There is today an intense search for new electron donor polymers for active layers of organic solar cells. One approach currently employed to obtain new polymers with more interesting electronic properties is the synthesis of copolymers in which there is a mix of electron donor monomers with others who are electron acceptors. Usually the comonomers have very different structure. In this work we show that the approach of using similar comonomers can provide changes in the frontier electronic levels showing a good compromise between all the desired properties. Employing a DFT/B3LYP/6-31G(d) methodology, we explore the properties of copolymers consisting of comonomers of poly(3-hexylthiophene) (P3HT), poly(3-hexyloxythiophene) (P3HOT) and some poly(3-hexylthiophene) derivatives. The results indicate that the copolymers now have intermediate frontier orbital energies when compared to the parent homopolymers and we will show that it is possible to anticipate the values of the same energy levels of the copolymer with any number of each comonomer. This approach is an alternative way to design a copolymer with a favorable tuning of the energies of the frontier electronic levels and is supported by experimental evidence.