1 hoornstra konstanz presentation compress2

8/6/2019 1 Hoornstra Konstanz Presentation Compress2

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www.ecn.nl

Constance, April 20102nd Metal Workshop

Thick Film Printing:Towards Fine Line High Aspect Ratio

Jaap Hoornstra and Benot Heurtault


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+0.4% absoluteefficiency gainthrough FLHAR

Jsc[mA/cm]

Screen Stencil

Means and 95.0 Percent LSD Intervals

34.1

34.3

34.5

34.7

34.9

35.1

Voc[V]

Screen Stencil610

611

612

613

614

615(X 0.001)

FF[-]

Screen Stencil774

775

776

777

778

779(X 0.001)

Eta

[%]

Screen Stencil16.2

16.3

16.4

16.5

16.6

16.7

Hamburg,24th PVSEC, 2009

Average cell results: screen vs stencil


Improved cell efficiency with stencil


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Stencil printing

75m130m

Fired line width comparison

Screen printing

Print results



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Average print results

-100 -50 0 50 100

-5

0

5

10

15

20

25

30

35

Lin

eHeight(m)

Line Width (m)

Screen printing

Stencil printing

Width(m) Max Height(m) Min Height(m) avg Height(m)

Cross

section(um2) Rline (m/cm)

Screen 130 19 15 17 1300 180

Stencil 75 30 27 28 1500 150



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Scope: Towards FLHAR printing

What are settings of thick film

-Evolution front side metallization

-Landscape of thick film printing

Influencing parameters for FLHAR

-Look at details

- Identify challenges


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Evolution of front side & grid

H-pattern rulesMore demand on gridFLHAR important

6Constance, April 20102nd Metal Workshop


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Evolution of front side & grid

Courtesy Solland

Courtesy Photovoltech

MWT cells: FLHAR remains


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ECN PUM


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Thick film screen printingDominant technology

Estimated 85% of today cellmanufacturing

Metal mesh with emulsion = maskCourtesy of Koenen.de



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Thick film stencil printingA variation

Metal mask: various types and materials- Full metal: laser cut, electroformed, etched

- Hybrid: metal with emulsion, metal with metal mesh

- Single layer or two layers

NB-T: Sunstence Faithful E-stencil DEK hybrid screenLaser cut


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Why did screen printing emerge?

Simple process to create conductive pattern with functional material

-Flexible, allows various patterns

- One print stroke for full pattern

- Conductive paste: high mass loading metal in dispersion

Available and experience rely on electronic industry

- Glass fritted pastes from worked with little adoptions, fitted to co-firing, and even allowed firing through SiN

Robust process, high throughput, cost-effective

Challenges: wide fingers, conductivity, Rc


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SpreadingPaste flow behavior

Current measure:

-Single point viscosity data

Better:

-Dynamic measurement todescribe viscous andelastic behaviour

-Time dependent

oscillation rheometry

Viscosity as function of printing


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SpreadingRheological signaturepaste recovery


-100 -75 -50 -25 0 25 50 75 100-5

0

5

10

15

20

25

30

35

LineHeight(m)

Line Width (m)

Paste 1

Paste 2

Paste 3

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.0045.00

50.00

55.00

60.00

65.00

70.00

75.0080.00

85.00

90.00

50 100 150 200 250 300

Time [s]

Lossangle[]

Paste 1 Paste 2 Paste 3

Loss angle = arc tan G''/G

G' viscous componentG elastic componentG: paste freezes

40.00

41.00

42.00

43.00

44.00

45.00

46.00

47.00

48.00

49.00

50.00

100 101 102 103 104 105

Loss

angle

[]

Good correlation between paste recovery

and print results


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SpreadingInfluence of substrate

Foot print 15m wider on SiNx surface Influence of wetting by SiNx coating and texture

SiNx coating Bare Si

-5.00

0.00

5.00

10.00

15.00

20.00

25.00

30.00

-100.00 -80.00 -60.00 -40.00 -20.00 0.00 20.00 40.00 60.00 80.00 100.00

Width [m]

Height[m]

SiNx coating

Bare Si


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Wider fingersBleeding

Paste bleed also induce spreading


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Wider fingersBleeding and smearing


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Rounded emulsion


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Wider fingersSolvent bleeding


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Paste separationSolvent bleed

1mm

After printing Time lapse close-up


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Wider fingersSeparation bleed avalanche


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Squeegee

pressure


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Wider fingersBleeding vs. relative mesh opening



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Wider fingersBleeding vs. relative mesh opening

0 10000 20000 30000 40000 50000

-20

0

20

40

60

80

100

120

140

160

180

200

Grayv

alue

Distance (pixels)

Screen

Finger---Relative mesh opening

---Finger width



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In conclusion

FLHAR is here to stay

Thick film printing has still ability to comply Challenges and opportunities:

-Decrease paste spreading

- Improve on rheology-Work on bleeding

-Control wetting

-Control dispersion


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Latest resultsStencil printed seed layer

-5

0

5

10

15

20

-100 -50 0 50 100

Line width (m)

Lin

eheight(m)

-5

0

5

10

15

20

-100 -50 0 50 100

Line width (m)

Lin

eheight(m)

-5

0

5

10

15

20

-100 -50 0 50 100

Line width (m)

Lin

eheight(m)

--- Seed layer

--- Double print

--- Screen printing reference

40m

130m


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Thank you


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