Carrier lifetime improvement in D-π-A systems; Molecular engineering of the dye-sensitized solar cell

This work is a computational study on the molecular engineering of the dyesensitized solar cells (DSSCs). The studied dyes have been designed in the donor-π spacer-acceptor (D-π-A) forms marked as 5 -(9-(4-Fluorophenyl)-9H-carbazol-3-yl)- [2,2 -bithiophene]-5-carbaldehyde (3p), (E)-5 -(4-(Pyrrolidin-1-yldiazenyl)phenyl)-[2,2 - bithiophene]-5-carbaldehyde (3v) (Fig. 1).The study of the ground state and molecular orbitals of the dyes have been done via density functional theory (DFT)and natural bond orbital (NBO) analysis [1]. Since excited state lifetime of the dyes is one of the most important challenges related to the performance of the dyes, it has been investigated through the time-dependence DFT (TD-DFT) method [2]. According to the energy alignment of the molecular orbitals, the selected molecules can be applied as the dyes in the DSSCs. Here, the effects of different donors on the performance of the DSSCs have been considered, specially. Results show a stronger D part can facilitate electron injection from the dye to the TiO2, due to a greater intramolecular electron transfer. Moreover, a more efficient D-π-A model of the dye leads to an improved life time of the excited states. The calculated Gibbs energies of the electron injection from the dyes to the semiconductor in the DSSCs are enough low to transfer electrons in an efficient path.

Keywords:

Lifetime , Dye , Gibbs energy , Molecular engineering , Electron donor , DSSC