Metrology for in process metrology for roll to roll production of flexible photovoltaics

This presentation reports on the latest development taking place within the EU funded NanoMend project. The aim of the project is to develop integrated process inspection, cleaning, repair and control systems for thin films on flexible photo voltaic films based on CIGS (Copper Indium Gallium Selenide CuInxGa(1-x)Se2). Flexible PV 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. Take up of such devices, especially for building integrated applications BIPV, 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. To address this problem 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 presentation reports initial measurement and characterisation of prototype films. Characterisation is based on the application of segmentation analysis and where the film is considered to be a special case structured surface and defects are considered as structural elements. Characterisation then allows the correlation of water vapour transmission with defect density to be addressed. The paper 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