Thin film chalcopyrite solar cells grown on light-weight, flexible substrates are an appealing product. An insulating barrier layer is a requisite for flexible steel substrates to protect the chalcopyrite absorber layer from in-diffusion of iron and also to isolate the solar module, electrically, from the metal substrate. Spray pyrolysis is presented here as a means to deposit an aluminium oxide barrier layer. Optimised spray deposition conditions are investigated and subsequent solar cell results are presented. Resistivity measurements in conjunction with thermography allow assessment of the barrier layer's insulating properties and occurrence of pin-holes in the layer. Resulting Cu(In,Ga)Se(2) cells, with a barrier layer, reach an efficiency of 14.4%. (C) 2010 Elsevier B.V. All rights reserved.