The chemical changes between transparent conducting oxide (TCO) and cadmium sulphide (CdS) layers were analyzed using X-ray photoelectron spectroscopy (XPS). Commercially available indium tin oxide (ITO) and ITO/SnO2 were used as substrates. The CdS layers were deposited in vacuum (similar to 10(-2) Pa) at two different (low and high) substrate temperatures by close spaced sublimation technique. During the growth of CdS layer, the substrate temperature was increased from 25 to 25 degrees C for low temperature layer and from 490 to 550 degrees C for high temperature CdS layer due to the high crucible temperature. Similar to CdTe solar cell device process steps, the samples (TCO/CdS) were annealed in vacuum (10(-2) Pa) at 520 degrees C and in air at 375 degrees C with and without CdCl2. The XPS depth profile analysis shows that annealing ITO/CdS sample in vacuum induces diffusion of indium into the CdS layer from ITO. The most of the diffused indium atoms are found on top of the CdS layer. No indium diffusion into the CdS layer was observed for the TCO with SnO2 buffer layer between ITO and CdS. However, at SnO2/CdS interface Cd atoms diffuse into the SnO2 buffer layer after CdCl2 activation. The change in chemical and electronic properties of the ITO/CdS and ITO/SnO2/CdS interfaces is discussed in detail. (C) 2013 Elsevier B.V. All rights reserved.