Impact on devices and degradation of solar cells

 

Space radiation strongly influences the technology on board the spacecraft and the solar cells that power it. In case of extreme events, radiation incident on electronics can cause permanent defects in the devices, degrading their performance. Common adverse Space Weather effects on spacecraft/satellite are the erroneous signals in the electronics caused by radiation passing through the shielding and spacecraft charging, i.e. the phenomenon by which the accumulation of electrostatic charge on the spacecraft's surface finally causes sudden discharges, which again lead to erroneous signals in the electronics. A main problem is the degradation of the performance of solar cells. Solar cells are a fundamental component of Space probes, as they are needed to generate the required power for guidance, navigation, control, instrumentation, thermal control, communications, data handling, and many other subsystems. Trapped radiation, solar protons and GCRs create atomic defects in the materials constituting the solar cells, by displacing atoms, and they modify the electronic current, reducing the solar cell power output.

At present, the most efficient solar cells currently in production are multi-junction solar cells, which use a combination of several layers of GaAs, GaInP and Ge to capture more energy from the solar spectrum [1,2]. The band gap obviously determine the energy at which the absorption generally starts. Space solar cells are protected by a cover glass (made by cerium oxide), which mostly slows down the whole proton spectrum and high energy particles. According to the overall damage, the solar cell output (short-circuit current, open-circuit voltage, output power) is reduced.

The major type of radiation damage in space solar cells are ionization (mainly for the coverglass material) and atomic displacement (for the cell itself) due to high energy protons and electrons (although, low-energy protons can also cause problems). Ionizing radiation can reduce the transmittance of the solar cover glasses through the development of color centers in the oxide: these occur when electrons excited by the radiation become trapped by impurity atoms in the oxide to form stable defect complexes. Thick cover glasses protect the cell from the highly damaging low-energy protons, but also induce a relevant decrease in the power of the solar cell. Such decrease can be limited by using concentrators design [3,4].

 

[1] M. Meyer, R. A. Metzger, Flying High, Compound Semiconductor, Special Issue, 40 (1997).

[2] T. Torchynska, G. Polupan, F. C. Zelocuatecatl, E. Scherbina, Modern Phys. Lett. 15, 593 (2001).

[3] S. Bailey and R. Raffaelle, Space Solar Cells and Arrays, in Handbook of Photovoltaic Science and Engineering, Edited by A. Luque and D. Hegedus, 2003, John Wiley and Sons, Ltd.

[4] A. De Luca, Architectural design criteria for spacecraft solar arrays.INTECH Open Access Publish (2011).

 

 

 

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