The 20.9% conversion efficiency of I-III-VI chalcopyrite-based solar cells, the highest in the world, makes them promising candidates for high-efficiency thin film solar cells. However, Ga is one of the most expensive rare materials with the critical degradation in device efficiency. Cu(ln(1-X)Al(X))Se2 (CIAS) is considered an alternative to Cu(ln(1-X)Ga(X))Se2 because of its good structural suitability and the low cost of Al. CIAS thin films were formed using triple targets of CuSe2/ln/Al in a co-sputtering system to control the composition ratio, x = [Al]/([ln]+[Al), by varying each RF power for In/Al with rapid thermal annealing. The chalcopyrite peaks shifted toward higher 2theta as x increased. The CIAS thin films had 74.24-86.81% absorption with band gap, Eg, of 2.28-2.50 eV in the 400-1600 nm range. A low resistivity of 1.1 x 10(-2) omega(-cm) was obtained in the CIAS thin films with x of 0.74.