LAUSR

Quantum dot-sensitized solar cells (QDSSCs) are becoming a viable alternative in the market of the third-generation solar cells. Replacing conventional TiO2 or ZnO thin films with anatase TiO2 nanotubes (NTs) leads to a faster charge separation of the excited electron from the quantum dot (QD) to the anode and, consequently, to higher efficiencies. In addition, the adsorption mode of the QDs to the nanotube plays a significant role in the quest for more efficient QDSSCs. We investigate these effects by means of density functional theory (DFT) and real-time time-dependent DFT. Differently sized QDs [(CdSe)13 and (CdSe)34, bare clusters and saturated with methylamine and p-toluidine] are added to different anatase TiO2 nanotubes [NT(0,8), NT(0,12), NT(0,16)]. We considered direct adsorption or linkage via mercaptopropionic acid (MPA). First, the nanotube diameter does not affect the electronic absorption spectra. When the QDs are linked with MPA, we find that the absorption spectrum resembles that of the single QD. Also, the size of the QD has a significant impact on the absorption spectrum and it can happen that the conduction band (CB) of an unsaturated QD lies below that of the nanotube. Saturation of the QD’s surface pushes the CB up again. Furthermore, aromatic ligands increase the first absorption peak maximum to higher energies.