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Benchmark and irradiation tests of terrestrial solar cells for low cost space solar array
Sophie Duzellier, Romain Cariou, Thierry Nuns, Philippe Voarino, Fabien Chabuel, Corinne Aicardi
To cite this version:
Sophie Duzellier, Romain Cariou, Thierry Nuns, Philippe Voarino, Fabien Chabuel, et al.. Benchmark
and irradiation tests of terrestrial solar cells for low cost space solar array. EU PVSEC 2020, Sep 2020,
Lisbonne, Portugal. �hal-02955735�
BENCHMARK AND IRRADIATION TES TS OF TERRES TRIAL S OLAR CELLS FOR LOW COS T S PACE S OLAR ARRAY
Sophie DUZELLIER*
ONERA/DPHY, Université de Toulouse F-31055 Toulouse – France
Romain CARIOU Univ. Grenoble Alpes, CEA, LITEN,
DTS, LMPI, F-38000 Grenoble [email protected]
Thierry NUNS
ONERA/DPHY, Université de Toulouse F-31055 Toulouse – France
Philippe VOARINO Univ. Grenoble Alpes, CEA, LITEN,
DTS, LMPI, F-38000 Grenoble [email protected]
Fabien CHABUEL Univ. Grenoble Alpes, CEA, LITEN,
DTS, LMPI, F-38000 Grenoble [email protected]
Corinne AICARDI CNES
F-31400 Toulouse, France [email protected] Abstract — The need for low cost photovoltaic solutions is becoming more and more important with the ongoing NewSpace revolution. In this study, we review, as comprehensively as possible, the radiation hardness of various photovoltaic solar cells technologies. Emphasis is placed on cells offering attractive cost reduction compared to standard III-V based triple junctions.
In addition, the following benchmarking criteria were identified: performance, including begin and end of life evolution (BOL/EOL) when submitted to doses/fluences, mass, Technological Readiness Level (TRL) and reliability.
Keywords — Solar Cells, Irradiations, Electrons, Space Applications.
1. INTRODUCTION
A wind of change is blowing in the space sector. New orbit configurations are foreseen with, for instance, more and more spacecraft using electric propulsion to reach Geostationary Earth Orbit (GEO) [1]. While this propulsion mode allows to save mass and allow thus more payloads, its main drawback is the much larger amount of time in the Geostationary Transfer Orbit (GTO) with prolonged exposure of solar arrays to electrons and protons of radiation belts [2]. Solar electrical propulsion consequently requires to address key photovoltaic (PV) metrics (end of life (EOL) power, W/m2, W/m3, mass, flexible arrays, etc.) for high power systems.
Other important NewSpace [3] trends are the mega-constellations and low-cost missions, shaking up the traditional approach by using Components Off the Shelves (COTS) and high volume production manufacturing lines. Those trends are driving low cost solar arrays innovations.
Historically, silicon solar cells were developed together with space applications since their first use on Vanguard 1 in 1958.
However, in 1990s, the GaAs/Ge followed by GaInP/GaAs/Ge multi-junction solar cells gradually replaced silicon for their high efficiency and high resistance to space radiation (electrons & protons) [4]. Thus, the current state of practice in space PV is to use optimized monolithic triple junction (3J) solar cells that combine several layers of III-V materials, to convert a broad part of AM 0 solar spectrum [5]. Those type of solar cells typically have AM 0 efficiency around 30% in 3J configuration and even 32% in 4-junction (4J) configuration [6]. Their main drawback lies in their prices, roughly 2-3 orders of magnitude higher than a standard terrestrial silicon cell for instance; in addition, the Ge substrates used commonly for III-V cells, with a thickness in the 150µm range, are also relatively massive.
On the other hand, some terrestrial technologies have shown these last years significant performances improvements, exceeding efficiencies of more than 20%.
In this context, terrestrial solar cells are potential good candidates to address the cost and/or mass challenge, provided their performances and response to space radiations are acceptable and compatible with mission requirements. This paper provides a review on a set of terrestrial solar technologies. A radiation benchmark based on pertinent test approach is defined to evaluate state of the art terrestrial cell technologies (commercial or pre-commercial) such as perovskite (Pk) and silicon. The aim is to conclude on their capabilities to fly in a realistic space mission configuration (LEO, GEO, flexible arrays, etc.).
2. SOLAR CELLS REVIEWS 2.1 State of the art technologies
Laboratory efficiency records for solar cells are listed in the biannual publication from Green et al. [7]. III-V cells, as mentioned previously, are leading the efficiency race with record efficiencies of 47.1% for a 6-junction device under concentrated AM 1.5d spectrum, 39.2% for a six junctions under AM 1.5g spectrum, and more than 35% for a 4J device under AM 0 spectrum [8].
M ore interestingly for this study, other technologies (with lower efficiency though) have a strong potential in terms of mass and/or cost savings. This is the case for instance for c-Si and perovskite solar cells. Perovskites, with an absorber thickness in the few hundreds nm range, can bring significant mass saving; in addition, Pk cells are reaching 25.2% (0.1cm2).
Concerning c-Si, Kaneka holds record power conversion efficiency with 26.7% AM1.5G spectrum, for a 80 cm2 IBC cells.
Those lab efficiencies give indication of technology potential, but available commercial products have lower efficiency and may require developments for space compatibility (e.g. substrate, size, architecture, etc.).
2.2 Solar Cells Radiation Hardness
Solar cells, as opto-electronic devices, are susceptible to damage dose induced by the radiative space environment. The interaction mechanisms with electrons and protons produce displacement defects (points defects such as vacancies and intertistials, Frenkel pairs, complex defects) acting as recombination centers. The result is a reduced carrier lifetime and diffusion length, which impacts on cells performances.
Radiation data on thin films solar cells technologies are reported in the literature from decades [9]-[17][21]. Bätzner et al.
in 2004 provided a comparison between different technologies (Figure 1) based on the displacement damage formalism (fluence multiplied by material specific Non-Ionizing Energy Loss parameter).
Figure 1: Electrons/Protons degradation curves for different technologies [14]. Efficiency remaining factor (RF) versus damage dose
Pk cells are also resistant to electrons and protons showing great stability [15][16]. It appears that this resistance is mostly due to rapid self-annealing mechanisms temperature-dependent [17]. Organic nature of Pk suggests ionization also plays a major role here inducing scissions of covalent links such as C-H and N-H, freeing H atoms contributing to the formation of recombination centers in the bandgap of the bulk material, but also passivating intrinsic or radiation defects.
To conclude here, common trends in radiation response of Pk and also some thin films technologies are:
• Stable response up to large 1M eV electron fluence (1016-1018 #/cm²)
• Degradation with low energy protons (50-300keV, fluence >1012-1013 #/cm²) when peak of damage is localized near junction and interfaces
• Self-healing mechanisms leading to partial or complete annealing (thermally and photo stimulated)
3. RADIATIONS TEST PLAN 3.1 Radiation Test Approach
Radiation testing of samples (electronics) requires adequate configuration depending on radiation species:
• Electrons are penetrating particles with constant dose deposition with target depth but able to induce charging of dielectrics or insulating materials and inducing overheating of samples when large beam current is used during irradiation (large flux).
• Protons range strongly depends on energy and mode of interaction; it leads to limited range and non-uniform dose profile with maximum of interaction at the end of the track (Bragg peak).
In case of solar cells (not shielded from radiation) representative energy ranges in a typical LEO-to-GEO space environment are 10-30M eV for electrons (few mm penetration depth) and 1-10M eV with protons (few tens of µm).
Therefore, electrons can be easily used for irradiating solar cell assemblies (SCA i.e. with coverglass or encapsulation) whereas irradiating with low energy protons (the most “damaging”) required bare solar cells (or ultra-thin encapsulation layers).
Regarding representativeness, solar cell on-board solar generator systems (SGS) are exposed to combined electron/proton with space flux defining the degradation/recovery kinetic ratio.
Technical limitations at accelerators forbid the irradiation on earth at space flux (much too low) and usual acceleration factors typically lie in the 103-105 range. The expected space degradation/recovery ratio can thus not be simulated at ground.
However, in-situ testing may overcome this difficulty by allowing annealing monitoring and more testing at incremental steps of fluence under vacuum.
Therefore, the test plan (see Figure 2) includes electron irradiation, in-situ dark and light I(V) at M IRAGE facility (Axel Lab. [20][19]), as well as ex-situ complete caracterisations at CEA-LITEN, for both commercial Si and Pk cells .
Figure 2: Test sequence with dark and light I(V) steps (DIV and LIV) 3.2 Cells and Constraints
As mentioned above, two commercial technologies are selected for this first campaign: perovskite modules (few tens of cm2), terrestrial silicon solar cells (few cm2 cuts from large cells).
For each of these technologies, sample configuration is not adequate for space application and thus for radiation testing.
For instance, the Pk samples are encapsulated; therefore, it forbids any low energy protons testing (limited penetration depth).
Temperature is also a critical parameter for the cells electrical performance and radiation response. Therefore, typical irradiation set-up includes thermal regulation of samples through backside contact with cooled/heated plate.
Again the flexible/encapsulated Pk sample does not allow good thermal contact with backside plate; in addition, polymer materials are well known to degrade under radiation with the formation of color centers. Thus Pk encapsulation degradation will limit the analysis of radiation data introducing absorption bands in LIV testing.
Regarding sample size, typical beams spot is limited (flux non-uniformity monitored on 14x14cm² here) i.e. large devices cannot be fully exposed at once and the need for data with good statistics implies cutting large coupons into several small ones for testing (Si cells).
4. EXPERIM ENTAL RESULTS
Irradiation test campaigns have been shortened due to the COVID19 lock down period, thus only limited 1M eV electron irradiation on Pk and Si cells could be performed so far. 1M eV electron testing is recommended by the standards and norms (equivalent fluence concept).
Next table details the irradiation and in-situ testing steps. During this electron test campaign, short and medium-term annealing at RT was also investigated. In-situ DIV/LIV (1AM 0) was performed at each step.
Table I: The different steps of the 1M eV electron test campaign
Next figure provides LIV curves for Pk module measured ex-situ under AM 0 spectrum in begin-of-life (BOL) and end- of-life (EOL), here 6.8 1015 e-/cm2.
As one can see, the degradation of the Jsc is significant, while the Voc does not degrade and is even improved after completing the irradiation through self-annealing mechanism.
Figure 3: Ex-situ Light I(V) @AM 0 of Pk modules (107D sample) in BOL and EOL (6.8 1015 1M eV e-/cm2). Note that the Pk was irradiated with its terrestrial encapsulation
The origin of the Jsc degradation is at least partially related to the transmittance degradation of the polymer/barrier layers encapsulating: this hypothesis was verified through BOL/EOL measurements on independent polymer / barrier films, as shown in Figure 4.
Figure 4: Degradation of transmittance in % of PK encapulation films due to 1M eV electrons. Increased absorption with increasing fluence in the visible range.
Absorption in visible wavelength is linked to scission/cross-linking of polymer chain (double-bonds creation) leading to formation of color centers (Fig.4). It induces yellowing of the materials, whereas cross linking induces stiffening of the encapsulation until mechanical deformation.
Figure 5 shows evidence of rapid self-annealing occurring within few minutes after the end of irradiation. This observation confirms what is reported in [11] and explains the great stability of Pk to radiation. Only in-situ measurements allow for monitoring such rapid self-annealing.
Figure 5: Self-annealing at room temperature under vacuum after the end of irradiation (fluence 6.8 1015 1M eV electrons/cm², 107D sample)
The Silicon in-situ Ligth IV measurements on sample A1 are disclosed in Figure 6 below. Both Isc and Voc are gradually affected by radiation (FF is stable) and no short-term annealing is observed.
The evolution of main parameters with fluence shows that Pm ax degradation curve is “driven” by Isc evolution (Figure 7).
40 50 60 70 80 90 100
0 10 20 30 40 50 60 70 80 90 100
0 500 1000 1500 2000 2500 3000
% Transmittance
Wavelength nm
barrier foil
PET/ITO 3 steps (1MeV electron)
*init
*fluence 1E15
*fluence 6.8E15
Figure 6: Light I(V) measurements in-situ during each electron irradiation steps on commercial terrestrial silicon cells (A1 Si sample)
Figure 7: Evolution of RF for Isc, Voc, Pmax and FF parameters with fluence (A1 Si sample)
With uniform degradation in the cell bulk induced by electrons, EQE data from Fig.8 suggest lower collection for rear side carriers (longer wavelength affected). Finally the Jsc remaining factor is 67% at total fluence of 5 1015 e-/cm².
Figure 8: EQE data on A3 Si sample (EOL ex-situ characterization)
Figure 9 provides RF(Voc) comparison for 1M eV electron fluence between benchmark samples and “space” technologies.
Firstly, comparing RF(Voc) for PK and Si samples, it is interesting to observe that PK sample starts degrading at much higher fluence (>>1015 #/cm²) but exhibits Voc drop of similar amplitude at total fluence.
-5,E-01 -4,E-01 -3,E-01 -2,E-01 -1,E-01 0,E+00 1,E-01 2,E-01 3,E-01 4,E-01
-0,1 0,1 0,3 0,5 0,7
Current (A)
Voltage (V) Si A1 (1MeV electron)
BOL vaccum 2E135E13 1E141E15 1E15 +15h 5E155E15 +15h
Figure 9: Comparison of RF(Voc) for PK and Si samples with “conventional” space technologies (radiation figures from product datasheets). Typical equivalent fluence are shown for LEO, GEO and M EO orbits.
Secondly, benchmark radiation data clearly show that no optimized Si technology still exhibits acceptable EOL RF(Voc) while the “extreme” resistance to radiation of PK technology is confirmed to be due to self-healing mechanisms.
Lastly, it is very likely that on-board spacecraft (electron orbit) no degradation at all would be observed on Pk due to the much lower flux in orbit leading to real-time/concurrent compensation of degradation by self-annealing (similar kinetics of mechanisms).
5. CONCLUSIONS AND PERSPECTIVES
This work is a first step to determine the viability of terrestrial solar cells in a space radiative environment.
1M eV electron testing have been performed on commercial Pk modules and Si cuts showing great stability of Pk due to self-annealing mechanisms and gradual degradation of Si samples with fluence. M ore testing (with protons, or combined protons/electrons) is planned to complete this study.
This benchmark will be the basis for ranking of technologies relatively to typical orbits and mission and the opportunity to define further investigation on most promising cells (understanding of degradation mechanisms, recommendations for flight operation conditions…).
6. ACKNOWLEDGM ENT
This work has been supported by the Centre National d’Etudes Spatiales (CNES).
7. REFERENCES
[1] G.A. Landis, S.R. Oleson, and C.R. M ercer, in 2015 IEEE 42nd Photovolt. Spec. Conf. PVSC (IEEE, New Orleans, LA, 2015), pp. 1–4.
[2] R. M aurer, J. Goldsten, P. Peplowski, A. Holmes-Siedle, M . Butler, C. Herrmann, and B. M auk, IEEE Trans. Nucl. Sci.
60, 4053 (2013).
[3] J.N. Pelton, Space 2.0: Revolutionary Advances in the Space Industry (2019).
[4] P.A. Iles, Sol. Energy M ater. Sol. Cells 68, 1 (2001).
[5] C.A. Gueymard, Sol. Energy 169, 434 (2018).
[6] W. Guter, F. Dunzer, L. Ebel, K. Hillerich, W. Köstler, T. Kubera, M . M eusel, B. Postels, and C. Wächter, E3S Web Conf. 16, 03005 (2017).
[7] M .A. Green, E.D. Dunlop, J. Hohl‐Ebinger, M . Yoshita, N. Kopidakis, and A.W.Y. Ho‐Baillie, Prog. Photovolt. Res.
Appl. 28, 3 (2020).
[8] G. Siefer, in 2019 Eur. Space Power Conf. ESPC (n.d.).
[9] Y. Hirose, M . Warasawa, K. Takakura, S. Kimura, S.F. Chichibu, H. Ohyama, M . Sugiyama, “Optical and electrical properties of electron-irradiated Cu(In,Ga)Se2 solar cells”, Thin Solid Films 519 (2011) 7321–7323.
[10] A. Jasenek and U. Rau, ‘Defect generation in Cu(In,Ga)Se2 heterojunction solar cells by high-energy electron and proton irradiation’, J. Appl. Phys., vol. 90, no. 2, pp. 650–658, Jul. 2001.
[11] S.Kawakita et al., ‘In-situ measurement of degradation of Cu(In,Ga)Se/sub 2/ thin film solar cells during electron and proton irradiations’, in Conference Record of the Twenty-Ninth IEEE Photovoltaic Specialists Conference, 2002., New Orleans, LA, USA, 2002, pp. 978–981.
[12] K. Weinert, M . Schwicken, and U. Rau, ‘Irradiation of Cu(In,Ga)Se2 thin film solar cells with 110-, 210-, and 290- keV protons’, in Proceedings of 3rd World Conference on Photovoltaic Energy Conversion, Osaka, Japan, 2003, pp. 697–
700.
[13] D. A. Lamb et al., ‘Proton irradiation of CdTe thin film photovoltaics deposited on cerium-doped space glass’, Prog.
Photovolt. Res. Appl., vol. 25, no. 12, pp. 1059–1067, Dec. 2017.
[14] D. L. Bätzner, A. Romeo, M . Terheggen, M . Döbeli, H. Zogg, and A. N. Tiwari, ‘Stability aspects in CdTe/CdS solar cells’, Thin Solid Films, vol. 451–452, pp. 536–543, M ar. 2004.
0,600,65 0,700,75 0,800,85 0,900,95 1,001,05
1,0E+13 1,0E+14 1,0E+15 1,0E+16
RF(Voc)
1MeV electron fluence benchmark vs commercial cells (space)
Si Benchmark PK benchmark Si Azur Space S32 3J 3G30C Azur Space Z4J Solaero
self- annealing LEO GEO MEO
[15] Y. M iyazawa, M . Ikegami, T. M iyasaka, T. Ohshima, M . Imaizumi, and K. Hirose, ‘Evaluation of radiation tolerance of perovskite solar cell for use in space’, in 2015 IEEE 42nd Photovoltaic Specialist Conference (PVSC), New Orleans, 2015, pp. 1–4.
[16] F. Lang et al., ‘Radiation Hardness and Self-Healing of Perovskite Solar Cells’, Advanced Materials, vol. 28, no. 39, pp.
8726–8731, Oct. 2016, doi: 10.1002/adma.201603326.
[17] V.V. Brus et al., ‘Defect Dynamics in Proton Irradiated CH3NH3PbI3 Perovskite Solar Cells’, Advanced Electronic M aterials, vol. 3, no. 2, p. 1600438, Feb. 2017, doi: 10.1002/aelm.201600438.
[18] J.-S. Huang et al., ‘Effects of Electron and Proton Radiation on Perovskite Solar Cells for Space Solar Power Application’, in 2017 IEEE 44th Photovoltaic Specialist Conference (PVSC), Washington, DC, 2017, pp. 1248–1252.
[19] A. Sicard et al., “GREEN: the new Global Radiation Earth Environment model”, Ann. GeoPhys. 36, 953-967, 2018.
[20] S. Duzellier, T. Nuns, J.P. David, C. Pons, R. Rey, C. Cavel, G. Chanteperdrix, " Evaluation of tri-junction solar cells response to electrons and protons of the JUICE specific environment", WCPEC conference 2001
[21] T. Ohshima et al., ‘M echanis m of anomalous degradation of silicon solar cells subjected to high-fluence irradiation’, IEEE Trans. Nucl. Sci., vol. 43, no. 6, pp. 2990–2997, 1996.
[22] O. M alinkiewicz et al., “Radiation Effects on the Performance of Flexible Perovskite Solar Celles for Space Application”, https://doi.org/10.1007/s42247-020-00071-8 (Springer 2020).
