1. Mitsuru Imaizumi Space Solar Cells -- II -- SLATS
Spacecraft Power System, Kyusyu Inst. Tech Oct. 26, 2018
Space Solar Cells -- II --
SLATS
Mitsuru Imaizumi

2. Contents Operation principle and fundamentals
Radiation damage and effects
Radiation degradation characteristics 4-1. Single-junction solar cell 4-2. Multi-junction solar cell

3. Contents Operation principle and fundamentals
Radiation damage and effects
Radiation degradation characteristics 4-1. Single-junction solar cell 4-2. Multi-junction solar cell

4. 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

5. Energy band in semiconductor
Operation Principle
Intrinsic
N-type
P-type
Energy band in semiconductor

6. Operation Principle

7. Current in Solar Cell V
Iph Id I + _

8. Output Characteristics Current-Voltage (I-V) characteristics
Photo- generation current
(a) Under dark
(b) Under light
Current-Voltage (I-V) characteristics

9. Output Characteristics

10. Output Performance Parameters

11. I-V Characteristics of a 3J solar cell
Output Performance
I-V Characteristics of a 3J solar cell

12. Quantum Efficiency of a high efficiency Si solar cell
Spectral Response
Quantum Efficiency of a high efficiency Si solar cell

13. Equivalent Circuit of Solar CellId Vd Rs
= 0
Iph
Rsh
= ∞ V n
= 1
Ish

14. Ideal Current Output of Solar Cell

15. Ideal Current Output of Solar Cell

16. Ideal Current Output of Solar Cell

17. Ideal Current/Voltage Output of Solar Cell

18. Ideal Current/Voltage Output of Solar Cell
Sun Light
Sun Light

19. Spectral Response
Output current estimation ×

20. Contents Operation principle and fundamentals
Radiation damage and effects
Radiation degradation characteristics 4-1. Single-junction solar cell 4-2. Multi-junction solar cell

21. Radiation Damage in Solar Cell
N-region
Electron
Hole
Light
Defect
High-energy particles
P-region
Loss
Incident of high-energy particles (electrons/protons) ↓
Elastic/non-elastic collision with atoms
Formation of vacancy-interstitial (Flenkel) pairs
(Some defect reactions)
Generation of minority-carrier recombination center(s) and majority-carrier trap(s)

22. Operation Principle

23. Radiation Degradation Minority-carrier recombination

24. Radiation Degradation Majority-carrier reduction
Before irradiation
After irradiation
Majority-carrier reduction

25. Radiation Damage in Solar Cell
Introduction of minority carrier recombination centers
Change in minority carrier diffusion length (L)
Introduction of majority carrier traps
Change in majority carrier concentration (p)

26. Equivalent Circuit of Solar CellRs
Iph
Rsh V n

27. Effect of generation current decrease

28. Effect of shunt resistance decrease

29. Effect of series resistance increase

30. Output Performance Degradation
Cell size: 2×2 cm2
Irradiation
Decrease in output power
Degradation trend (Pmax)

31. Degradation trend of high-efficiency Si solar cell
(a) Absolute values
(b) Remaining factors
Degradation trend of high-efficiency Si solar cell

32. Contents Operation principle and fundamentals
Radiation damage and effects
Radiation degradation characteristics 4-1. Single-junction solar cell 4-2. Multi-junction solar cell

33. Degradation of Single-junction Solar Cell
B doped p-Si (100) base
10 Wcm (2×1015cm-3)
p+-Si back surface field
Ti/Pd/Ag contact
Al back surface reflector
Ti/Pd/Ag contacts
AR coating (TiO2/Al2O3)
P doped n+-Si emitter
x j = 0.15 mm
50/100 mm
Structure of sample solar cell

34. Degradation of Single-junction Solar Cell
(a) 10MeV protons
(b) 1MeV electrons
Degradation trend of high-efficiency Si solar cell

35. Degradation of Single-junction Solar Cell
Low fluence region: Gradual decrease ↓
Transition region: Anomalous increase in Isc
High fluence region: Drastic decrease/ Sudden death

36. Anomalous Degradation Analysis
Short circuit current (Isc) is expressed by
First stage: Reduction of L leads to a decrease in Isc.
Second stage: Reduction of p leads to an increase in W and consequently an increase in Isc.
Third stage: Reduction of p leads to an increase in resistivity and consequently abrupt decrease in Isc.

37. Anomalous Degradation Analysis

38. Anomalous Degradation Analysis
Experimental Results
KL = 2×10-7
RC = 50 cm-1
Anomalous Degradation Analysis

39. Anomalous Degradation Analysis
KL = 2×10-7
RC = 50 cm-1

40. Contents Operation principle and fundamentals
Radiation damage and effects
Radiation degradation characteristics 4-1. Single-junction solar cell 4-2. Multi-junction solar cell

41. Structure of Space Solar Cell InGaP/GaAs/Ge triple-junction solar cell

42. Degradation of Multi-junction Solar Cell Structure of 3J solar cells
InGaP top cell
GaAs middle cell
Ge bottom cell
(substrate)
Substrate
140mm
Epi layers
~10mm
P-electrode
N-electrode
ARC
Structure of 3J solar cells
TRIM simulation of 3MeV proton irradiation onto 3J solar cell

43. Degradation of Multi-junction Solar Cell
Degradation trend curves
Energy dependence of remaining factors

44. Degradation of Sub-cells in 3J Solar Cell
The last is comparison of radiation tolerance of the three sub-cells. This is the first for such trial using the same irradiation facility and the same measurement apparatus as far as we know.
Left hand side is degradation of Isc, and right hand side is that of Voc as a function of 10 MeV proton fluence. For both, InGaP top cell exhibits highest radiation tolrance, while GaAs middle cell shows the lowest. Ge bottom cell has interesting features. Isc tolerance is as low as GaAs middle cell, but Voc tolerance is as high as InGaP top cell.
Isc degradation
Voc degradation

45. Degradation of Sub-cells in 3J Solar Cell
InGaP top-cell
GaAs middle-cell
InGaAs bottom-cell
Graded buffer
Epi layers
~20mm
The last is comparison of radiation tolerance of the three sub-cells. This is the first for such trial using the same irradiation facility and the same measurement apparatus as far as we know.
Left hand side is degradation of Isc, and right hand side is that of Voc as a function of 10 MeV proton fluence. For both, InGaP top cell exhibits highest radiation tolrance, while GaAs middle cell shows the lowest. Ge bottom cell has interesting features. Isc tolerance is as low as GaAs middle cell, but Voc tolerance is as high as InGaP top cell.
Thin Film IMM-3J cell

46. Degradation of Sub-cells in 3J Solar Cell
The last is comparison of radiation tolerance of the three sub-cells. This is the first for such trial using the same irradiation facility and the same measurement apparatus as far as we know.
Left hand side is degradation of Isc, and right hand side is that of Voc as a function of 10 MeV proton fluence. For both, InGaP top cell exhibits highest radiation tolrance, while GaAs middle cell shows the lowest. Ge bottom cell has interesting features. Isc tolerance is as low as GaAs middle cell, but Voc tolerance is as high as InGaP top cell.
Electrons
Protons
Isc degradation

47. Degradation of Sub-cells in 3J Solar Cell
The last is comparison of radiation tolerance of the three sub-cells. This is the first for such trial using the same irradiation facility and the same measurement apparatus as far as we know.
Left hand side is degradation of Isc, and right hand side is that of Voc as a function of 10 MeV proton fluence. For both, InGaP top cell exhibits highest radiation tolrance, while GaAs middle cell shows the lowest. Ge bottom cell has interesting features. Isc tolerance is as low as GaAs middle cell, but Voc tolerance is as high as InGaP top cell.
Electrons
Protons
Voc degradation

48. Degradation of Sub-cells in 3J Solar Cell
The last is comparison of radiation tolerance of the three sub-cells. This is the first for such trial using the same irradiation facility and the same measurement apparatus as far as we know.
Left hand side is degradation of Isc, and right hand side is that of Voc as a function of 10 MeV proton fluence. For both, InGaP top cell exhibits highest radiation tolrance, while GaAs middle cell shows the lowest. Ge bottom cell has interesting features. Isc tolerance is as low as GaAs middle cell, but Voc tolerance is as high as InGaP top cell.
Electrons
Protons
Pmax degradation