P-type polycrystalline copper-indium diselenide, $CuInSe_2$, thin films as a absorber in CdS/$CuInSe_2$ solar cell have been prepared by depositing In/Cu layer, which was sequentially sputtered varying the In/Cu mole ratios, on alumina or glass substrate and by selenizing at various selenization conditions with selenium metal vapor in a nitrogen atmosphere. Compositional and structural characterization for thin films was carried out by X-ray diffraction (XRD), wavelength-dispersive spectroscopy (WDS), auger electron spectropscopy (AES), and scanning electron microscope (SEM). Electrical characterization was carried out by the measurements of Hall voltage and electrical resistivity. Large indium loss and selenium deposition occur in early stage of the selenization process. The sheet resistance and crystallinity of the films selenized on alumina substrate vary with increasing selenization time, in 1hr of the selenization process, due to the diffusion of selenium element deposited on the surface of the sputtered film. The stable electrical properties of the selenized films can be obtained after the selenization of 1hr. The indium loss in the films selenized for 1hr with the increasing selenization temperature is accomplished with an increase in the amount of $Cu_xSe$ phase at lower temperatures and with a decrease in the crystallinity of $CuInSe_2$ phase at higher temperatures. The minimum of indium loss in the selenized In/Cu films occurs at the selenization temperature of 450℃. The variation of the electrical properties in the selenized films with the selenization temperature is due primarily to that of hole concentration. The variation of the hole concentration with the selenization temperature is attributed to the indium loss away from the sputtered In/Cu layer. As the amount of copper in the sputtered In/Cu layers increases, the electrical resistvities of the films selenized at 450℃ decrease with an increasing amount of $Cu_xSe$ phase. It is because an increase in the amount of the $Cu_xSe$ phase with the high hole concentration enhances the hole concentration of the selenized films. The electrical resistivities of the selenized films also depends on the sputter sequence of metal layer because the copper layer in the sputtered Cu/In/substrate composites prevents the In-Se reaction and the loss of indium element during the selenization. The variation of the electrical resistivity with the sputter sequences of metal layer can be explained by the increase in the hole concentration in terms of amounts of $Cu_xSe$ phase. By optimizing the sputter conditions and removing the $Cu_xSe$ phase, it is possible to fabricate $CuInSe_2$ thin films which have an appropriate hole concentration ($10^15-10^16cm^{-3}$) for solar cell appication regardless of the sputter sequences of metal layer. On the other hand, the films formed by selenizing the sputtered In/Cu layer on glass substrate show about the same properties with that selenized on alumina substrate. Heterojunction solar cell with structure of CdS/$CuInSe_2$/Mo/glass were fabricated by depositing CdS layer, by vacuum evaporation, on $CuInSe_2$/Mo/glass composites.
