Carsten Baur

External quantum efficiency measurements of Germanium bottom subcells: Measurement artifacts and correction procedures

The measurement procedures for the determination of the external quantum efficiency (EQE) of individual subcells in a monolithic, series connected stack of solar cells are known since the 1980s [1]. There, the importance of the choice of appropriate bias light spectrum and bias voltage was already addressed. However, especially when measuring the EQE of Germanium bottom subcells in monolithic III–V triple-junction cells artifacts in the measured EQE are frequently found. Such an artifact can be identified by concurrent observation of a significant parasitic EQE signal in the wavelength region of another subcell — in the majority of the cases in the response region of the middle subcell - AND a comparatively lowly determined EQE of the subcell intended to be measured — usually the Germanium bottom subcell. A procedure how to correct such an EQE measurement that shows an artifact is introduced in [2]. However, only a procedure correcting for the parasitic EQE signal in the response region of the subcell which is not under test, is given. In this paper we will present an additional correction procedure that also corrects for the too lowly measured EQE of the subcell under test.

Measurements of the Flashover Expansion on a Real-Solar Panel—Preliminary Results of EMAGS3 Project

When a primary discharge occurs on a solar array, it is important to understand what would be the maximum flashover expansion. This value would then be representative of in-flight scenarios on full panel size. This paper presents the results of the experimental campaign performed in the frame of the European Space Agency EMAGS3 project “Flash-over evaluation on large solar panels” and where we measure flashovers in different conditions on a real-solar panel. This experimental campaign is conducted in the large vacuum chamber of Industrieanlagen-Betriebsgesellschaft mbH (IABG) (Germany) on a solar panel of 4 × 2 m provided by Astrium-Germany and organized in 52 linear strings of silicon cells covered by Cerium doped borosilicate glass (CMX) coverglasses (CG). During the test, several parameters are studied such as inverted potential gradient (IPG) obtained in plasma or in electrons and test of flashover expansion over a gap between panels by addition of a small panel. The main difficulty is in the evaluation of the value and homogeneity of the initial potential gradient to be able to determine the initial stored charge. The development of a model of flashover expansion has contributed significantly to the comprehension of the results and the assessment of the initial stored charge. During the first step (IPG by electrons at room temperature) ~ 200 electrostatic discharges (ESDs) are recorded of which 12 discharge of the theoretical stored charge in the CG. In IPG by plasma at room temperature, ~ 100 ESDs are recorded, 12 discharging of the theoretical stored charge including two that discharged the panel completely. With this test campaign we demonstrate that, even if the probability is not very high, an ESD on a solar panel could lead a flashover to expand and neutralize the complete surface of an 8- m2 panel. In addition, we see that the flashover can continue across a gap of 10 cm.

The Influence of High Temperatures on Radiation Damage of GaInP

We report on the isothermal annealing behavior of 1 MeV electron irradiated component cells of a GaInP2/GaAs/Ge triple-junction solar cell. The defect concentration as a function of annealing time and temperature is derived from the in situ measured open-circuit voltages. The time-dependent behavior reveals the presence of partly overlapping exponential decays in defect concentration that, in turn, suggests the annealing of more than one defect having different activation energies.

_{\bf 2}

Latest results of 3G28 triple-junction solar cells manufactured by AZUR SPACE Solar Power GmbH under low intensity low temperature (LILT) conditions are reported. Excellent beginning of life (BOL) efficiencies in the order of 35% at 50W/m2 and -150°C have been realized on a large number of cells with standard and LILT optimized design. Furthermore, temperature dependent irradiation tests with 1 MeV electrons and 1 MeV protons have been performed on LILT optimized 3G28 solar cells. Initial results show some indications of temperature annealing but also other stabilization effects already present at LILT conditions.

/GaAs/Ge Triple Junction Cells

The paper reports about the possibility of predicting the degradation of III–V multi-junction solar cells due to particle irradiation in space solely based on the radiation response of the respective sub cells. State-of-the art triple-junction solar cells of the 3G28 class manufactured by AZUR Space GmbH are used as an example to demonstrate how to model the degradation behavior of multi-junction cell from the degradation behavior of the respective component cells, as investigated in this study. The advantages of component cells for understanding and modeling the behavior of multi-junction cells under different conditions are discussed.

Development status of triple-junction solar cells optimized for low intensity low temperature applications

This paper first presents a short review of the recent experiments performed on large test fixtures, whose aim was to evaluate the flashover (FO) propagation during an electrostatic discharge. Then, the model of plasma bubble expansion is presented and compared with the results collected during the review. We will show that the model can represent qualitatively and quantitatively most of the results. The parameters of the model are mainly the ion velocity and the backscattered electron emission yield. The other experimental parameters influencing the FO propagation will be discussed.

Modeling of the degradation of III–V triple-junction cells due to particle irradiation on the basis of component cells

We report on the angular dependence (0° to 86°) of the current and voltage behavior of GaInP2/GaAs/Ge triple-junction cells and corresponding GaInP2 and GaAs component cells. Thereby, additional parameters such as temperature, cover glassing, degradation due to particle irradiation and subsequent annealing have been varied and their impact on the angular dependence has been assessed. The current limiting subcell of the triple-junction cell has been identified in each case and special focus has been put to the question whether a change of the current limitation from the GaInP2 top cell to the GaAs middle cell can happen in some cases simply because of the light entering the cell at a higher inclination angle. The validity of the one diode model when measuring the solar cell under various angles has been verified analyzing respective open circuit voltage-short circuit current pairs.

Influence of Different Parameters on Flashover Propagation on a Solar Panel

Space solar arrays come in all different shapes and sizes, engineered to cope with environments ranging from the low intensity low temperature (LILT) of deep space missions, to the high intensity high temperature (HIHT) environments of near sun probes. This paper provides a guided tour of a range of solar arrays that the European Space Agency (ESA) has recently, or is currently developing, in collaboration with European industry.

The influence of high light inclination angles on the performance of GaInP 2 /GaAs/Ge triple junction solar cells

In this paper spectral response measurements at low intensity and low - high cell temperature ranging from -160°C (113 K) and +197°C (470 K) on a monolithic lattice-matched triple junction GaAs solar cell are presented. Apart from the present SR measurement set-up utilized at SPASOLAB for ambient cell temperature, a cryostat chamber has been built up to set the temperature of the testing cell device to this low-high temperature range. Results in units of external quantum efficiency of each subcell of this triple junction cell are given and compared with available information of previous studies. This system up-grading forms part of the Aurora-ExoMars program by the European Space Agency (ESA).

From LILT to HIHT and everything in between

Currently ESA is considering a variety of missions which extend from extreme near-sun environment at Mercury out to Jupiter and beyond. These missions impose dramatically different environments (illumination intensity, operating temperature, particle radiation). This paper will discuss the challenges for solar array technology.