A major challenge in the fabrication of high band gap II-VI polycrystalline solar cells is to preserve the original composition of the absorber after the CdCl2 activation treatment. In this study, a method is demonstrated to maintain the Cd-Zn-Te alloy absorber composition during its exposure to the CdCl2 treatment. A thin film of CdS was applied as a barrier on the back surface of the high band gap polycrystalline Cd(1-x)ZnxTe (x = 20% by atomic ratio, corresponding band gap 1.72 eV) before the CdCl2 treatment. Using transmission electron microscopy and energy dispersive spectroscopy, it was observed that the composition of Cd-Zn-Te was maintained after the CdCl2 treatment. The devices fabricated after removing the thin film of CdS, exhibited diode-like behavior. A significant increase in the quantum efficiency near the short wavelength region was observed, and the band gap of Cd(1-x)ZnxTe was maintained.