Deterioration of silver alloy electrode caused by photocatalytic reaction for crystalline silicon solar cells

Abstract

In recent years, some minor elements are added into silver paste in order to improve the Ag/Si contact properties for crystalline silicon solar cells. Nevertheless, along with the addition of minor elements, the early discoloration of silver electrode appears on solar cells. In this work, the deteriorated silver alloy electrode on crystalline silicon solar cells was analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The results prove that there exists a small amount of bismuth sulfide on the surface of the deteriorated electrode compared with normal electrode. An important finding is that the photocatalytic reaction of bismuth sulfide can accelerate the early discoloration of the silver alloy electrode. Then, the effect of silver alloy electrode deterioration on the peel force of ribbon for solar cells was investigated. The results indicate that the peel strength between ribbons and solar cells is decreased sharply due to the poor solderability of the deteriorated electrode. Additionally, it is found that the deteriorated silver alloy electrode can be recovered at 450 °C annealing for 60 s in a sintering furnace. After recovery experiments, the average peel force of ribbons attached to recovered busbars is up to 85% of normal busbars. The peel force of ribbon is significantly improved. The results obtained in this paper indicate that more attention should be given to the negative effect of minor elements on the electrode, when minor elements are added into silver paste to improve its performance.