Molecular Design of Porphyrins for Dye-Sensitized Solar Cells: A DFT/TDDFT Study

To design efficient sensitizers for dye-sensitized solar cells (DSSCs), a series of porphyrin sensitizers with different electron-donating and withdrawing substituents are investigated using the density functional theory (DFT) and time-dependent DFT approach. We found that the designed dyes have smaller highest occupied molecular orbital to lowest unoccupied molecular orbital (HOMO-LUMO) energy gap values, and the absorption bands are broadened and shifted to longer wavelengths compared to the so far best sensitizer (YD2-o-C8). Importantly, our designed dyes have larger contributions of the anchoring group to the LUMOs, which enhance the electron injection process. Our calculation results indicated that the new systems should have better performance than the existing efficient dyes due to their improved optical properties.