A study of junction position and uniformity in CdTe/CdS solar cells is reported in which the influence of excluding oxygen from the CdS layers was investigated. The samples were characterised with an optical beam induced current instrument capable of mapping the cell response in the range 400-900 mu m at a resolution of 12.5 mu m - either as a map or a quantum efficiency spectrum. For oxygen-free CdS, the junctions were always buried in the CdTe - at a depth presumed to be controlled by the chloride treatment. If CdS:O is used then shallow junctions result, indicating that such layers have a role in doping the devices. The wavelength dependence of the spatial uniformity of the cell's responses is also discussed. (C) 2008 Elsevier B.V. All rights reserved.