Electronic structure at the interfaces of vertically aligned zinc oxide nanowires and sensitizing layers in photochemical solar cells

Abstract

Vertically aligned zinc oxide (ZnO) nanowires (NWs) coated with cadmium telluride (CdTe) shell layers via simple evaporation have been used to fabricate photochemical solar cells. The narrow bandgap of CdTe (∼1.45 eV) enhances the optical absorption in the range of visible light. The detailed electronic structures of ZnO/CdTe and ZnO/Dye were investigated and compared with the aid of ultraviolet photoemission spectroscopy. The analysis shows electric dipole at the ZnO/dye interface due to Zn 2+ /carboxy bonding while no significant bonding existed at the ZnO/CdTe interface. The ZnO/CdTe interface is a characteristic of a small heterojunction barrier where the excited electrons can be transferred to the conduction band of ZnO NWs through defect levels. The average stable short circuit current density taken at the fifth minute of light illumination for the photochemical solar cell reaches 4.69 mA cm −2 , while it is only 3.90 mA cm −2 for in situ dye sensitized solar cells.