Photo-induced charge transfer in defect-free (TiO2)15 nanoparticles and charge transfer from carotenoid to (TiO2)15b nanoparticle in carotenoid-(TiO2)15b complex used for solar cell

(a) The orbital energies and electron densities of HOMO and LUMO of the semiconductor (TiO2)15 (15a and 15b); (b) the efficient charge transfer occurring in carotenoids-(TiO2)15b complex used for solar cell.