The invention relates to a method for production of thin layers of semiconductor alloys of the I-III-VI2 type, including sulphur, for photovoltaic applications, whereby a heterostructure is firstly deposited on a substrate comprising a thin layer of precursor I-III-VI2 which is essentially amorphous and a thin layer, including at least some sulphur, the heterostructure is then annealed to promote the diffusion of the sulphur into the precursor layer and the at least partial crystallization of the I-III-VI2 alloy of the precursor layer with a stoichiometry which hence includes sulphur. A layer of selenium may also be deposited to assist the recrystallization processes or annealing.