METALLIZATION OF PASSIVATING AND CARRIER SELECTIVE ...€¦ · Main stream technology Intrinsic efficiency limitation by J 0,met >> J 0,pass Passivating contacts

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METALLIZATION OF PASSIVATING AND CARRIER SELECTIVE CONTACTS: STATUS AND PERSPECTIVES AT FRAUNHOFER ISE

M. Bivour, J. Bartsch, F. Clement, G. Cimiotti, D. Erath, F. Feldmann, T. Fellmeth, M. Glatthaar, M. Hermle, M. Jahn, S. Kluska, R. Keding, A. Lorenz, I. Lacmago-Lontchi, S. Mack, A. Moldovan, J. Nekarda, M. Pospischil, A. Rodofili, J. Rentsch, B. Steinhauser, J. Schube, L. Tutsch, W. Wolke and R. Preu, S. W. Glunz

Fraunhofer Institute for Solar Energy Systems ISE

7th Metallization Workshop Konstanz, 24th October 2017

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Passivating Contacts Overcoming Recombination at Metallized Regions

Homojunction + fire-through contacts

Main stream technology

Intrinsic efficiency limitation by J0,met >> J0,pass

Passivating contacts

J0,met = J0,pass

Current challenge:

Establishing industrial cell process including metallization and module integration

Graph adapted from M. Bivour, PhD thesis, University of Freiburg (2015)

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Passivating Contacts Amorphous Silicon Heterojunction (SHJ)

Champion efficiencies for c-Si solar cells1,2

Back-end process temp. only ~220°C

Not compatible with main stream c-Si technology

Adapted metal electrodes and cells interconnection

Lower line conductivity

a-Si(i)

a-Si(n)

a-Si(p)

TCO

TCO

Si-absorber

1K. Yoshikawa et al., Nature Energy, 2:17032 (2017) 2D. Adachi et al., APL, 107, 233506 (2015)

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wf,∅ = 34 μm / hf,max∅ = 20 μm

Screen Printing* Low Temperature Ag Paste

Various low-T Ag pastes and drying/curing conditions evaluated

Baseline process: single print

Aspect ratio up to 0.3

Advanced process: double print

Aspect ratio up to 0.6

Finger resistivity ρfinger ~ 6 µΩcm

Contact resistivity ρc < 5 mΩcm2

Double print: 30 µm screen

wf,∅ = 56 μm / hf,max∅ = 13 μm

Single print: 50 µm screen

*D. Erath et al., Energy Procedia, 124, 869-874 (2017)

SHJ

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Screen Printing* Cell Results

Industrial solar cell precursors

5-busbar layout

Bifacial

Efficiency up to 21.9%

Metallization Area VOC JSC FF η [cm²] [mV] [mA/cm²] [%] [%]

Single print (50 µm) 239 727 37.6 80.1 21.9 best cell, 5-busbar, monofacial measurement, black chuck

*D. Erath et al., Energy Procedia, 124, 869-874 (2017)

wf,∅ = 56 μm / hf,max∅ = 13 μm

Single print: 50 µm screen

SHJ

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Ink Jet Printing* Towards Lower Ag Consumption

Substrate heating for in-situ drying and ink wetting

Width down to 32 μm for nano-silver-ink

To be tested on cell level

Multi-busbar layout

Seed layer for selective plating using self passivating metal as plating mask1

*D. Erath et al., Energy Procedia, 124, 869-874 (2017) 1M. Glatthaar et al., IEEE J-PV, 99, 1-5 (2017)

SHJ

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7 *A. Rodofili et al., Sol. RRL 1 (2017)

TCO a-Si(i/n)

c-Si(n)

dielectric

plated Ag plated Cu

Laser Transfer and Firing of Seed Layer (LTF) + Plating* Overcoming the Need for Plating Resist SHJ

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TCO a-Si(i/n)

c-Si(n)

Laser Transfer and Firing of Seed Layer (LTF) + Plating* Overcoming the Need for Plating Resist

*A. Rodofili et al., Sol. RRL 1 (2017)

SHJ

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TCO a-Si(i/n)

c-Si(n)

dielectric

Laser Transfer and Firing of Seed Layer (LTF) + Plating* Overcoming the Need for Plating Resist


SHJ

Dielectric layer on TCO as plating mask

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TCO a-Si(i/n)

c-Si(n)

dielectric

laser transfer

Foil NiV

*A. Rodofili et al., Sol. RRL 1 (2017) 1J. Bohandy et al., Journal of Applied Physics 60, 1538 (1986).



Laser induced forward transfer1 of seed layer

Transparent plastic foil with NiV layer

No laser damage

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TCO a-Si(i/n)

c-Si(n)

dielectric

laser firing

*A. Rodofili et al., Sol. RRL 1 (2017) 1J. Bohandy et al., Journal of Applied Physics 60, 1538 (1986).





No laser damage

Laser firing of seed layer through dielectric

Formation of contact to TCO

No laser damage

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TCO a-Si(i/n)

c-Si(n)

dielectric

plated Ag plated Cu




No laser damage

Laser firing of seed layer through dielectric

Formation of contact to TCO

No laser damage

Pulse plating to reduce parasitic plating2

*A. Rodofili et al., Sol. RRL 1 (2017) 1J. Bohandy et al., Journal of Applied Physics 60, 1538 (1986) 2M. Glatthaar et al., IEEE J-PV, 99, 1-5 (2017)


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Industrial precursors

5-busbar layout

Monofacial

Encouraging result for first cell batch

No laser damage

Optics and electrics improved compared to screen printing reference

30 µm

Metallization Area VOC JSC FF η [cm²] [mV] [mA/cm²] [%] [%]

Screen printing 239 727 37.8 79.1 21.7 LTF + Cu plating 239 728 38.0 80.1 22.2

best cells, 5 busbar, monofacial, industrial precursors



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Passivating Contacts* Poly-Si and TOPCon

Back-end process temp. > 220°C

Potentially, more compatible with main stream technology

Currently, evaluation of suitable back-end processes

thin SiOx

doped c-Si emitter

doped Si-film

Passivation / ARC

Homojunction front

Poly-Si or TOPCon rear

? ? ? ? ? ? ? ? ? ? ? ? ? ? ?

Si-absorber

*Y. Kwark PhD thesis, Stanford Univ. (1985) *F. Feldmann et al., SOLMAT, 120, 270-274 (2014) *U. Römer et al., SOLMAT, 131, 85-91 (2014)

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40nm n-type TOPCon 800°C Firing of Commercial Ag Screen Printing FT Pastes

SiNx capping

Poor contact

c-Si(n) thin SiOx

n-type Si-film

80nm SiNx

P1 P2 P3 P4

1

10

100

1000

80nm SiNx

ρ c (mΩ

cm2 )

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SiNx capping

Poor contact

c-Si(n) thin SiOx

n-type Si-film

80nm SiNx

P1 P2 P3 P4

1

10

100

1000

80nm SiNx

ρ c (mΩ

cm2 )

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SiNx capping

Poor contact

Likely, contact to lowly doped absorber

c-Si(n) thin SiOx

n-type Si-film

80nm SiNx

P1 P2 P3 P4

1

10

100

1000

80nm SiNx

ρ c (mΩ

cm2 )

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SiNx capping

Poor contact

Likely, contact to lowly doped absorber

ITO / SiNx capping

Very good contact

Likely, contact to highly doped ITO or Si-film

c-Si(n) thin SiOx

n-type Si-film

20nm SiNx

150nm ITO


P1 P2 P3 P4

1

10

100

1000

80nm SiNx

150nm ITO / 20nm SiNx

ρ c (mΩ

cm2 )

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300nm p-type Poly-Si* Firing of Commercial Ag Screen Printing FT Pastes

Low J0,pass

c-Si(p) thin SiOx

p-type Si-film

*S. Mack et al., EUPVSEC, (2017)

80nm SiNx

before firing

780°C810°C

840°C870°C

900°C0

2

4

6

8

10

12

14

16SDE surface, SiNx

J0,

pass

(fA

/cm

2 )

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Low J0,pass

J0,met increases with Tfiring

J0,met >> J0,pass

780 810 840 870 90010

100

1000 Ag 1 Ag 2 Ag 3

J 0,m

et (f

A/c

m2 )

Firing set temperature (°C)

c-Si(p) thin SiOx

p-type Si-film


80nm SiNx

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Low J0,pass


J0,met >> J0,pass

Local penetration / damage of poly-Si*,1

c-Si(p) thin SiOx

p-type Si-film

900°C

80nm SiNx

*S. Mack et al., EUPVSEC, (2017) 1H.E. Çiftpinar et al., Energy Procedia, 124, 851-861 (2017)

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Low J0,pass


J0,met >> J0,pass

Local penetration / damage of poly-Si*,1

Low ρc for Ag2

c-Si(p) thin SiOx

p-type Si-film

80nm SiNx

780 810 840 870 9001

10

100

1000

Ag1 Ag2 Ag3

ρ c (mΩ

cm2 )

Firing set temperature (°C)

SDE surface, SiNx

*S. Mack et al., EUPVSEC, (2017) 1H.E. Çiftpinar et al., Energy Procedia, 124, 851-861 (2017)

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300nm p-type Poly-Si Firing of Commercial Ag Screen Printing FT Pastes

840°C

J0,pass ≈ 5fA/cm2

J0,met ≈ 250fA/cm2

ρc = 2mΩcm2


80nm SiNx

c-Si(p) thin SiOx

p-type Si-film

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Non-Firing Approach: Evaporated Ag High Efficiency Front Side Required

High efficiency homojunction front essential to benefit from passivating contact at rear

TOPCon + evaporated Ag

J0,met = J0,pass

25.8%1 lab-type cells

Metallization Area VOC JSC FF η

Front / Rear [cm²] [mV] [mA/cm²] [%] [%] Photolithography / evaporated Ag 4 (da) 724 42.9 83.1 25.81

Certified by Fraunhofer ISE CalLab, da: designated area

1A. Richter et al., EUPVSEC, (2017)

p++

busbar DARC: SiNx + MgF2

Al2O3

p+

evaporated Ag

thin SiOx

n-type Si-film

c-Si(n)

selective boron emitter

finger

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Non-Firing Approach: Evaporated Ag First Cell Batch Practicale Size

Homogeneous boron emitter

LCO + Cu-plating front side

TOPCon + evaporated Ag

22.9%1

Metallization Area VOC JSC FF η Front / Rear [cm²] [mV] [mA/cm²] [%] [%]

LCO + Cu-plating / evaporated Ag 100 (ap) 694 40.8 81.0 22.91

In-house measurement, ap: aperture area

SiNx/AlOx ARC

1F. Feldmann et al., EUPVSEC, (2017)

evaporated Ag

c-Si(n)

homogeneous boron emitter

thin SiOx

n-type Si-film

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metal

TCO

Non-Firing Approach Current Work

TCO / metal stacks

Similar to SHJ but >> 200°C

evaporated Ag

c-Si(n)

homogeneous boron emitter

metal

TCO

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Summary

Amorphous Silicon Heterojunction (Tback-end < 220°C)

Baseline screen printing process (η = 21.9%)

Ink jet printing of nano-silver ink promising for multi-busbar / plating

Novel laser transfer of seed layer + Cu plating (η = 22.2%)

TOPCon and poly-Si (Tback-end > 220°C)

So far, J0,met >> J0,pass for firing-through metallization

Only commercial Ag pastes investigated

Hence, lots of room for improvement for paste optimization

Non-firing approach under evaluation

LCO + Cu-plating for high performance diffused front side

TCO + metal optimized for > 220°C

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Acknowledgments

Part of this work was funded by German Federal Ministry for Economic Affairs and Energy under contract number 03225877D (PEPPER) 0324086A (HIPPO) 0325574 (Folmet) 0325825B (HERA) 0324125 (PV BAT 400) and by the EU’s HORIZON 2020 programme for research, technological development and demonstration under grant agreement no. 727529 (PROJECT DISC)

Thank You Very Much for Your Attention!

The authors would like to thank all colleagues at Fraunhofer ISE

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Approach 2: Selective plating using conductive mask

Al ITO

a-Si(i/n)

c-Si(n)

a-Si(i/p) ITO

Al

Precursor:

M. Glatthaar et al., IEEE J-PV, 99, 1-5 (2017)

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Inkjet

particle-free Ag-ink

Step 1: seed layer print on both sides



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plated Ag plated Cu

Step 2: simultaneous plating on both sides



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plated Ag plated Cu

Step 3: etching of Al layers



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TOPCon TCO Sputterdamage

> 200°C needed to cure damage

Si-absorber thin SiOx

doped Si-film TCO

before ITOafter ITO

200°C 300°C 350°C

660670680690700710720730740

iVoc

(mV

)

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TOPCon TCO Sputterdamage

> 200°C needed to cure damage

> 200°C poor mobility

Trade-off passivation and TCO

Si-absorber thin SiOx

doped Si-film TCO

100 200 300 400 50015

20

25

30

35

40

45

Mob

ility

(cm

²/Vs)

Annealing temperature (°C)

5.0x1019

1.0x1020

1.5x1020

2.0x1020

2.5x1020

3.0x1020

Car

rier d

ensi

ty (c

m-3)

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METALLIZATION OF PASSIVATING AND CARRIER SELECTIVE ...€¦ · Main stream technology Intrinsic efficiency limitation by J 0,met >> J 0,pass Passivating contacts