Detailed analysis of fine line printed and plated solar cell contacts
This work presents a detailed analysis of the new two-layer process to contact industrial solar cells. The seed layer was created by a pad printer and thickened by light-induced plating of silver. These contact structures were investigated microscopically aiming for a better understanding of the observed solar cell results. First we analysed the influence of the geometry of the seed-layer on IV-parameter. Next, the dependence of the contact resistance on the width of the seed-layer was measured and compared with theoretical expectations. This comparison resulted in the conclusion that the contact resistivity decreases with a reduction of the seed layer width. These results have been further approved by an analysis of SEM-pictures of wet chemically etched contacts. Contact resistance (Rc) measurements before and after light-induced plating of silver showed surprisingly a positive influence of the plating process on Rc. A detailed microscopical analysis revealed four new possible current flow paths due to the light-induced plating of a conventional contact or a seed layer. The results led to an extension of the existing model for a screen-printed contact.