Ultrahigh vacuum preparation and characterization of TiO2/CdTe interfaces: Electrical properties and implications for solar cells

The semiconductor cadmium telluride (CdTe) has been grown in ultrahigh vacuum by standard molecular beam epitaxy on thin films of anatase titanium dioxide (TiO2) to investigate the interface properties of solid state injection type solar cells. These interfaces were studied by photoelectron spectroscopy and the band alignment was determined. The interface is characterized by a valence band offset ΔEV of 2.6 eV, a conduction band offset ΔEC of 0.7 eV, and a strong dipole δ of about 0.9 eV in contradiction to the electron affinity rule (Anderson model). Therefore this system is not very favorable for solar power generation.