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Understanding the Role of Impurity Level in the Screen-Printed Front Silver Paste for High Sheet Resistance Emitter Silicon Solar Cells
Keywords: Ag paste, high sheet emitter, Si solar cell
The front silver screen-printed paste plays a major role in forming a high quality contact to high sheet resistance emitters. The glass frit is important for adhesion and etching of antireflection coating to allow the silver and silicon to interact and forms silver crystallites. The silver crystallites are essential for carrier transfer into front metal grid. In this mixture of silver powder, organics and glass frit, the purity of the front silver paste is critical, especially for emitters with <0.3 m junction depth. In this paper we report on use of three front silver pastes with varying impurity levels (low (paste A), medium (paste B) and high (paste C)) to form high quality contacts to high sheet resistance emitters. We used the float zone to remove any variable other than the impurities in the front silver pastes. We achieved 17.6%, 17.5% and 17.3% efficiencies, respectively, for cells using the front silver paste A, B and C. Cells made with paste A showed excellent ideality factor of 1.03 and the dark saturation current density (Jo2) of 7.3 nA/cm2. However, high ideality factor of 1.24 and Jo2 of 41.8 nA/cm2 were shown for cells using paste C. This study shows the impurity level in the front silver paste is important in fabricating solar cells with low junction leakage.
Abasifreke Ebong,
Georgia Institute of Technology
Atlanta, GA
USA


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