GaAs single junction cells, representative of the middle cell in triple junction Ga 0.5 In 0.5 P/GaAs/Ge cells, were irradiated with various fluences of 1-and 3-MeV electrons as well as 1-MeV protons.The light I-V curves measured at room temperature exhibit a voltage-dependent photocurrent.The photocurrent is modeled taking into account the voltage-dependent width of the space charge region in combination with a strongly decreased minority carrier diffusion length. By extracting the width of the space charge region from capacitance measurements and the base layer diffusion length from the external quantum efficiency of the cell, the experimental behavior is reproduced accurately.

Characteristic degradation curves for proton and electron induced degradation of triple junction (3J) and isotype Ga0.5In0.5P/GaAs/Ge solar cells were obtained. The displacement damage dose methodology in combination with a varying effective threshold energy for atomic displacement Td,eff was used to analyze 3G28 and 3G30 3J cell data. The nonionizing energy loss (NIEL) was calculated analytically, and Td,eff was explicitly introduced as a fit parameter. Using the GaAs NIEL in fitting the 3J degradation data, a Td,eff of 21 eV was determined, whereas a Td,eff of 36 eV was found using the Ga0.5In0.5P NIEL. In GaAs and Ga0.5In0.5P single junction cells, the effective threshold energies for atomic displacement of 22 and 34 eV were determined. Copyright © 2017 John Wiley & Sons, Ltd.

The behavior of standard space photovoltaic assemblies in a high intensity, high temperature environment (HIHT) is addressed. Experimentally, an HIHT environment, typical for missions to the inner planets of the solar system such as Mercury, characterized by temperatures of 500K and 11 solar constant irradiance in the ultraviolet region below 400 nm, was simulated in a vacuum. Independently of the triple junction cell technology used, module degradation up to 20% in power was observed during several hundred hours of test. Electroluminescence analysis identified discrete top cell shunts close to the cell edge, in particular around the frontside contact pads. Cross‐sectional transmission electron microscopy performed on several degraded cells revealed an etched contact pad metallization/cap layer interface and more importantly, several 100‐nm large, oriented Cu3P inclusions at the shunted locations. A chemical degradation mechanism is proposed. Short wavelength ultraviolet light interacting with polysiloxanes used as module encapsulant produces hydrogen and methyl radicals. With these building blocks, an organic acid can be formed on external reaction surfaces such as the Ag busbars that simultaneously serve as a source of oxygen. Cu traces present in the Ag segregate to the surface and are transported by this acid to the contact pad of the cell in the liquid phase. An adapted cell design was developed to prevent this degradation mechanism believed to be of relevance for all HIHT space environments. A several hundred micrometer‐wide rim composed of the outermost cell area is electrically separated from the inner cell area and provides a barrier against environmental attack. None of the photovoltaic assemblies featuring this mesa cell design showed any fill factor‐induced power degradation any more. Copyright © 2011 John Wiley & Sons, Ltd.

BepiColombo is the joint mission of the European Space Agency (ESA) and the Japanese Aerospace Exploration Agency (JAXA) to explore the planet mercury. The European contributions, namely the mercury transfer module (MTM) and the mercury planetary orbiter (MPO), are both powered by deployable solar arrays. Many materials and technologies are at their limit under the harsh highintensity, high-temperature (HIHT) conditions of the mission. Synergistic effects like photo fixation and photo enhanced contamination by ultra violet and vacuum ultra violet radiation (UV/VUV) on sunlit surfaces are considered to play an important role in the HIHT environment of the BepiColombo mission. A design verification test under UV/VUV conditions of sun exposed materials and technologies on component level is presented which forms part of the overall verification and qualification of the solar array design of the MTM and MPO. The test concentrates on the selfcontamination aspects and the resulting performance losses of the solar array under high intensity and elevated temperature environment representative for the photovoltaic assembly (PVA).

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