|Thermal And Electrical Characterization Of Catastrophic Degradation Of Silicon Solar Cells Submitted To Reverse Current Stress|
|Alessandro Compagnin1, Matteo Meneghini1, Valentina Giliberto1, Marco Barbato1, Margherita Marsili2, Enrico Zanoni1, Gaudenzio Meneghesso1,3
1Department of Information Engineering, University of Padua, Via Gradenigo, 6/B 35131, Padova, Italy
/2Department of Physics and Astronomy, University of Padua, Via Marzolo, 8 35131, Padova, Italy
/3Polo Fotovoltaico Veneto, University of Padua, Via Trasea, 7 35125, Padova, Italy
The aim of this work is the reliability evaluation of silicon solar cells submitted to reverse operation. The reverse operation can give origin to very localized spots that (i) limit the lifetime and efficiency of the cell, and (ii) ruin and damage the panel encapsulant, potentially reducing the lifetime of the whole solar panel. The study was carried out by combined electrical, electro-optical and thermal measurements, executed at the different stages of the stress tests. Results indicate that exposure to reverse bias may induce severe modifications of the shunt resistance, due to modifications in the parasitic leakage paths (which can be revealed as hot spots by infrared thermal imaging). The failure of the cell has demonstrated to appear at a critical reverse current level, and is induced both by the high current flow and by the high and very localized temperature reached in correspondence of the shunt path. I-V measurements carried out at different illumination levels provide information on the efficiency and fill factor modifications induced by the decrease in shunt resistance, as well as the kinetics involved in the ageing. Finally the modifications in the electrical characteristics of the cells are simulated by a two-diode model data fitting, which validate the lowering of the shunt resistance and also evaluate the changing in the behavior of the two diodes and the series resistance.