Mitsuru ImaizumiHTV-5

Spacecraft Power System, Kyusyu Inst. Tech. Dec. 11, 2015

2

1. Operation principle and fundamentals

2. Radiation damage and effects

3. Radiation degradation characteristics4-1. Single-junction solar cell4-2. Multi-junction solar cell

Contents

3

1. Operation principle and fundamentals

2. Radiation damage and effects

3. Radiation degradation characteristics4-1. Single-junction solar cell4-2. Multi-junction solar cell

Contents

High efficiency Si solar cell

Cell size:2×2 cm2

InGaP/GaAs/Ge triple-junction solar cell

Size: 40mm×60mm Size: 37mm×76mm

Bypass diode Inter-connector

Space Solar Cells

Buried bypass diodes

4

Operation Principle

Eg

empty

filled with electrons

Electrons

Holes

Intrinsic N-type P-type

Energy band in semiconductor

5

Operation Principle

n-typeEmitterLayer

DepletionLayer

p-typeBase Layer

BSFLayer

Ev

Ec

Eg

Eph (>Eg)

Hole

ElectronDiffusion

Drift

Excitation(Generation)

Absorptionv

WindowLayer

6

Current in Solar Cell

VIph Id

I

+_

7

Current-Voltage (I-V) characteristics

-60

-40

-20

0

20

40

60

-1 -0.5 0 0.5 1Voltage (V)

CurrentDensity

(mA/cm 2)

dark

Output Characteristics

(a) Under dark (b) Under light

-60

-40

-20

0

20

40

60

-1 -0.5 0 0.5 1Voltage (V)

CurrentDensity

(mA/cm 2)

light

Photo- generation current

8

-60

-40

-20

0

20

40

60

-1 -0.5 0 0.5 1Voltage (V)

CurrentDensity

(mA/cm2)

darklightpower

Voc

Isc Pmax

phB

ITk

qVII

1exp0

0

lnII

qTk

V scBoc

phsc II

Output Characteristics

9

I-V Curve (Solar Cell Output)

0

10

20

30

40

50

60

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7Voltage (V)

Cur

rent

Den

sity

(mA

/cm

2 ) Isc

Voc

Pmax (Im,Vm)

FF = ImVm / IscVoc

h = Pmax / Po

Output Performance Parameters

10

0

5

10

15

20

0 0.5 1 1.5 2 2.5 3Voltage (V)

Cur

rent

Den

sity

(mA

/cm

2 )

Jsc=16.9mA/cm2

Voc=2.652VFF=0.816h=27.0%

I-V Characteristics of a 3J solar cell

Output Performance

11

Spectral Response

Quantum Efficiency of a high efficiency Si solar cell

0

20

40

60

80

100

300 400 500 600 700 800 900 1000 1100 1200

Wavelength (nm)

Qua

ntum

Eff

icie

ncy

(%)

%100)()()(

in

photon

outelectron

NNQE

12

Equivalent Circuit of Solar Cell

V

Rs

RshIph

VdId

Ish

= 0

= ∞n = 1

1exp0 Tk

qVIIIB

phsh

s

B

sdph R

IRVTnkIRVqIII

1exp0

I

13

0

0.05

0.1

0.15

0.2

0.25

250 500 750 1000 1250 1500 1750 2000Wavelength (nm)

Spec

trum

Irra

dian

ce (m

W/n

m/c

m2 ) AM0

0

1

2

3

4

5

6

7

0.5 1 1.5 2 2.5 3 3.5 4Photon Energy: Eph (eV)

Num

ber o

f Pho

tons

(×10

14/e

V/c

m2 /s

)

AM0

Ideal Current Output of Solar Cell

14

0

1

2

3

4

5

6

7

0.5 1 1.5 2 2.5 3 3.5 4Photon Energy: Eph (eV)

Num

ber o

f Pho

tons

(×10

14/e

V/c

m2 /s

)

AM0

0

1

2

3

4

5

6

7

8

9

0 0.5 1 1.5 2 2.5 3 3.5 4Photon Energy: Eph (eV)

Num

ber o

f Pho

tons

in E

>E p

h (×1

0 17

/cm

2 /s)

AM0

Ideal Current Output of Solar Cell

15

0

1

2

3

4

5

6

7

8

9

0 0.5 1 1.5 2 2.5 3 3.5 4Photon Energy: Eph (eV)

Num

ber o

f Pho

tons

in E

>E p

h (×1

0 17

/cm

2 /s)

AM0

0

20

40

60

80

100

120

0 0.5 1 1.5 2 2.5 3 3.5 4Energy gap: Eg (eV)

Idea

l Sho

rt-C

ircui

t Cur

rent

(mA

/cm

2 )

AM0

Ideal Current Output of Solar Cell

16

0

20

40

60

80

100

0.5 1 1.5 2 2.5 3 3.5 4Energy gap: Eg (eV)

Idea

l Sho

rt-C

ircu

it C

urre

nt (m

A/c

m2 )AM0

Ideal Current/Voltage Output of Solar Cell

17

18

Sun Light Sun Light

0

1

2

3

4

5

6

7

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0Photon Energy (eV)

Inte

grat

ed P

hoto

n N

umbe

r(×

1017

/cm

2 /s)

AM0

0

1

2

3

4

5

6

7

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0Photon Energy (eV)

Inte

grat

ed P

hoto

n N

umbe

r(×

1017

/cm

2 /s)

AM0

Ideal Current/Voltage Output of Solar Cell

Output current estimation

×0

20

40

60

80

100

300 600 900 1200 1500

Wavelength (nm)Q

uant

um E

ffic

ienc

y (%

)

0

1

2

3

4

5

6

250 500 750 1000 1250 1500 1750 2000

Wavelength (nm)

Num

ber

of P

hoto

ns (×

1014

/nm

/cm

2 /s)

AM0

dNQEI )()(q phph

Spectral Response

19

20

1. Operation principle and fundamentals

2. Radiation damage and effects

3. Radiation degradation characteristics4-1. Single-junction solar cell4-2. Multi-junction solar cell

Contents

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)

N-region

ElectronHole

Light

Defect

High-energyparticles

P-region Loss

Radiation Damage in Solar Cell

21

Operation Principle

n-typeEmitterLayer

DepletionLayer

p-typeBase Layer

BSFLayer

Ev

Ec

Eg

Eph (>Eg)

Hole

ElectronDiffusion

Drift

Excitation(Generation)

Absorptionv

WindowLayer

22

Radiation Degradation

n-typeEmitterLayer

DepletionLayer

p-typeBase Layer

BSFLayer

Ec

Ev

Eg

Hole

ElectronDiffusion

Recombination

DefectState

WindowLayer

23Minority-carrier recombination

Before irradiation

Majority-carrier reduction24

After irradiation

Holes

Electrons

Holes

DefectState

Radiation Degradation

Equivalent Circuit of Solar Cell

V

Rs

RshIph

n

sh

s

B

sdph R

IRVTnkIRVqIII

1exp0

I

25

少数キャリア寿命低下の影響

I

V

R s

R shI ph

= 0

= ∞

0

lnII

qTk

V scBoc

0

10

20

30

40

50

60

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7Voltage (V)

Cur

rent

Den

sity

(mA

/cm

2 )

7 μs

5 μs

3 μs

1 μs0.1 μs

0.01 μs

放射線による性能劣化

26

I

V

R s

R shI ph

= 0

0

10

20

30

40

50

60

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7Voltage (V)

Cur

rent

Den

sity

(mA

/cm

2 )

∞ Ω

100 Ω

20 Ω

10 Ω

5 Ω

2 Ω

shBph R

VTk

qVIII

1exp0

Effect of shunt resistance decrease

27

0

10

20

30

40

50

60

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7Voltage (V)

Cur

rent

Den

sity

(mA

/cm

2 )

0 Ω

0.2 Ω

0.5 Ω

1 Ω

2 Ω

5 Ω

I

V

R s

R shI ph = ∞

1exp0 Tk

IRqVIIIB

sph

Effect of series resistance increase

28

Decrease in output power

Cell size:2×2 cm2

Output Performance Degradation

Degradation trend (Pmax)

0

10

20

30

40

50

60

70

80

10MeV Proton Fluence (cm-2)M

axim

um P

ower

(mW

) BOL

EOL

1015Initial 1010 1011 1012 1013 10140

50

100

150

200

0 100 200 300 400 500 600Voltage (mV)

Cur

rent

(mA

)

照射量 大

Irradiation

29

Degradation trend of high-efficiency Si solar cell

Degradation Trend

0

100

200

300

400

500

600

10MeV-Proton Fluence (cm-2)

Val

ue

Isc(mA)Voc(mV)Pmax(mW)

1015Initial 1010 1011 1012 1013 1014

Size: 2cm×2cm

0

0.2

0.4

0.6

0.8

1

10MeV-Proton Fluence (cm-2)

Rem

aini

ng F

acto

r

IscVocPmaxFF

1015Initial 1010 1011 1012 1013 1014

(a) Absolute values (b) Remaining factors

30

Introduction of minority carrier recombination centers Change in minority carrier diffusion length (L)

Introduction of majority carrier traps Change in majority carrier concentration (p)

Decrease in carrier concentration (p) Increase in resistivity (r) and depletion region width (W)

LKLLL

2

022

111

p p p RC 0

pqp r 1

qpV

W bi02

Radiation Damage in Solar Cell

31

32

1. Operation principle and fundamentals

2. Radiation damage and effects

3. Radiation degradation characteristics4-1. Single-junction solar cell4-2. Multi-junction solar cell

Contents

B doped p-Si (100) base10 Wcm (2×1015cm-3)

p+-Si back surface field

Ti/Pd/Ag contactAl back surface reflector

Ti/Pd/Ag contactsAR coating (TiO2/Al2O3)

P doped n+-Si emitter

x j = 0.15 m

50/100 m

Degradation of Single-junction Solar Cell

Structure of sample solar cell

33

Degradation trend of high-efficiency Si solar cell (a) 10MeV protons (b) 1MeV electrons

0

0.2

0.4

0.6

0.8

1

Rem

aini

ng F

acto

r

Fluence (cm-2 )1011 1015101410131012

0

0.2

0.4

0.6

0.8

1

Rem

aini

ng F

acto

rFluence (cm-2 )

101710151014 1016 1018

Degradation of Single-junction Solar Cell

34

Low fluence region:Gradual decrease

↓

Transition region:Anomalous increase

in Isc

↓

High fluence region:Drastic decrease/

Sudden death

0

0.2

0.4

0.6

0.8

1

10MeV Proton Fluence (cm-2 )

Rem

aini

ng F

acto

r

IscVocPmax

1011 1015101410131012

Degradation of Single-junction Solar Cell

35

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.

I I I q R Ink TSC phS SC

B

0 1exp NDPph IIII

pNnP LILI ,

WID exp1

rSR

Anomalous Degradation Analysis

36

0

0.2

0.4

0.6

0.8

1R

emai

ning

Fac

tor o

f Is

c

10-MeV Proton Fluence (cm-2 )

Model with Lchange(Conventional

model)

Model with L, Rb, and W change (Proposed model)

Model with L and Rb change

KL = 2× 10-7

RC = 50 cm-1

1011 1015101410131012

Experimental Results

Anomalous Degradation Analysis

37

0

0.2

0.4

0.6

0.8

1R

emai

ning

Fac

tor o

f Vo

c

10-MeV Proton Fluence (cm-2 )

Vnk Tq

IIOC

B SC

ln

0

1

Conventional model

Proposed model

1011 1015101410131012

Experimental Results

KL = 2×10-7

RC = 50 cm-1

Anomalous Degradation Analysis

38

0

0.2

0.4

0.6

0.8

1R

emai

ning

Fac

tor o

f Pm

ax

10-MeV Proton Fluence (cm-2 )

1011 1015101410131012

P FF I VSC OCmax

Proposed model

Conventional model

Experimental Results

KL = 2×10-7

RC = 50 cm-1

Anomalous Degradation Analysis

39

40

1. Operation principle and fundamentals

2. Radiation damage and effects

3. Radiation degradation characteristics4-1. Single-junction solar cell4-2. Multi-junction solar cell

Contents

InGaP top cell

GaAs middle cell

Ge bottom cell(substrate)

~150mEg=0.7eV

~4mEg=1.4eV

Tunnel junction

N-electrode

P-electrode ARC

~0.5mEg=1.8eV

Structure of Space Solar Cell

InGaP/GaAs/Ge triple-junction solar cell

41

Structure of 3J solar cells

Ge sub.

GaAs cellInGaP cell

3MeV Proton

TRIM simulation of 3MeV proton irradiation onto 3J solar cell

InGaP top cell

GaAs middle cell

Ge bottom cell(substrate)

Substrate140m

Epi layers~10m

P-electrode

N-electrode ARC

Degradation of Multi-junction Solar Cell

42

0

0.2

0.4

0.6

0.8

1

0.01 0.1 1 10Proton Energy (MeV)

Rem

aini

ng F

acto

r

VocIscPmax

=1×1012 cm-2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1MeV Electron Fluence (cm-2)

Rem

aini

ng F

acto

r

VocIscPmax

1015 1016 1017 10181013 1014

Degradation of Multi-junction Solar Cell

Degradation trend curves Energy dependence of remaining factors

43

0.2

0.4

0.6

0.8

1

10MeV Proton Fluence (cm-2)

Rem

aini

ng F

acto

r of I

sc

InGaP TopInGaAs MiddleGe Bottom

1015Initial 1010 1011 1012 1013 10140.2

0.4

0.6

0.8

1

10MeV Proton Fluence (cm-2)R

emai

ning

Fac

tor o

f Voc

InGaP TopInGaAs MiddleGe Bottom

1015Initial 1010 1011 1012 1013 1014

Degradation of Sub-cells in 3J Solar Cell

Isc degradation Voc degradation

44

0

20

40

60

80

100

200 600 1000 1400 1800Wavelength (nm)

EQ

E (%

)

Top cell Middle cell

Bottom cell

Radiation-hardening of 3J Solar Cells

Spectral response of 3J cell Estimation of Isc of sub-cells in irradiated 3J solar cells

45