Figure-8: SCC-DFTB calculated excitation spectra for bare dyes and the dyes adsorbed on (TiO₂)₉₆QD in the form of QD-D system whereas D = D1, D1A, D2, D2A, D3 and D3A.

In order to model the mechanism and determine the driving force for photoinjection, the relevant parameters were calculated for the series of dye-(TiO₂)₉₆ complexes. The energy required for photoinjection is ∆G_inj(eV)= E_LUMO-E_CBM whereas the energy of electron recombination is ∆G_rec(eV)= E_CBM-E_HOMO. The findings indicated that D2-(TiO₂) ₉₆ system required minimum energy of -0.11 eV for electron injection with high recombination energy of 1.18 eV which reveals that electron injection is more favorable than electron recombination. The complex D2A-(TiO₂)₉₆ requires -0.17 eV for electron injection as second minimum value which is less than the recently reported carbazole based organic dyes [85]. The values calculated for all dye-(TiO₂) ₉₆complexes are given in table 3.