In-line metrology of functional surfaces with a focus on defect assessment on large area Roll to Roll substrates

This paper reports on the recent work carried out as part of the initial stages of the EU funded NanoMend project. The project seeks to develop integrated process inspection, cleaning, repair for nano-scale thin films on large area substrates. Flexible photovoltaic (PV) films based on CIGS (Copper Indium Gallium Selenide CuInxGa(1-x)Se2) have been reported to have light energy conversion efficiencies as high as 19%. CIGS based multi-layer flexible devices are fabricated on polymer film by the repeated deposition, and patterning, of thin layer materials using roll-to-roll processes (R2R), where the whole film is approximately 3μm thick prior to final encapsulation. The resultant films are lightweight and easily adaptable to building integration. Current wide scale implementation however is hampered by long term degradation of efficiency due to water ingress to the CIGS modules causing electrical shorts and efficiency drops. The present work reports on the use of areal surface metrology to correlate defect morphology with water vapour transmission rate (WVTR) through the protective barrier coatings.