Ab initio molecular electronic structure computations have been performed employing DFT and TD-DFT methodologies
to optimize the performance of two types of DSSCs. This was done by tuning the frontier orbital energy
gaps, adding low cost transition metal atoms (Zn, Ni, Fe, Ti) to the porphyrin donor, and strongly activating
electron donating groups (NMe2) to the fullerene acceptor. The results reveal that cell efficiency has been significantly
enhanced by metal functionalization of the donor, and the electron donating capabilitiy of the acceptor.
While Ti-porphyrin was found to be the most efficient dye sensitizer for DSSCs based on porphyrin donors and
substituted fullerene acceptors, Fe-porphyrin was found to be the most efficient sensitizer for DSSCs based on
porphyrin donors and a series of oxide semiconductor acceptors. Fe dye can sensitize several oxide semiconductor
acceptors in [Co(dmb)3]n+ redox electrolyte, and cell efficiencies of Ti dyads can exceed (4.8%). The
metal atoms and the electron donating groups facilitate rapid electron injection from the donor moiety to the
acceptor moiety and narrow the band gaps of both of the donors and acceptors so that the density of states
near the Fermi levels scales linearly with the photovoltaic conversion efficiency. The introduction of low cost Fe
and Ti to the free base porphyrin leads to more active non linear optical performance, stronger response to
the external electric field, and induces higher photo-to-current conversion efficiency. Fe and Ti also red shift the
electronic absorption bands of the free base porphyrin, and make it a potential candidate for harvesting light in
the entire region of solar spectrum. |
