Investigation of Accelerated Stress Factors and Failure/Degradation Mechanisms in Terrestrial Solar Cells. Fourth Annual Report

摘要

This annual report presents results of an ongoing research program into the reliability of terrestrial solar cells. Laboratory accelerated testing procedures are used to identify failure/degradation modes which are then related to basic physical, chemical, and metallurgical phenomena. In the most recent tests, ten different types of production cells, both with and without encapsulation, from eight different manufacturers were subjected to a variety of accelerated tests. Results indicated the presence of a number of hitherto undetected failure mechanisms, including Schottky-barrier formation at back contacts and loss of adhesion of grid metallization. The mechanism of Schottky-barrier formation can be explained by hydrogen, formed by the dissociation of water molecules at the contact surface, diffusing to the metal/semiconductor interface. This same mechanism can account for the surprising increase in sensitivity to accelerated stress conditions that was observed in some cells when encapsulated. (ERA citation 08:053775)