Comparison of Outdoor and Indoor PL and EL Images in Si Solar Cells and Panels for Defect Detection and Classification

Nowadays, silicon solar plants consist of hundreds of thousands of panels. The detection and characterization of solar cell defects, particularly on-site, is crucial to maintaining high productivity at the solar plant. Among the different techniques for the inspection of the solar cell defects, luminescence techniques provide very useful information about the spatial distribution of defects. Electroluminescence performed in dark conditions (nEL) is the most commonly used technique. However, daylight EL (dEL) and daylight photoluminescence (dPL) have recently attracted interest, because they present noteworthy advantages for on-site inspections. In this paper, we present a detailed characterization of both damaged mono- and multi-crystalline silicon solar cells using dEL and dPL, comparing the results provided by these techniques with those obtained with high-resolution nEL and indoor PL (performed under excitation with a laser diode). Among these techniques, dEL provides reliable and reproducible results, while dPL shows more dependence on the experimental conditions, demanding additional efforts for analysis. The limited resolution obtained with the actual IR camera technologies is a limiting factor of the dEL and dPL techniques. On the other hand, they can be performed on-site, testing a very large number of panels. Therefore, we can assert that on-site dEL is well suited for massive inspection of solar plants, while more research is necessary for dPL.