A Zn compound buffer layer for Cu(In,Ga)Se-2 (CIGS) solar cells was grown from an alkaline aqueous solution using chemical bath deposition (CBD). To improve the film quality and exclude the cracks in the film, processing parameters such as reagent concentration, deposition time, and temperature profile were varied. Under the optimized CBD process, a uniform and crack-free film was grown on a CIGS substrate with thicknesses ranging from 10 to 60 nm. The controllable thickness of the film was as low as 10 nm. X-ray diffraction and Auger analysis showed that the Zn compound film was in an amorphous state with the ZnSx(OH)(y)O-z composition. A 26% increase in the optical transmittance in the spectral range of 380-600 nm, as compared to a standard CdS buffer layer, was achieved. Finally, by optimization of the CBD process, we formed buffer layers, which enabled the transmission of the short wavelength of the solar spectrum for CIGS absorption. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3212838] All rights reserved.