Interface properties and band alignment of Cu_2S/CdS thin film solar cells

摘要

The stoichiometry and electronic properties of bulk Cu_2S thin films obtained by vacuum evaporation were investigated by optical spectroscopy, X-ray diffraction and photoemission spectroscopy. The Cu_2S/CdS heterojunction interface has been prepared in situ and characterized by photoelectron spectroscopy (X-ray photoemission spectroscopy and ultraviolet photoelectron spectroscopy) after each growth step under ultra high vacuum conditions. The XPS core level spectra as well as valence band spectra of the substrate Cu_2S and overlayer CdS were acquired after each step. From these measurements, a large overall band bending of 0.9 eV is observed. The valence band offset is determined to be ΔE_(VB) = 1.2 eV and the conduction band offset is ΔE_(CB) = 0 +- 0.1 eV.