1. Mitsuru Imaizumi Space Solar Cells -- I -- HTV-6
Spacecraft Power System, Kyusyu Inst. Tech Oct. 19, 2018
Space Solar Cells -- I --
HTV-6
Mitsuru Imaizumi

2. Contents Solar cell utilization in space Fundamentals of solar cells
Development history
Radiation degradation
Degradation prediction
Recent R&D activities

3. Contents Solar cell utilization in space Fundamentals of solar cells
Development history
Radiation degradation
Degradation prediction
Recent R&D activities

4. Solar Panels/Paddles
GCOM-W1
GOSAT
WINDS

5. Solar Panels/Paddles
HTV
GMS-5
MMO 5

6. Parallel number: Generation current Layout of solar cells in a panel
Solar Panels/Paddles
Solar Paddle
この表は、ＣＳＤ搭載評価サンプルの名称と個数を示す。
７品種について２個ずつ搭載し、評価を実施している。
打上後の初期チェックアウト時に、各評価デバイスについて電気特性のデータを取得し、
全て正常に機能し、データが得られていることを確認した。
Series number: Generation voltage
Output voltage
Output current
Parallel number: Generation current
Layout of solar cells in a panel 6

7. High efficiency Si solar cell InGaP/GaAs/Ge triple-junction solar cell
Space Solar Cells
Buried bypass diodes
Bypass diode
Interconnector
Cell size: 2×2 cm2
Size: 40mm×60mm
Size: 37mm×76mm
High efficiency Si solar cell
InGaP/GaAs/Ge triple-junction solar cell

8. A coupon solar panel with Si solar cells for testing
Space Solar Panel
Cell size: 2×2 cm2
A coupon solar panel with Si solar cells for testing

9. Structure of Solar Panels
Solar cell
Coverglass
Adhesive
Electrodes
AR coating
Polyimide film
Aluminum Honeycomb
CFRP
Cross-sectional schematic of a solar panel (not to scale)

10. Contents Solar cell utilization in space Fundamentals of solar cells
Development history
Radiation degradation
Degradation prediction
Recent R&D activities

11. Current-Voltage Characteristics
Current-voltage (I-V) characteristics of a solar cell

12. A typical current-voltage (I-V) curve
Output Parameters
A typical current-voltage (I-V) curve

13. Equivalent Circuit of Solar CellsId Vd Rs
= 0
Iph
Rsh
= ∞ V n
= 1
Ish
Equivalent circuit of a (single-junction) solar cell

14. Contents Solar cell utilization in space Fundamentals of solar cells
Development history
Radiation degradation
Degradation prediction
Recent R&D activities

15. High efficiency Si solar cell InGaP/GaAs/Ge triple-junction solar cell
Space Solar Cells
Buried bypass diodes
Bypass diode
Inter-connector
Cell size: 2×2 cm2
Size: 40mm×60mm
Size: 37mm×76mm
High efficiency Si solar cell
InGaP/GaAs/Ge triple-junction solar cell

16. Structure of Si Space Solar Cell
Schematic cross-sectional structure of the “HES” Si space solar cell

17. Back-Surface Field Layer
n-type
Emitter
Depletion
Layer
p-type
Base
n-type
Emitter
Depletion
Layer
p-type
Base
BSF
no BSF layer
with BSF layer
Effect of insertion of the back-surface field (BSF) layer

18. Back-Surface Reflection Layer
Solar Cell
Substrate
Visible light
Infrared (unabsorbed) light
Substrate
BSR
Solar Cell
Visible light
Infrared (unabsorbed) light
no BSR layer
with BSR layer
Effect of insertion of the back-surface reflection (BSR) layer

19. Non-Reflection Surface Structure
Solar Cell
Reflection
ARC
Texture
Solar Cell
ARC
Reflection
Flat surface
Textured surface
Effect of the textured non-reflection surface (NRS) structure

20. Efficiency of Space Solar Cells
Historical improvement of the efficiency of space solar cells

21. High efficiency Si solar cell InGaP/GaAs/Ge triple-junction solar cell
Space Solar Cells
Buried bypass diodes
Bypass diode
Inter-connector
Cell size: 2×2 cm2
Size: 40mm×60mm
Size: 37mm×76mm
High efficiency Si solar cell
InGaP/GaAs/Ge triple-junction solar cell

22. Structure of 3J Space Solar Cell
Cross-sectional structure of an InGaP/GaAs/Ge triple-junction (3J) solar cell

23. Current-Voltage Charateristics of 3J Cell
A typical current-voltage (I-V) characteristics of an InGaP/GaAs/Ge 3J solar cell

24. Efficiency of Space Solar Cells
Historical improvement of the efficiency of space solar cells

25. Effect of Efficiency Improvement
HES solar cell
(η=17%)
3J solar cell
(η=27%)
Area reduction of about 60%
この表は、ＣＳＤ搭載評価サンプルの名称と個数を示す。
７品種について２個ずつ搭載し、評価を実施している。
打上後の初期チェックアウト時に、各評価デバイスについて電気特性のデータを取得し、
全て正常に機能し、データが得られていることを確認した。
Effect of improvement of solar cell efficiency (paddle-size reduction)

26. Contents Solar cell utilization in space Fundamentals of solar cells
Development history
Radiation degradation
Degradation prediction
Recent R&D activities

27. Space Environment for Solar Cells
Radiation (High energy electrons/protons)
High/low temperature and thermal cycles
Ultraviolet
Charging/discharging
Mechanical vibration and sonic wave
Debris/meteoroids (particle)

28. Requirements for Space Solar Cells
Efficiency … but not at BOL but at EOL
Radiation resistance
Lightweight
Thermal (cycle) durability
Mechanical strength
Inexpensiveness

29. Structure of Solar Panel Cross-sectional schematic of a solar panel
Solar cell
Coverglass
Adhesive
Electrodes
AR coating
Polyimide film
Aluminum Honeycomb
CFRP
Cross-sectional schematic of a solar panel

30. Radiation Degradation of Output
High fluence
Cell size: 2×2 cm2
Degradation on I-V characteristics
Beginning-of-life (BOL) and end-of-life (EOL)
Degradation of solar cell output due to radiation exposure

31. Decrease in Output Parameters
Absolute values
Remaining factors
Degradation trend of HES solar cell due to 10 MeV proton irradiation

32. Contents Solar cell utilization in space Fundamentals of solar cells
Development history
Radiation degradation
Degradation prediction
Recent R&D activities

33. Prediction of Radiation Degradation
Difference between ground tests and actual space to be considered
Ground tests
Actual space
Normal incidence
Mono energy
No shielding
Omni-directional incidence (4π)
Multi energy
Shielding effects Front: coverglass Back: substrate

34. Radiation Environment
An example of the chronal change in dose rates of protons and electrons

35. Radiation Environment
An example of the dependency of proton dose rates on proton energy

36. An example of the dependency of degradation curves on proton energy

37. Relative Damage Coefficients
Reference energy
Electrons: 1 MeV Protons: 10MeV
An example of the relative damage coefficients for protons

38. Prediction of Radiation Degradation
Matters to be considered and estimated
Reduction of energy and dose rate due to shielding effect by coverglass etc.
Effective penetration depth depending on incident angle.

39. Equivalent Fluence
Calculation of the equivalent 1 MeV electron fluence
1 MeV electron / 10 MeV proton conversion factor: k
Isc
Voc
Pmax
4350
1280
2580
For HES cell

40. Prediction of Radiation Degradation
An example of estimation of degradation rate from the equivalent 1 MeV electron fluence

41. Contents Solar cell utilization in space Fundamentals of solar cells
Development history
Radiation degradation
Degradation prediction
Recent R&D activities

42. Recent R&D Activity on Space Solar Cells
Realize a high specific power solar paddle
Require
1. A high specific power solar cell in a sheet (1.0W/g) An ultra-lightweight panel structure

43. Recent R&D Activity on Space Solar Cells
InGaAs bottom-cell
InGaAs bottom-cell
InGaP top-cell
GaAs bottom-cell
Ge substarte
InGaP top-cell
GaAs middle-cell
InGaAs bottom-cell
Drastic weight reduction and flexibilization of multi-junction high-efficiency space solar cells by removal of “heavy” Ge substrate

44. Recent R&D Activity on Space Solar Cells
Current 3J cell (150μm thick, 2.2 grams)
Developed 3J cell (30μm thick, 0.25 grams)

45. Recent R&D Activity on Space Solar Panels
Supporting layer
Thin 3J cell
Front contact
Back contact
Thin-film cell
Laminating Film
Adhesive
Interconnector
N-side tab
P-side tab
Cell-array sheet
Lightweight panel
Solar cell sheet
Panel frame

46. Recent R&D Activity on Space Solar Cells
27.4 cm2, 330 mg, ~30μm
AM0,
InGaP/GaAs/InGaAs Triple-junction Solar Cell
Specific Power: 3.6 W/g

47. Recent R&D Activity on Space Solar Sheets Cross section structure
Thin coverglass
Adhesive
IMM-3J Cell
Backsheet material
Cross section structure
Thickness: ~ 0.3 mm
Weight: ~30 g
Specific Power: 0.58 W/g

48. Recent R&D Activity on Space Solar Panels
Demonstration panel has been mounted on a vacant panel slot on HTV-6
Space Demonstration Test

49. Recent R&D Activity on Space Solar Panels Lightweight Solar Paddle
Stowed
Deployed
Lightweight Solar Paddle

50. Recent R&D Activity on Space Solar Panels
Features：
Lightweight,
Compact,
but Tough
Curved, thin frame
Lightweight and thin frame + SSS　
SSSs applied with Velcro fasteners

51. Recent R&D Activity on Space Solar Panels
Innovative Technology Demonstration Sat-1