Reverse I-V characteristics of GaAs cells

Abstract

Some GaAs solar cells degrade when exposed to high reverse currents. The degradation is significantly reduced when G e substrates are used instead of GaAs substrates for MOCVD growth of the GaAs cell layers. We compare the performance of GaAs/GaAs and GaAs/Ge cells before and after reverse current stress testing. Diode measurements (dark and illuminated), infrared thermography and crystal defect delineation were used to analyze the cell performance. A three-dimensional computer model for temperature distribution with the cells during testing added insight. The possible effect of the conclusions on advanced GaAs cell design is discussed. BACKGROUND

Study of the reverse I–V in component subcells of III–V multijunction space solar cells

“…In this case, the shadowed device could be forced to operate under reverse bias, possibly near the breakdown region, multiplying its current exponentially. [5] This may result in a catastrophic failure, even affecting the whole array in the worst case. In order to prevent this from occurring, bypass diodes are connected to every solar cell in the array.…”

“…In fact, there are very few studies on the analysis of reverse bias on multijunction solar cells and information about the precise effects that this type of stress has on each subcell is still scarce, being the exact causes for this degradation yet to be understood. [5][6][7][8] Also, several operational situations of multijunction solar cells can force one or more of the subcells to operate in reverse. In addition, the subcell under reverse bias can change during the life of the cell in space.…”

“…This type of damage could occur, for example, when a solar cell in the array gets partially or totally shaded. In this case, the shadowed device could be forced to operate under reverse bias, possibly near the breakdown region, multiplying its current exponentially 5 . This may result in a catastrophic failure, even affecting the whole array in the worst case.…”

GaAs/Ge Solar Powered Aircraft, 1998

“…the data shows that the current is very consistent. Reverse breakdown characteristics of the cells have been studied by Iles et al [5] and the results indicate that GaAs/Ge is more robust then GaAs/GaAs with respect to the amount of reverse current the cells can handle. These tests have showr that proper screening can eliminate this problem.…”

High-efficiency GaAs solar cells grown on passive-Ge substrates by atmospheric pressure OMVPE

“…power-to-weight ratio,GaAs on Ge can outperform GaAs on GaAs solar cells in space applications. Furthermore, the reverse breakdown voltage of GaAs cells grown on Ge substrates is lower than that of GaAs cells grown on GaAs substrates, which can reduce the cell degradation caused by large reverse currents (7). High efficiency GaAs solar cells previously have been demonstrated on passive-Ge substrates(3); however, the detailed growth conditions for control of the GaAs/Ge interface properties were not reported.…”