© Fraunhofer

transparent front side contact pastes for high efficiency SHJ-solar cells

S. Körner1, A. Waltinger2, M. Eberstein1

1Fraunhofer IKTS; 2Meyer Burger (Germany) AG

© Fraunhofer 2 / 18

future of crystalline silicon solar cell

ITRPV roadmap 2015 predicts efficiencies for SHJT up to 25 % and market share of 10 % in the year 2025

BSF/PERC n-type mono Si

SHJ n-type mono Si

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conventional pastes for front side metallization

800 °C, someseconds Cool down

Ag

glass

Si 200 nm

© Fraunhofer 4 / 18

SHJ cell concept

ITO

emitter: a-Si (p)

passivation: a-Si (i)

base: c-Si (n)

silver-polymer-composite

maximum process temperature ≤200°C

© Fraunhofer 5 / 18

SHJ cell concept

ITO

emitter: a-Si (p)

passivation: a-Si (i)

base: c-Si (n)

maximum process temperature ≤200°C

silver-polymer-compositeinduce power losses due to shading

Why not us ing transparent, intrins ic conductive Polymers?

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intrinsic conductive polymers

conjugated double bonds forms conjungated π- electron system

oxidation / reduction by doping by halogenides or alkaline metals

generating charges along polymer backbone

for charge equalization immobilisation of large counter ions; e.g. sulfonic acids

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intrinsic conductive polymers

conductivity provided by hopping of electrons or holes

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intrinsic conductive polymers

conductivity provided by hopping of electrons or holes

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intrinsic conductive polymers – conductivity comparison

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Experimental

IKTS paste

• dissolved or dry

• adding solvents and other reagents

• optimizing curing profile

• screen print test structures and characterization

pastepreparation

commercial paste

printingsolar cells

IKTS paste

screen printing

• 10 wafer per paste

• 74 fingers with 100 µm width

curing solar cells

30 min @ 120 °C

10 min @ 200 °C

curing characterization

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transparent front side paste – development and characterization

80 120 160

100

1000

10000

sheet re

sis

tsance [m

Ohm

/sq]

temperature [°C]

solvent A

solvent B

solvent C

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SHJ Solar cells – conventional and organic front side metallization

silver free silver

36.0

36.5

37.0

37.5

38.0

38.5

39.0

39.5

Jsc [m

A/c

m²]

silver free silver

0.725

0.730

0.735

0.740

Vo

c [V

]

transparent pastes provides

Higher Jsc than silver paste gain of 1.05 mA/cm²

Higher Voc gain of 4 mV

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SHJ Solar cells – conventional and organic front side metallization

silver free silver

36.0

36.5

37.0

37.5

38.0

38.5

39.0

39.5

Jsc [m

A/c

m²]

gain of Jsc due to transparent paste

Cells without pastes Jsc = 39.4 mA/cm²

6.4 % shading of silver paste leads to decrease down to Jsc = 37.2 mA/cm²

Transparent paste reduces shading down to 1.5 %

no paste transparent silver

35

36

37

38

39

40

Jsc [

mA

*cm

²]

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SHJ Solar cells – conventional and organic front side metallization

silver free silver

0.8

1.0

1.2

1.4

1.6

Rse

r [O

hm

*cm

²]

silver free silver

0.70

0.75

0.80

0.85

FF

silver free silver

20.0

20.5

21.0

21.5

22.0

22.5

23.0

eta

[%

]

gain in Jsc and Voc as well as low series resistance leads to high efficiency of transparent paste

fill factor is 4 % lower than silver containing pastes

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transparent front side paste –characterization

organic Ag gen. 1 Ag gen. 2 Ag gen. 3

1

10

100

sheet re

sis

tsance [m

Ohm

/sq]

paste

sheet resistance comparison of transparent and silver containing pastes

Resistance of transparent pastes ~ 10 times higher than silver paste

adding small amount (< 10 wt%) of silver nanowires to increase conductivity and maintain transparency

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conclusion

conductive polymers can be used for SHJ-front-side contact pastes

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conclusion

conductive polymers can be used for SHJ-front-side contact pastes

transparency increases Jsc and therewith efficiency in the range of conventional silver pastes can beobtained allready in this study

no paste transparent silver

35

36

37

38

39

40

Jsc [m

A*c

m²]

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conclusion

conductive polymers can be used for SHJ-front-side contact pastes

Transparency increases Jsc and therewith efficiency in the range of conventional silver pastes can beobtained allready in this study

sheet resistance somewhat to high adding of silver nanowires will decrease resistance and maintain transparency

no paste transparent silver

35

36

37

38

39

40

Jsc [m

A*c

m²]

organic Ag gen. 1 Ag gen. 2 Ag gen. 3

1

10

100

sheet re

sis

tsance [m

Ohm

/sq]

paste

© Fraunhofer

Thanks to the german Federal Ministry of Education and Research (MWT+ #03SF0420)…

…and you for your attention!

Further Informations:

Stefan Körner

+49-351-2553-7817

stefan.koerner@ikts.fraunhofer.de

Fraunhofer Institut Keramische

Technologien und Systeme

Winterbergstraße 28, 01277 Dresden