Influence of incorporation of Na on CuInSe2 thin films

We have prepared thin films by rf sputtering from CuInSe₂ and Na₂Se mixture target under the various ratios of [Na]/[CuInSe₂] in the target. The composition of the thin films moved gradually from CuInSe₂ to CuIn₂Se_3.5 as the Na content was increased. X-ray diffraction studies show that the crystal structure of these thin films changed from chalcopyrite to defect chalcopyrite structure. The optical absorption edge of the films is shifted to higher energy with increasing Na content, dependent on the compositional and structural changes of the thin films.