Thermal Degradation Mechanisms in GaAs Solar Cells with High-Temperature Contacts.

摘要

This objective of this work was to characterize the thermal stability of GaAs solar cells with high-temperature contacts. High-temperature stability is important for threat environments in space, for compatibility with high-temperature assembly techniques, and for enhanced reliability of cells. Our contact system, described previously, relies on a Pt solid-phase ohmic contact, a TiN barrier layer, and an Au conductor, with contact to a heavily doped p-GaAs contact layer. The behavior of both flat-plate and concentrator cells has been characterized as a function of temperature (400-600 C) and time (5-15 minutes) of the anneal. We find that GaAs cells experience minimal electrical degradation up to 550 C for 5 minutes, or to 490 C for 15 minutes. Increases in the 2kT perimeter dark current are responsible for small decreases in Voc and FF up to these temperatures. At higher temperatures a drastic decrease in efficiency is caused by metallurgical reactions at isolated regions along the grid lines. The reaction, which appears to involve Au-Ga, is initiated at the edges of the grid lines. Away from edges, the contacts are metallurgically stable to at least 600 C. 4 refs., 8 figs., 4 tabs. (ERA citation 14:002915)