The experimental result for(agg) vs. the photon energy, hv, for the RTA-CZTSe film is shown in Fig. 6. For a direct band gap semiconductor, the absorption coefficient can be evaluated by relation a A(hv-Eg) Ihy, where Eg is the optical energy gap.The band gap of the RTA-CZTse film is determined from the x-intercept as shown in Fig. 6.It is apparent that the band gap of the RTA-CzTse film is 0.98 ev, which is than that of CzTs(about 1.5 e) materials. The optical absorption coeffcient is in the order of 104 cm in the visible region.