关键词: 密度泛函理论, 染料敏化太阳能电池, 染料D5, 分子设计

Abstract:

Using density functional theory, time-dependent density functional theory and natural bond orbital analysis, we designed D5 analogue molecules, which are superior to the organic dye D5 for use in dye-sensitized solar cells. The symmetric introduction of the electron donating substituents (—OH,—NH2,—OCH3) to the electron donating groups of the D5 skeleton raises the energy level of the lowest unoccupied molecular orbital (LUMO) and causes a red-shift in the absorption spectra. These changes enhance the ability of the dye molecules to capture photons from solar radiation as well improving the driving force for electron injection from the dye molecule's excited state to the TiO2 electrode. The symmetric introduction of electron-acceptors (—CF3,—F,—CN) to the skeleton of D5molecules red-shifts the absorption spectra of the dye molecules greatly, allowing for more efficient use of solar energy. Considering the increase in the LUMO energy level and the red-shift in the absorption spectra, the designed molecules D516, D536 and D537 are superior analogue molecules of D5, of which D516 is the best. By only considering the absorption spectra red-shift, the designed molecules D565, D567 and D568 are superior analogue molecules of D5. Among these, the absorption spectrum of D565 is expected to better match the solar radiation spectrum. The six selected D5 analogues all have D-π-A (donor-conjugate π bridge-acceptor) structures. For these molecules, the transitions from the highest occupied molecular orbital to the LUMO arising from optical excitation are all π-π* intramolecular charge transfer transitions. Their electronic absorption spectra lie in the near-ultraviolet-visible light zone. Compared with D5, D516 and D565 are more applicable for use in DSSC as metal-free organic dye molecules.

Key words: Density functional theory, Dye-sensitized solar cell, Dye D5, Molecular design