Investigation of reliability attributes and accelerated stress factors of terrestrial solar cells. Second quarterly report, March 9, 1978--June 9, 1978

The objective of this study is to perform investigations of factors involved in the reliability of terrestrial solar cells and to develop specifications for an Accelerated Stress Testing Schedule for solar cells. Very little was known prior to this program concerning the nature of the time-to-failure (TTF) distributions of solar cells in terrestrial ambient conditions, the failure modes and failure mechanisms which control the TTF distributions, the appropriate methods for accelerated stress testing for reliability verification, or technology verification or the process modifications which might be required to upgrade reliability performance. The program reported represents a first attempt to define these reliability attributes for individual, unencapsulated terrestrial solar cell devices. The program is intended not merely to establish the base-line reliability characteristics for present state-of-the-art cells, but to also establish methodology to both permit intercomparison of available cells and permit evaluation of cell structures which will be developed in the future. Results are presented including (1) establishment of a cell electrical measurement capability with repeatability of better than +-1% (2) progress on stress testing and measurement and (3) design and progress on fabrication of jigs and fixturing for stress testing. Considerable progress was made toward prestress electrical measurement of cellmore » test populations. Delivery was taken of the final items of stress test equipment.« less