This manuscript represents the theoretical study of new organic candidate materials based on thiophene and oxathiazole for applications in the field of organic solar cells (BHJ type) or dye-sensitized solar cells (DSSC type). We were first interested in the structural and electronic study of these organic materials using different methods of quantum chemistry. For this purpose, modulations of the electronic and optical properties of new structures were carried out by chemical modification of the conjugated chain either by substitutions or by modifying the nature of the donor (D), the acceptor (A) and/or the length of the ¿-conjugate system. The novelty of this work lies in the fact that these key parameters, which control optoelectronic and photovoltaic properties, have made it possible to propose new organic materials with diversified structures for photovoltaic applications.