The crystal structure of the ordered defect compound (ODC) CuIn₅S₈ was established and its properties were studied and compared with CuInS₂. Further, ZnSe and CuI were chosen as the buffer layers of CuInSe₂ and CuInS₂ solar cells respectively. The valence band offset （VBO） was calculated based on the first principle calculation. On the ZnSe/CIS interface, the valence band maximum (VBM) of CIS was higher than that of ZnS with a VBO by about 0.52 eV due to a larger p-d repulsion in CIS. On the CuI/CuInS₂ interface, VBM of CuI was lower than that of CuInS₂ with a VBO of about 0.37 eV. The p-d repulsion was much weaker in ODC compared with CuInSe₂ and CuInS₂, resulting in a lower VBM.