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

摘要

This is the final report of a reliability research program to study the response of amorphous silicon colar cells to accelerated temperature testing. The goal of the research was to utilize accelerated testing to identify failure/degradation modes and to relate them to basic physical, chemical, and metallurgical phenomena. Four types of single junction commercial modules were subjected to 140 C testing, both in the dark and under illuminated conditions. The before and after electrical characteristics of individual cells were measured and compared and correlated with physical evidence. A fifth module type could not be tested because of poor adherence of the films to the glass superstrate. A short term effect of stressing was noted which dramatically improved cells with low Voc on one type of construction. All cells eventually showed long term irreversible degradation, but the time to 50% Pm reduction varied by as much as two orders of magnitude depending on construction. No basic difference could be detected between degradation under illuminated or non-illuminated conditions, when cells were either open or short circuited. Comparison with one type of tandem cell and with published results of Japanese cell testing indicated the marked superiority of the tandem cell to all other types. Cells were examined physically by optical, IR, and scanning electron microscopy and by Auger spectroscopy, spectroscopy, secondary ion mass spectroscopy, and energy dispersive x-ray analysis. The long term degradation was felt to be due to localized penetration of aluminum through the amorphous film. (ERA citation 11:055947)