Differences in Printed Contacts Lead to Susceptibility of Silicon Cells to Series Resistance Degradation

In this case study, we investigate a degradation mode occurring at the cell level in fielded multi-Si modules. The modules exhibit a mix of affected and unaffected cells. Affected cells show a progressive, series-resistance-related power degradation as shown via module- and cell-level IV curves, along with electroluminescence (EL) and PL imaging at the module, cell, and cell core sample scales. Scanning electron microscopy and energy-dispersive X-ray spectroscopy reveal a difference in the oxides in the silver paste used in screen printing of the gridline contacts. The paste in the affected cells is lead rich, whereas the paste in the unaffected cells is zinc rich. This suggests that the cells were screen printed with different silver paste compositions and possibly firing conditions, and that the different composition correlates with the susceptibility to degradation. Our results indicate degradation of the contact at the oxide-silver interface, causing a severe increase in series resistance across the cell that continues to progress over time.

Automated summary

This case study investigates a degradation mode occurring at the cell level in fielded multi-Si modules. The affected cells show a progressive power degradation due to an increase in series resistance, while the unaffected cells do not exhibit this degradation mode. Analysis of the different silver paste composition and firing conditions suggests that it may be the cause of this degradation.