6th metallization workshop single print metal stencils for ...€¦ · institute for solar energy...

Single print metal stencils for high-efficiency PERC

solar cells

H. Hannebauer1, T. Falcon2, J. Cunnusamy2, T. Dullweber1

1Institute for Solar Energy Research Hamelin (ISFH) 2ASM Alternative Energy

6th Metallization Workshop

Institute for Solar Energy Research Hamelin

Screen-printing is still the mainstream technique for front side metallization

Motivation

V. Shanmugam et al., IEEE Journal of Photovoltaics 5 (2), (2015), p. 525-533

Stencil-printing provides improved Ag finger profiles

Stencil-printing increases the conversion efficiency for narrow finger opening

Motivation

H. Hannebauer et al., Proc 5th Metallization Workshop, Energy Procedia 67, (2015), p. 108-115

Stencil-printing can reduce the silver finger paste consumption

Stencil Printed Ag Finger

A stencil features 100% open area in the aperture which leads to a benefit of excellent line height uniformity.

Width = 28 µm Height = 20 µm

Comparing screen and stencil technology

30 µm

• Stencil opening of 25 µm in combination with specific stencil Ag paste

• Two printing steps required for H-pattern design with stencil print for Ag fingers

• Novel Single Print Stencil combines advantage of one process step and excellent finger profiles

Screen Stencil

• VectorGuard Single Print Stencil prototype from ASM Alternative Energy

• Two layer metal foil; each layer being fabricated seperately

• Strong bond between two layers of nickel forming a single foil

• Top layer has a mesh grid over the busbar regions which acts as a bridge

• Finger regions are 100% open and fully stencil thickness

ASM AE VectorGuard Single Print Stencil prototype

Busbar

Finger

• Single Print (1x Print + 1x Dry)

• Dual Print (2x Print + 2x Dry)

+

Experiment plan

1st print: Screen 2nd print: Screen or Stencil

Screen or Stencil

Split groups of the experiment

Standard rectangular shaped five busbars in groups 1+3+4

Segmented five busbars with pads in group 2

Metal squeegee for stencils, polyurethane squeegee for mesh screens

Group Printing technique

Type of finger print

Ag finger aperture

[µm]

Ag paste

Finger paste consumption

[mg]

Busbar paste consumption

[mg]

Front Ag paste consumption

[mg]

1 Dual Print Stencil 30 A 86.0 14.2 100.2

2 Single Print Stencil 30 A - - 112.8

3 Dual Print Screen 40 B 59.9 14.2 74.1

4 Single Print Screen 40 B - - 91.5

Avg height = 12 µm Avg height = 22 µm Avg width: 47 µm Avg width: 36 µm

Impact of printing parameters on front grid resistance

Screen Stencil

Lf

ffinger r

AR =

ρ~Contribution of Ag finger to series resistance:

cmr screenL

Ω= 06.1, cm

r stencilLΩ

= 63.0,

0.05 Ωcm² increased Rs for screen-printing

ISFH PERC solar cell process

Rear protection layer

Texturing

Phosphorus diffusion

PSG + dielectric etch

Rear: AlOx/SiNy

Front: PECVD-SiNx

LCO at the rear

Al rear side metallization

Ag front side metallization

Co-firing

Wafer cleaning

PERC solar cell results

• Almost identical η for DP and SP with stencil finger print

PERC solar cell results

• Almost identical η for DP and SP with stencil finger print

• Voc gain for DP with non-firing through Ag busbar paste

PERC solar cell results

• Almost identical η for DP and SP with stencil finger print

• Voc gain for DP with non-firing through Ag busbar paste

• Jsc difference caused by 0.5%abs larger metallization area of screen print

PERC solar cell results

• Almost identical η for DP and SP with stencil finger print

• Voc gain for DP with non-firing through Ag busbar paste

• Jsc difference caused by 0.5%abs larger metallization area of screen print

• High conversion efficiency of 21.1% with novel single print stencil prototype on PERC solar cells achieved

• Single print stencil process saves one process step compared to dual print using a stencil while obtaining the same PERC cell performance

• Stencil print shows efficiency gain of 0.2%abs compared to today´s industrial screen print processes

Summary

We thank the German Federal Ministry for Economic Affairs and Energy

for funding part of this work under contract no. 0325753D (HighPERC) in

cooperation with

Acknowledgement