CRYSTALLINE SILICON SOLAR CELLS – TOWARDS THE LIMIT … · TOWARDS THE LIMIT AND BEYOND What is...

© Fraunhofer ISE

CRYSTALLINE SILICON SOLAR CELLS – TOWARDS THE LIMIT AND BEYOND

Stefan Glunz

Fraunhofer Institute for Solar Energy Systems ISE

Becquerel-Award Ceremony

29th EU PVSEC, Amsterdam

24. September 2014

© Fraunhofer ISE, S. Glunz, September 2014

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CRYSTALLINE SILICON SOLAR CELLS – TOWARDS THE LIMIT AND BEYOND What is the limit?

Shockley-Queisser vs Auger

Towards the limit

Recombination losses

Volume

Surfaces

Contacts

Recent results

Beyond the limit

III/V on silicon

Perovskites on silicon


3



Towards the limit


Volume

Surfaces

Contacts

Recent results

Beyond the limit

III/V on silicon



4

What is the limit? Detailed Balance

Shockley und Queisser, 1961

Detailed balance between sun and solar cell

Assumption: Solar cell emits photons via radiative recombination

Radiative recombination in a direct semiconductor

E

k

W. Shockley & H. Queisser


5

What is the limit? Maximum Efficiency as a Function of Bandgap

Max. Efficiency ~ 33%

High thermalisation for low bandgaps

High transmission for high bandgaps

Silicon and GaAs are close to the optimum

But: Record values of GaAs are closer to the limit.

Is III/V-R&D better than silicon-R&D ?

Thermalisation Transmission

0.5 1.0 1.5 2.0 2.50.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

GeGaSb

mc-Si

c-Si

CIGSInP

GaAs

CdTe

a-Si AlGaAs

Shockley-Queisser Record Efficiencies

EG [eV]

Effic

ienc

y


6

What is the Limit? Other Recombination Channels

Assumption: Ideal solar cell: only radiative recombination (Shockley and Queisser, J. Appl. Phys. 1961)

But silicon is an indirect semiconductor radiative recombination has a low probability

Radiative recombination in an indirect semiconductor

E

k

Phonon


7

What is the limit? Auger-Recombination

In silicon solar cells Auger-recombination is the limiting intrinsic loss mechanism

Auger recombination in an indirect semiconductor

Pierre Auger 1899 - 1993

E

k

BZB


8

What is the limit? Taking Auger Recombination into Account

Shockley, Queisser (1961) = 33% (AM1.5)

Theoretical efficiency limit for silicon (taking actual Auger model 1 into account) = 29.4%2

1Richter, Glunz et al., Phys. Rev. B 86 (2013) 2Richter, Hermle, Glunz, IEEE J. Photovolt. (2013)


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What is the limit? Taking Auger Recombination into Account

Shockley, Queisser (1961) = 33% (AM1.5)

Theoretical efficiency limit for silicon (incl. Auger) = 29.4%1

Best silicon solar cells = 25.6%2

Corresponds to 87% of theoretical efficiency limit

(GaAs = 87% ) 0,5 1,0 1,5 2,0 2,5

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

GeGaSb

mc-Si

c-Si

CIGSInP

GaAs

CdTe

a-Si AlGaAs

Shockley-Queisser Record Efficiencies

EG [eV]

Effic

ienc

y

1Richter, Hermle, Glunz, IEEE J. Photovolt. (2013) 2Masuko et al., IEEE-PVSC (2014)


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Towards the limit


Volume

Surfaces

Contacts

Recent results

Beyond the limit

III/V on silicon



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1940 1950 1960 1970 1980 1990 2000 2010 20200

5

10

15

20

25

30

mono-Si (p-type) mono-Si (n-type) multi-Si (p-type)

Effic

ienc

y [%

]

Towards the Limit Small-area Record Values

Small-area record cells Mono-Si:

25.0% (da) (PERL, UNSW 1999)

Data from M.A. Green, PIP 17, p.183 (2009)

29.4%

ap = aperture area da = designated area


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1940 1950 1960 1970 1980 1990 2000 2010 20200

5

10

15

20

25

30


Effic

ienc

y [%

]



25.0% (da) (PERL, UNSW 1999)

Multi-Si: 20.4% (ap) (LFC, ISE 2004)


29.4%



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1940 1950 1960 1970 1980 1990 2000 2010 20200

5

10

15

20

25

30


Effic

ienc

y [%

]



25.0% (da) (PERL, UNSW 1999)

Multi-Si: 20.4% (ap) (LFC, ISE 2004)

Since 1974 nearly only records on p-type silicon

Main progress: Reduction of recombination losses


29.4%



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Cells with excellent surface passivation

Experimental thickness variation

Towards the Limit Influence of Surface and Bulk Recombination

Diffusion length High (Lb>> 250 µm) Medium (Lb≈ 250 µm) Low (Lb<< 250 µm)

0 50 100 150 200 25018

19

20

21

22

Effic

ienc

y %

]

Thickness [µm]

Glunz, 3rd Workshop on the Future Direction of Photovoltaics, Tokyo (2007)


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Defect engineering during cell process

Very thin wafers (99 µm) to reduce influence of volume recombination

Plasma texture on front side

World record on multicrystalline silicon (20.4%)

Towards the Limit Multicrystalline Silicon

Schultz, Glunz, Willeke, Prog. Photovolt. 12 (2004)


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Towards the Limit Monocrystalline Silicon

Additional bulk recombination in p-type Cz-grown silicon

Light-induced degradation

Metastable defect related to boron and oxygen1

1 Glunz et al., WCPEC/EUPVSEC, Vienna (1998)

0 1000 2000 3000 4000 5000 60000%

20%

40%

60%

80%

100%

Oxygen-free boron-doped FZ-Si Oxygen-doped phosphorus-doped FZ-Si

Oxygen-doped boron-doped FZ-Si Oxygen-contaminated boron-doped Cz-SiR

elat

ive

Life

time

Leve

l [%

]

Time [min]


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July 1998, 2nd World Conference, Vienna

1 Glunz et al., EUPVSEC, Vienna (1998)


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Towards the Limit Monocrystalline Silicon

Additional bulk recombination in p-type Cz-grown silicon

Light-induced degradation

Metastable defect related to boron and oxygen1

Gallium–doped silicon2

n-type silicon

1 Glunz et al., EUPVSEC, Vienna (1998)

2 Glunz et al., Progress Photovoltaics 7 (1999)

0.42 0.28 0.41 0.2 0.8 1.2 1.1 1.25 0.5 16

17

18

19

20

21

22

23

Effi

cien

cy [

%]

Base Resistivity

Ga-doped Cz

B-doped Cz

B-doped FZ


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Towards the Limit Large-area Record Cells

Panasonic/Sanyo 1 Masuko et al., IEEE PVSC (2014)

SunPower 2 Smith et al., IEEE PVSC (2014)

Interdigitated back contact back junction solar cells

Excellent contact passivation (a-Si/c-Si heterojunction, passivated contacts)

Sanyo1 (da=143.7 cm2) 25.6% (Voc = 740 mV)

SunPower2 (ap=121 cm2) 25.0% (Voc = 726 mV)

Edge losses are getting crucial


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1940 1950 1960 1970 1980 1990 2000 2010 20200

5

10

15

20

25

30

mono-Si (p-type) mono-Si (n-type)

Effic

ienc

y [%

]

Towards the Limit Large-area Record Cells

Large-area (Sunpower, Sanyo/Panasonic)

Extremely high lifetimes needed (>> 1 ms)

Usage of n-type silicon to avoid light-induced degradation

29.4%

Large area

Small area


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Towards the limit


Volume

Surfaces

Contacts

Recent results

Beyond the limit

III/V on silicon



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Si (1.12 eV)

Beyond the Limit Magic Antireflection Coatings (AAA-Coating®)

Si (1.12 eV)

Silicon Solar Cells with AAA-Coating®

(amazingly active antireflection coating)

Si (1.12 eV)

GaAs (1.42 eV)

GaInP (1.88 eV)

AAA- Coating®


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Beyond the Limit Silicon Solar Cell

Theoretical limit for Eg,Si: 33% (29.4% incl. Auger)

Word record for silicon solar cells: 25.6%

400 600 800 1000 1200 1400 1600 1800 20000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Transmission loss

Bandgap

Usable power

Thermalization loss

Inte

nsity

[W m

-2nm

-1]

Wavelength [nm]


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Beyond the Limit Multijunction Solar Cells

Succesfully realized with III/V-materials

400 600 800 1000 1200 1400 1600 1800 20000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

AM1.5 1. Cell 2. Cell 3. Cell (Si)

Inte

nsity

[W m

-2nm

-1]

Wavelength [nm]


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Beyond the Limit Multijunction Solar Cells

Succesfully realized with III/V-materials

Tandem cells with Si bottom cell

III/V on Si

Silicon quantum dots

Perovskites

“Silicon Solar Cell 2.0”

400 600 800 1000 1200 1400 1600 1800 20000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

AM1.5 1. Cell 2. Cell 3. Cell (Si)

Inte

nsity

[W m

-2nm

-1]

Wavelength [nm]


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Beyond the Limit Silicon-based Multijunction Cells

Si (1.12 eV)

GaAs (1.42 eV)

GaInP (1.88 eV)

Top cells with high bandgap to utilize blue and visible light

c-Si bottom cells for IR light

Deposition by direct epitaxial growth or wafer bonding


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Beyond the Limit GaInP/GaAs/Si Solar Cells

K. Derendorf et al., IEEE JPV (2013)

S. Essig, PhD Thesis (2014)

400 600 800 1000 12000

20

40

60

80

100

10.1mA/cm²

12.0mA/cm²

10.7mA/cm²

C1217-invtan-4-Bond180-x22y2, Photo currents under AM1.5dA = 0.0547cm²

Wavelength [nm]Ex

tern

al Q

uant

um E

fficie

ncy

[%]

Efficient utilization of spectrum

High efficiency

Wafer bonfing

But: Cell design optimized for concentration and AM1.5d

More to come quite soon

1 2.89 10.1 87.8 25.6 112 3.40 1129 88.3 30.2

C [suns]

Voc

[V]

Jsc

[mA/cm2]

FF [%]

η [%]

GaInP GaAs Si


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Conclusion

25%

Crystalline silicon, the vital dinosaur, hunting record efficiencies. (pretty active for a first generation)


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Conclusion

Crystalline silicon, the vital dinosaur, hunting for record efficiencies (pretty active for a first generation)

Coming soon: Crystalline silicon solar cells 2.0

Let‘s show Pierre A. what we can do !


30

Conclusion

Crystalline silicon, the vital dinosaur, hunting for record efficiencies (pretty active for a first generation)

Coming soon: Crystalline silicon solar cells 2.0

Let‘s show Pierre A. what we can do !

CRYSTALLINE SILICON SOLAR CELLS – TOWARDS THE LIMIT … · TOWARDS THE LIMIT AND BEYOND What is...

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