CONTACT RECOMBINATION AND MICROSTRUCTURE EVALUATION OF ... · the paste chemistry › Reduced...

CONTACT RECOMBINATION AND MICROSTRUCTURE EVALUATION OF SCREEN PRINTED AND FIRING-THROUGH METALLIZATION Konstanz, 24.10.2017, Matthias Hörteis

CONTACT FORMATION

Metallization workshop 2017, Konstanz | Matthias Hoerteis |

Gary C. Cheek et. Al. “Thick film metallization for solar cell application” IEEE Trans. Electron Devices, 1984

› Challenges for screen printed and fired contacts: › “low values of silver-ink contact resistance..” › “..Good mechanical adhesion and solderability..” › “..High silver-ink conductivity..” › “..a minimum amount of silver penetration into the silicon surface..”

CONTACT FORMATION

Metallization workshop 2017, Konstanz | Matthias Hoerteis | Sabrina Werner et al. / Energy Procedia 124 (2017) 936–946

› Challenges for screen printed and fired contacts: › “low values of silver-ink contact resistance..” › “..Good mechanical adhesion and solderability..” › “..High silver-ink conductivity..” › “..a minimum amount of silver penetration into the silicon surface..”

CONTACT FORMATION

Metallization workshop 2017, Konstanz | Matthias Hoerteis | Zhang Yi – This Workshop

› Challenges for screen printed and fired contacts: › “low values of silver-ink contact resistance..” › “..Good mechanical adhesion and solderability..” › “..High silver-ink conductivity..” › “..a minimum amount of silver penetration into the silicon

surface..”

CONTACT FORMATION


Opening of SiN

REVIEW - CONTACT FORMATION - REACTIONS


Jeremy D. Fields, et al. DOI: 10.1038/ncomms11143 (2016)

2𝑃𝑃𝑃 + 𝑆𝑆𝑁𝑥 → 2𝑃𝑃 + 𝑆𝑆𝑃2 + 𝑥2𝑁2

𝑆𝑆𝑁𝑥 + 2𝐴𝐴2𝑃 → 𝑆𝑆𝑃2 + 4𝐴𝐴 + 𝑥2𝑁2

Bo-Mook Chung, Electrochimica Acta 106 (2013)

Gunnar Schubert, Solmat, Vol. 90, Issues 18-19, (2006)

Opening of SiN

REVIEW -CONTACT FORMATION - REACTIONS


Jeremy D. Fields, et al. DOI: 10.1038/ncomms11143 (2016)

Formation of Ag-crystallites

Kyoung-Kook Hong, Met. Mater. Int., Vol.15, No. 2 (2009)

4𝐴𝐴 + 𝑃2 → 4𝐴𝐴 𝑔𝑔𝑔𝑔𝑔+ + 2𝑃(𝑔𝑔𝑔𝑔𝑔)

−2

4𝐴𝐴 𝑔𝑔𝑔𝑔𝑔+ + 2𝑃(𝑔𝑔𝑔𝑔𝑔)

−2 + 𝑆𝑆 → 4𝐴𝐴0 + 𝑆𝑆𝑃2(𝑔𝑔𝑔𝑔𝑔)

𝐴𝐴 𝑔𝑔𝑔𝑔𝑔+ + 𝑒− → 𝐴𝐴0

2𝑃𝑃𝑃 + 𝑆𝑆𝑁𝑥 → 2𝑃𝑃 + 𝑆𝑆𝑃2 + 𝑥2𝑁2

𝑆𝑆𝑁𝑥 + 2𝐴𝐴2𝑃 → 𝑆𝑆𝑃2 + 4𝐴𝐴 + 𝑥2𝑁2

Bo-Mook Chung, Electrochimica Acta 106 (2013)

Gunnar Schubert, Solmat, Vol. 90, Issues 18-19, (2006)

› samples: n-PERT cell precursors › front and rear: H-pattern grid › Paste: SOL9620A (Standard Ag paste) › Co-firing of front and rear grids › In an RTP furnace

CONTROL ELECTRONS AT THE INTERFACE


Chanseok Kim DOI: 10.1038/srep21553 (2016)

Contact resistivity as a function of induced current

› At negative current (electrons are abandoned form contact formation) ρc >> 1 Ωcm²

› Large spread in contact resistance for 0 A known difficulties for pure Ag paste to contact boron emitters

› Contact resistances of < 5 mΩcm² for positively charged bias

CONTROL ELECTRONS AT THE INTERFACE


Guide to the eye -1.6A

0A 1.1A

MICROSTRUCTURE OF CURRENT INJECTED SAMPLES

-1.6A Electrons not available

0A Standard conditions

+1.1A Electrons are provided


› With increasing current, number of provided electrons, the number and density of Ag crystallites is growing


-1.6A Electrons not available

0A Standard conditions

+1.1A Electrons are provided


› With increasing current, number of provided electrons, the number and density of Ag crystallites is growing › The reaction of glass with the SiN layer seems not to be affected by the injected current

› The reaction of glass with the SiN layer seems not to be affected by the injected current

› EDX data comparing passivated areas (off) with contact areas (on)



CellIDOn/Off FL

12V, 3.8A12V, 1A12V, 1.1A12V, -1.6A0V, 0AonoffonoffOnoffOnoffOnoff

25

20

15

10

5

N

2

4.35

19.78

4.54

20.13

3.187

17.97

5.32

20.64

4.08

20.21

Individual Value Plot of N

INFLUENCE OF CONTACT CHEMISTRY

Experiment: › Wafer: Cz industrial precursors › Paste: Level of PbO in glass-system (IRS) was

changed

› Printed solar cells were fired and characterized

› IV, TLM



Name P1 P2 P3 PbO/IRS [wt%] 71% 65% 53%


changed


› IV, TLM




19.0

18.9

18.8

18.7

78.8

78.6

78.4

78.2

78.0

0.0056

0.0054

0.0052

0.0050

58P558P458P358P258P1

0.642

0.640

0.63858P558P458P358P258P1

0.350

0.325

0.300

0.275

0.250

58P558P458P358P258P1

18

15

12

9

6

Eta FF Rs

Voc J01 J02

18.9

496

18.8

379

18.7

871

18.7

406

18.7

022

78.5

821

78.3

404

78.2

423

78.3

675

78.1

963

0.00

5228

59

0.00

5291

9

0.00

5306

84

0.00

5229

9

0.00

5294

3

0.64

1966

0.64

0662

0.64

0026

0.63

9148

0.63

9295

0.33

6002

0.28

4155

0.30

4426

0.28

1528

0.29

5471

7.13

632

11.9

239

12.3

043

14.0

005

13.6

824

P1 P2 P3 P1 P2 P3 P1 P2 P3


changed


› IV, TLM

› Rs and ρc are not changed › Voc is increased while jo2 is reduced




19.0

18.9

18.8

18.7

78.8

78.6

78.4

78.2

78.0

0.0056

0.0054

0.0052

0.0050

58P558P458P358P258P1

0.642

0.640

0.63858P558P458P358P258P1

0.350

0.325

0.300

0.275

0.250

58P558P458P358P258P1

18

15

12

9

6

Eta FF Rs

Voc J01 J02

18.9

496

18.8

379

18.7

871

18.7

406

18.7

022

78.5

821

78.3

404

78.2

423

78.3

675

78.1

963

0.00

5228

59

0.00

5291

9

0.00

5306

84

0.00

5229

9

0.00

5294

3

0.64

1966

0.64

0662

0.64

0026

0.63

9148

0.63

9295

0.33

6002

0.28

4155

0.30

4426

0.28

1528

0.29

5471

7.13

632

11.9

239

12.3

043

14.0

005

13.6

824

P1 P2 P3 P1 P2 P3 P1 P2 P3

› PL (Voc) images of the test structure:

› Firing peak temperature: › 830°C › 850°C (ISC’s optimum) › 870°C

› Emitter: › Emitter 1 = 88 ± 5 Ω/sq › Emitter 2 = 99 ± 9 Ω/sq

J0,MET ANALYSIS USING PHOTO LUMINESCENCE (PL)


SOL9641B P1 P2 P3 SiO2/SiNx n+ emitter

p-type (2 Ωcm)

Corrado Comparotto, 2CV.2.23 PVSEC Amsterdam, 2017 Haifeng Chu, this workshop

J0,MET ANALYSIS USING PHOTO LUMINESCENCE (PL)


Summary of J0,met results › Strong dependency on firing temperature independent on

the paste chemistry › Reduced recombination values for pastes with lower lead

concentration

750775

800

825

850

875

900

925

950

975

1000

1025

1050

1075

1100

1125

1150

1175

1200

1225

1250

P1 P2 P3 R

Paste

Firing temperature (°C)

830

850

870

SOL9641B

MICROSTRUCTURE – CHANGED CHEMISTRY

Sample P1 fired at 850°C Sample P2 fired at 850°C Sample P3 fired at 850°C


› Very similar microstructure for all samples › Minor effect on crystallite size or density › Impact on j0met not clear

MICROSTRUCTURE – DIFFERENT FIRING TEMPERATURE

Sample P2 Fired at 830°C




› Differences in microstructure are clearly visible › Increasing number of Ag crystals with temperature › Number and size of Ag crystals affects J0met

› Electrons are playing a crucial role in contact formation › It is possible to manipulate the contact resistance by

providing or restricting electrons › PL is a powerful tool can be used to further and faster

understand contact recombination's › Understanding of contact microstructure and its influence on

jomet is the key to improve the Voc of printed and fired solar cells

CONCLUSION


THANK YOU

Haifeng Chu, Valentin D. Mihailetchi, Jens Theobald, Jan Lossen

Gregg Becht, Lindsey Karpowich, Ryan Mayberry

CONTACT RECOMBINATION AND MICROSTRUCTURE EVALUATION OF ... · the paste chemistry › Reduced...

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