Multi-laser LBIC system for thin film PV module characterisation

Non-destructive spatial characterisation tools are essential for the evaluation of thin film photovoltaic modules; as such distributed variations have a significant effect on the overall device performance. A combination of several techniques (solar simulator, LBIC and thermography) is used in conjunction to identify and investigate performance problems and locate possible defects in thin film silicon photovoltaic modules of different structures. An excellent agreement between the different spatial analysis tools is demonstrated. The LBIC system used here is unusual in that it analyses modules where the cells are interconnected and the signal strength does not give as clear a feedback on the defects as in the case of measuring each cell separately. The choice of lasers used in the system allows the investigation of separate junctions in the most common multi-junction devices. The system characterisation is demonstrated here in order to warranty reliability and repeatability of this tool. A special test module is investigated where all techniques are compared and good agreement is demonstrated. Furthermore, the problem of reducing signal strength with increasing junction number is demonstrated and discussed.