Toward rational design of organic dye sensitized solar cells (DSSCs): an application to the TA-St-CA dye.

A computer aided rational design has been performed on TA-St-CA dye sensitizer in order to improve the desirable properties for new organic dye sensitized solar cell (DSSC). A number of electron-donating (ED) and electron-withdrawing (EW) units based on Dewar's rules are substituted into the π-conjugated oligo-phenylenevinylene bridge of the reference TA-St-CA dye. The effects of these alternations on the molecular structures and the electron absorption spectra are calculated using time-dependant density functional theory (TDDFT). It is found that chemical modifications using electron donating (ED) substitutions exhibit advantages over the electron withdrawing (EW) substitutes to reduce the HOMO-LUMO energy gap as well as the electron distribution of the frontier orbitals of the new dyes. Dewar's rule is a useful guideline for rational design of new dye sensitizers with desired HOMO-LUMO gap. The impact on the optical spectra of new dyes are, however, less significant.