Oxides related to cadmium telluride solar cells*

Polycrystalline cadmium telluride (CdTe) is a leading material in photovoltaic technology due to its high absorption coefficient and near-optimum bandgap of 1.44 eV. It is known that CdTe film processing can promote surface oxidation depending on the growth environment and upon exposure to different oxidation conditions. For example, CdTeO₃ forms when the CdTe film is treated in heated dry air, while in humid air, CdTe₂O₅ is detected. These oxides feature tellurium in the oxidation state +4 compared to the +2 state in CdTe. Other possible relevant oxides are CdO, TeO₂, and TeO₃. Using hybrid density functional calculations, we studied the electronic structure of these oxide materials and their band alignment to CdTe, which are essential parameters in the characterization of the interfaces at grain boundaries. The goal is to understand their stability and possible effects on passivating grain boundaries. The results are compared to the available experimental data.