Theoretical design of highly efficient porphyrazine solar cells

Density functional theory and time-dependent density functional theory methodologies have been applied to design porphyrazine (tetraazaporphyrin) sensitizers. This was done by replacing the porphyrin macrocycle cavity with a porphyrazine macrocycle cavity and increasing the number of p-carboxyphenyl moieties at the macrocycle periphery so that the performances of the suggested cells could be expected to exceed the efficiency of the reference YD2-o-C8 porphyrin sensitizer with Ti38O76, (TiO2)(60), SiC, ZrO2, and GaP semiconductor electrodes. Macrocycle replacement assists in promoting the efficiency in the red shoulder of the spectrum more effectively than increasing the number of anchoring groups. The expected effects of the former structural modifications on cell performances are confirmed in terms of natural transition orbitals, energy gaps, semiconductor valence bands and conduction band edges, density of states, UV-visible absorption, and lifetimes of the excited states Phi(LHE), Phi(inject.), and Delta G(regen). The structural modifications resulted in charge-separated states, unidirectional charge transfer, narrower band gaps, increase of density of states nearby Fermi levels, delocalization of the negative charges near the anchoring groups, efficient light harvesting and electron injection, suppressing macrocycle aggregation, active dye regeneration, and inhibited dye recombination. Co-sensitizers are suggested for near-infrared sensitization.