by immersion have been removed, and - in step 2), said heat treatment comprises two annealing steps in different atmospheres following successively, in order to obtain large crystal grains with average size of at least 700 nm, on a thickness of 1 to 5 μm, namely: - a first annealing step in an inert gas atmosphere, and - a second annealing step in an inert gas atmosphere containing Se vapours. - in step 1), a layer is deposited using a colloidal hydroalcoholic dispersion of particles, said particles comprising primary nanoparticles of quaternary compounds CZTS of one or more Cu, Zn and Sn sulfides of sizes less than 100 nm, wherein the agglomerates of primary nanoparticles of agglomerate sizes greater than 5 μm, deposited at atmospheric pressure, in liquid form by spraying or by immersion have been removed, and - in step 2), said heat treatment comprises two annealing steps in different atmospheres following successively, in order to obtain large crystal grains with average size of at least 700 nm, on a thickness of 1 to 5 μm, namely: - a first annealing step in an inert gas atmosphere, and - a second annealing step in an inert gas atmosphere containing Se vapours.