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Comprehensive analysis of advanced solar cell contacts consisting of printed fine‐line seed layers thickened by silver plating
Author(s) -
Pysch D.,
Mette A.,
Filipovic A.,
Glunz S. W.
Publication year - 2009
Publication title -
progress in photovoltaics: research and applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.286
H-Index - 131
eISSN - 1099-159X
pISSN - 1062-7995
DOI - 10.1002/pip.855
Subject(s) - crystallite , contact resistance , materials science , layer (electronics) , plating (geology) , electrical contacts , composite material , electrical resistivity and conductivity , metallurgy , electrical engineering , engineering , geophysics , geology
This work presents a detailed analysis of a new two‐layer process to contact industrial solar cells. However, most of the results seem to be transferable to standard screen print paste contacts. The seed layer was created by a pad or screen printer and thickened by light‐induced plating (LIP) of silver. These contact structures were investigated microscopically to gain a better understanding of the observed electrical parameters. A review of the present microscopic contact formation model for flat surfaces is presented. This model was extended and applied to surfaces textured with random pyramids. This analysis has revealed two new types of silver crystallites which can be described by a crystallographic model. The dependence of the silver crystallite density on the surface doping concentration was investigated. Next, the dependence of the contact resistance on the width of the seed layer was measured showing that the contact resistivity increases with a reduction of the seed layer width. These results have been further approved by an analysis of SEM images of wet‐chemically etched contacts examining the density of crystallites and the fraction of removed SiN x layer. Contact resistance R C measurements before and after LIP of silver showed surprisingly a positive influence of the plating process on R C . A detailed microscopical analysis revealed four new possible current flow paths due to the LIP of a conventional contact or a seed layer. The results led to an extension of the existing model for a screen‐printed contact. Copyright © 2008 John Wiley & Sons, Ltd.