Due to the increasing scarcity of fossil fuels and the growing demand for energy, it has become necessary to research new renewable energy sources for high-performance organic photovoltaic materials. In this context, a series of new donor–acceptor–donor compounds, based on the thieno[3,4-b]pyrazine core unit, have been designed and theoretically investigated. Donor moieties were introduced to design novel derivatives aimed at enhancing both optical absorption and charge transport properties, denoted respectively as: PTH, PTH4PF, PTH4POME, and PTHCBZ. The geometric, electronic, optical and photovoltaic characteristics of these molecular structures have been studied in depth through extensive theoretical studies. Exhibited energy gap (EH-L =EHOMO - ELUMO) ranging from 2.48 to 2.32 eV, with absorption wavelengths (λabs) between 552 and 589 nm. The Voc obtained values ranged from 0.77 to 0.99 V, while the LHE values varied between 0.59 and 0.87. This study highlights the impact of structural modifications on the electronic and photovoltaic properties of organic molecules, providing valuable guidance for the experimental design of high-efficiency organic solar cells.