Lock-in and pulsed thermography for solar cell testing

Inspection of solar cells is an important part of their production process because even small defects can cause a significant drop of a whole photovoltaic module performance. LED illuminated lock-in (LEDILIT) and flash-pulse thermographic techniques (FPT) were compared in this study. Lock-in methods are more commonly used for solar cell inspection. The aim of the study was to discover if the FPT is the appropriate method for inspection of defects of multicrystalline solar cells. Experimental setup, inspection results, and advantages/disadvantages of both methods are presented. It is demonstrated that the LEDILIT is the suitable technique for inspection of defects connected with a photovoltaic effect. Local shunts, cracks, and artificial laser-made defects were detected. Only some of the most significant shunts and laser-made defects were identified by the FPT. However, the FPT inspection is much faster than the LEDILIT. The FPT was also able to indicate an inhomogeneity at a bottom layer of a cell, which was not connected with a photovoltaic effect and not revealed by the LEDILIT.