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.

► A rational design strategy is developed to improve dye sensitizers for solar cells.
► A reference dye is modified using electron-donating (ED) and withdrawing (EW) units.
► Modifications are based on Dewar's rule.
► Both ED and EW substitutes could reduce the HOMO-LUMO gap with different mechanisms.
► Substitutions close to the donor-part of the reference dye are suggested.