An In-based buffer layer was deposited by using the chemical bath deposition (CBD) technique from the acetic aqueous solution containing InCl3 and CH3CSNH2 and its structure and optical properties have been characterized. In2S3 and InOOH phases were found in the buffer layer from the combined results of X-ray photoelectron spectra and X-ray diffraction patterns. The growth of InOOH through the chemical bath deposition has not been previously reported. The compositional ratio of In2S3 and InOOH in the film was similar to3. The Auger In MNN peak and the direct band gap of the InOOH phase are 407.1 and 3.5 eV, respectively. A uniform 30 nm thick In-x(OOH, S)(y) film with a tightly connected grain structure was grown by the chemical bath deposition process. The optical transmittance of the In-x(OOH, S)(y) buffer layer was higher than that of CdS buffer layer, due to an indirect band gap of In2S3, suggesting that this new film is a good candidate for the buffer layer of Cu(In, Ga)Se-2 solar cells. (C) 2004 The Electrochemical Society.