Comparative study between online and offline defect assessment methods for roll to roll flexible PV modules

Flexible PV modules are manufactured using roll to roll (R2R) technology. These modules require a flexible barrier material to prevent water vapor ingress. The basic methodology to produce such barriers is to combine oxide layer (e.g. AlOx) coating with suitable polymer substrates. However, micro and nano scale defects can appear at any stage of the coating process thus affecting the module efficiency and lifespan. To guarantee the barrier properties, surface inspection needs to be carried out during the manufacturing process. In the present study a stabilised in-line detection system based on wavelength scanning interferometry (WSI) has accurately and reliably captured defects down to 3um in lateral dimension. The main aim of this research paper is to compare results of coherence correlation interferometry (CCI) as an offline technique with WSI results for detecting PV barrier film defects. The results show the capability of the WSI to be implemented in the manufacturing environment for defect detection in roll to roll manufacture.