Triple Junction By-Pass Diode Characterization and Testing

The design and qualification of a reliable shunt diode device is of primary importance for all the solar array programs using GaAs triple junction (TJ) solar cells. Main issues are the sensitivity of cells to reverse bias application and their particular behaviour under reverse conditions (interaction between illumination and junction biasing). These matters impose a strong and reliable protection for every solar cell that can be implemented by means of integral diode concept. In the recent past, few diode anomalous behaviours have been detected during long duration high temperature testing: they were caused by marginal design but also by external causes like voltage and current spikes, not really representative of in-orbit conditions. Starting from these "negative" experiences, we first improved the integral diode design and then we verified by means of a comprehensive campaign all the major technical issues: on-ground and in-orbit spike environment, component rating with respect to the diode, solar cell electrical characteristics were therefore investigated and a qualification plan based on this approach was established covering all the aspects. This paper presents the diode lifetime analysis focused on spikes generator, the derating rules and finally describes all the characterization and testing activities performed for qualifying the integral by-pass device.