CuInSe2 thin films were prepared by a three-stage sequential co-evaporation of In-Se, Cu-Se, and In-Se elements for photovoltaic application. After growing CuInSe2 films, the film surface was converted to an ordered vacancy compound (CuIn3Se5). The presence of a CuIn3Se5 layer on the CuInSe2 surface was confirmed by XRD and AES. By the formation of the CuIn3Se5 phase on the CuInSe2 surface, the absorption edge was shifted from 1200 Angstrom to a shorter wavelength. On the CIS films, an In2Se3 buffer layer instead of the commonly known CdS layer was employed and deposited in the same evaporator without breaking the vacuum system. The ITO/ZnO/In2Se3/CuInSe2 cells with a thin CuIn3Se5 layer at the In2Se3/CuInSe2 interface yielded a solar efficiency of 8.46% with an active area of 0.2 cm(2) which is considered high efficiency regarding no Ga in the CIS absorber layer.