The growth of CuIn3Se5 layer on bulk CuInSe2 films has been studied for the fabrication of CuInSe2 solar cells, using the three-stage process which involved the sequential evaporation of In-Se, Cu-Se, and In-Se elemental sources. After growing CuInSe2 films, the film surface was converted to a defect chalcopyrite (CuIn3Se5) compound. The X-ray diffraction and AES depth analysis indicated the formation of the CuIn3Se5 phase on the CuInSe2 surface. By the formation of the CuIn3Se5 phase, the absorption edge was shifted from 1200 to 1000 nm wavelength and the binding energies of Cu, In, and Se were shifted to higher energies. The current-voltage curves of In2Se3/CuInSe2 cells fabricated with a thick CuIn3Se5 layer on a CuInSe2 film displayed a kink effect which was possibly caused by the increase of series resistance and light absorption in the CuIn3Se5 layer instead of the junction region. The cells with a thin CuIn3Se5 layer at the In2Se3/CuInSe2 interface yielded solar efficiency of 8.46% with an active area of 0.2 cm(2).