Development of the basis for in process metrology for roll to roll production of flexible photo voltaics

This paper reports on the recent work carried out as part of the EU funded NanoMend project. The project seeks to develop integrated process inspection, cleaning, repair and control systems for thin films on flexible PV film based on CIGS (Copper Indium Gallium Selenide CuIn_xGa_(1-x)Se ₂). These films are fabricated on polymer film by the repeated deposition, and patterning, of thin layer materials using roll-to-roll processes, where the whole film is approximately 3um thick prior to final encapsulation. Current wide scale implementation however is hampered by long-term degradation of efficiency due to water ingress through the barrier layer defects to the CIGS modules causing electrical shorts and efficiency drops. A thin (∼40nm) barrier coating of Al₂O₃ usually provides the environmental protection for the PV cells. The highly conformal aluminium oxide barrier layer is produced by atomic layer deposition (ALD). The paper reports initial measurement taken on prototype films and reports on the correlation of water vapour transmission with defect density, it also reports on a new in process, high speed, environmentally robust optical interferometer instrument developed to detect defects on the polymer film during manufacture. These results provide the basis for the development of R2R in process metrology devices.