Laser Induced Luminescence Characterization of Mechanically Stressed PV Cells

Electroluminescence (EL) and photoluminescence (PL) imaging are powerful solar cell and panel characterization techniques that are capable of detecting early stage solar cell failures and degradation with high sensitivity and level of detail required for proper preventive maintenance. The electrical contacts needed during measurement pose a challenge for many inspection scenarios, both for EL and PL. Light or Laser induced luminescence (LIL) is a contactless way to generate spatially resolved images of PV panels that highlight poorly connected cell areas, such as finger failures, areas with high series resistance or disconnected cell cracks. In this study, we analyze the characteristics of the LIL scan imaging method in detecting cracks in mono-Si cells, comparing single frames with reconstructed contactless EL images built with a full LIL scan image stack. A comparison between contactless EL generated by LIL and conventional contact EL is made, and finally an estimation of the required laser intensity for outdoor LIL is provided, in correlation to known contact EL performance during nighttime and daylight conditions.