A new method is proposed for the fitting of laser reflectance monitoring of a roughening film surface. This has been applied to the metal organic chemical vapour deposition (MOCVD) of the CdS/CdTe photovoltaic structure, grown onto ITO-coated glass substrates. It was found that the fitted roughening parameter, F-rs. correlates with the organometallic VI:II ratio in the CdTe layer growth. In particular, the slope of this parameter, giving the rate of roughening, has been quantified and relates to the series resistance of the solar cell. For the first time we now have an in situ measurement for this photovoltaic structure which provides an indication of one important factor in the device performance and could eventually be used as a process monitor.