Currently, there is an intensive search for new materials to make more efficient organic solar cells. The use of chemical modifications capable of modifying the electronic properties of materials already known is an interesting approach, as it can, in principle, provide a more adequate adjustment of the frontier electronic levels while preserving properties such as solubility. Thus, employing a DFT/B3LYP/6-31G(d) methodology, we performed a theoretical study of the polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7) and 13 new derivatives obtained by substitution with electron acceptor and donor groups in order to understand how the energy levels of the frontier orbitals are modified. For that, besides of studying the PTB7 without modifications, we substitute the hidrogens atoms of the benzodithiophene (BDT) moiety of the PTB7 by the following atoms: chlorine, bromine, fluorine, hydroxy, cyano, amino, methyltio, trifluoromethyl, methyl, dimethylamino, metoxy, carboxy, and ethenyl. The results yielded new materials with modified frontier orbital energies and it is possible to observe a dependence of the electronic properties as a function of the modified atom position or substituent's acceptor/donor character.