Simplified detection method of the rear-side weak soldering for monofacial solar cell using electroluminescence quantitative technology

Abstract

In the series soldering step of photovoltaic module manufacturing process, soldering could be occasionally found weak or missing between busbar and interconnection ribbon. The affected modules have local heating phenomenon in application, which aggravates modules efficiency degradation. Electroluminescence (EL) technology can detect many module defect types including weak soldering. But the grayscale change of EL image is not obvious enough caused by rear-side weak soldering (RWS) compared with front-side weak soldering, especially for monofacial solar cell. RWS is difficult for manual qualitative identification. In this paper, we use EL quantitative technology and simply define deviation percentage (Si) to distinguish types of weak soldering. RWS can be effectively detected through grayscale analysis of EL images under two different bias current conditions, which is verified by experiments and simulation. Further simulation results suggest that higher rear-side lateral resistance leads to lower Si of RWS. This method is instructive for the automatic EL detection in module production line.