Photosensitizers can impact on the efficiency of dye-sensitized solar cells (DYSCs) by adjusting their electromechanical and optical attributes, and because of this they are considered important. Thus, they should satisfy certain requirements in order for DYSCs to operate efficiently. In the present research, a photosensitizer, Flavan-3-ol was proposed and graphene quantum dots doped with the nitrogen atom (N-GQDs) were used to modify its attributes. The electronic, optical and geometric attributes of this photosensitizer was probed using DFT as well as time-dependent DFT. In order to validate the basis set and the density functional used in the present study, we used the available data on the parent Flavan-3-ol. There was a substantial narrowing in the energy gap of Flavan-3-ol after hybridization. As a result, there was a shift in the absorption of Flavan-3-ol, i.e., it changed from the UV region to the visible region, thus matching the solar spectrum. Moreover, a light-harvesting efficiency near unity was achieved after an increase in the intensity of absorption intensity, which is capable of increasing the generation of current. We adjusted the newly-designed dye nanocomposites’ energy levels were closely aligned with reduction potential and the conduction band, which indicated the possibility of injecting and regenerating electrons. Based on the attributes of the materials, it can be confirmed that they meet the requirements and can be used in DYSCs.