First-principles investigation on electronic properties of quantum dot-sensitized solar cells based on anatase TiO₂ nanotubes

The first-principles quantum mechanical investigation on CdS quantum dots (QDs) adsorbed on anatase TiO₂ nanotubes (TiO₂NTs) in quantum dot-sensitized solar cells (QDSSCs) was performed using the density functional theory (DFT) approach. The geometry and electronic coupling between a CdS QD and the TiO₂NT have been examined for the first time, together with a detailed discussion of interfacial electron transfer and electron transport models along the TiO₂NT. It has been found that adsorbate states are introduced in the band gap of the TiO₂NT upon the adsorption of a CdS QD on the TiO₂NT surface, and an electron transfers from the sulfur atoms of a CdS QD to the conduction band of the TiO₂NT upon adsorption of visible light. The unique TiO₂NT structure offers a one-dimensional directional pathway for electron transport across the semiconductor substrate through titanium d_x2-y2 and d _z2 orbitals. Our work is of great benefit for understanding the charge separation process at the heterogeneous interface and the key factors to govern the electron transport efficiency in TiO₂NTs.