Optoelectronic properties of Portulacaxanthin III (PXIII), GQD/Os-GQD-PXIII nanocomposites, and their coupling with photoanode in dye-sensitized solar cells: Molecular and periodic DFT calculations

In this work, the optoelectronic properties of a naturally occurring dye, Portulacaxanthin III (PXIII), were investigated. To improve the performance of PXIII dye, it was hybridized with graphene quantum dot (GQD) undoped and doped with Os at the central position to form two nanocomposites (PXIII-GQD and Os-GQD-PXIII), and their optoelectronic properties were also investigated. Parameters such as frontier molecular orbital energies and distributions, absorption and emission properties, excited-state lifetimes, and hole and electron reorganization energies were calculated at two molecular (HCTH and CAM-B3LYP) DFT functionals and their counterparts TDDFT functionals in the gas phase and with the PCM model to mimic the effect of the solvent in three solvents: chloroform, acetonitrile, and water. The variation of the abovementioned molecular parameters as a function of media polarities (dielectric constants) was investigated. In addition, the coupling with the photoanode TiO2 anatase (101) with a periodic DFT functional was also investigated. The output from this work demonstrated the better overall performance of the nanocomposites (doped and undoped). Since they have better energy level alignments, red-shifted and broader absorption in the Vis and IR regions, better HOMO and LUMO charge separation, and stronger adsorption on the photoanode.