Investigation of the effect of forming gas annealing on front silver electrodes of c‐Si solar cells

Forming gas annealing (FGA) is an effective process to repair low efficiency crystalline silicon (c‐Si) solar cells with overfired screen‐printed paste electrodes. An experimental study was performed to investigate the effect and mechanism of FGA treatment on front silver electrodes of c‐Si cells. To facilitate the FGA mechanistic study, special simulation samples were prepared to magnify the FGA effects on glass frit and overfired electrodes. The micro‐morphology (from cross‐sectional X‐SEM) and elemental composition (from energy‐dispersive X‐ray spectroscopy) data revealed few Ag crystallites in the paste/Si interface because of the thick glass layer from the paste overfiring. The FGA treatment induced phase crystallization (from X‐ray diffraction) in the paste and increased the glass wettability on both Si and Ag substrates, thus resulting in a thinner glass layer, which expedited the precipitation of more pyramidal Ag crystallites at the Ag/Si interface. The wetting angle data of glass samples measured before and after FGA confirmed the mechanism of FGA and concluded that the improvement of glass wettability benefited to reduce the glass layer thickness. As a result, more Ag crystallites diffused toward and precipitated at the Si interface contributing to a lower contact resistance between the paste electrode and the Si matrix and thus improved electrical properties for overfired c‐Si cells. Copyright © 2012 John Wiley & Sons, Ltd.