Molecular design and theoretical investigation on novel porphyrin derivatives for dye-sensitized solar cells

We report on a quantum-chemical study of the electronic and optical properties of a series of beta, beta'-edge-fused zinc porphyrin with different aromatic rings, in order to design efficient sensitizers for dye-sensitized solar cells (DSSCs). Our calculations found that the replacement of quinoxaline moiety in ZnQMA (having high power conversion efficiency g of 6.3%) with other aromatic rings decreases the HOMO-LUMO energy gap mainly due to destabilization of the HOMO level. For all of the investigated compounds, the reorganization energies of electron and hole are in the same order of magnitude as and similar to those of ZnQMA. The absorption spectra in both Soret and Q bands for most of the considered molecules exhibit red shifts to some extent with respect to that of ZnQMA. In the simulated dye-sensitized TiO2 systems, the bidentate adsorption mode of porphyrin derivatives is computed to be energetically favored compared to the monodentate one, which well confirms the experimental results observed by X-ray photoelectron spectroscopy. The slightly shorter Ti-O bond lengths calculated for D-TiO2 systems point toward a stronger interaction of the dye with the titania surface compared to ZnQMA-TiO2 systems. Our calculation indicates that the designed molecule D is promising to challenge the current photoelectric conversion efficiency record 6.3% of ZnQMA