Silicon Solar Cells with Nickel/Solder Metallization

Summary

Nickel/solder metallization of silicon solar cells offers a relatively inexpensive method of making electrical contact with the surface of the cell. More expensive methods, using precious metals and costly processes, are extensively used, having been developed for space applications. More recent interest in terrestrial applications of solar cells has led to an increased concern over cost, and nickel has assumed a position as a major candidate for solar cell metallization. Nickel can be plated on silicon solar cells using an electroless chemical deposition method to give contacts with good adhesion. In some cases where adhesion is poor initially, possibly as a result of surface contamination on the silicon, sintering under relatively mild conditions will dramatically improve the quality of the bond without harming the p-n junction of the cell. Silicon dioxide films of uncontrolled thicknesses have been considered to be a major cause of poor adhesion, but we have demonstrated that the electroless nickel plating solution dissolves silicon dioxide before depositing nickel. Silicon solar cells with nickel/solder metallization can survive terrestrial environmental stresses, as demonstrated by a 1,000 hour test at 85°C and 85% relative humidity under constant forward bias of 0.45 volt.