©Fraunhofer ISE/Foto: Guido Kirsch

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PROGRESS IN SHINGLE INTERCONNECTION BASED ON

ELECTRICALLY CONDUCTIVE ADHESIVES AT FRAUNHOFER ISE

Daniel von Kutzleben, Torsten Rößler, Nils Klasen,

Veronika Nikitina, Puzant Baliozian, Anna Münzer,

Esther Fokuhl, Achim Kraft

Fraunhofer Institute for Solar Energy Systems ISE

10th Metallization and Interconnection Workshop for

Crystalline Silicon Solar Cells

Genk (Belgium), 15.11.2021

www.ise.fraunhofer.de

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Introduction

Interconnection for integrated PV

Advantages of shingle interconnection [1]

Increased active module area

Absence of cell ribbons

Visual appearance

Process temperature < 200 °C

Lead-free

Matrix technology [2] has performance advantage with

partial shading [3,4]

Challenges/disadvantages

Losses caused by cell separation

New processes and module designs

Costs of electrically conductive adhesives (ECAs)

Schematic of shingle interconnection Shingle interconnection in PV

module

overlapped

shingle

Shingle strings in a curved car roof Shingle matrix interconnection

[1] D. C. Dickson, Patent no. US 2938938 A, 1960

[2] W. Schmidt et al., Trans. Electron Devices, 1990

[3] N. Klasen et al., submitted to IEEE Journal of Photovoltaics, 2021

[4] N. Klasen et al., EUPVSEC Conference Proceedings, 2021

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Production of shingle modules at Fraunhofer ISE

cell separation

ECA application

shingleplacement

ECAcuring

string end contact

string bussing

lamination

External laser tool

TT1600ECA M10 Industries stringer

[1]

M2 to M6 formats

Solder/ECA stringer

with shingle upgrade

Screen printing ECA

and IR-assisted hot

plate curing

Linear shingling

1600 shingles / hour

M2 to G12 formats

dispensing ECA and

IR-curing

linear shingling and

matrix technology

4000 shingles / hour

(lab type)

12000 shingles / hour

(industrial type)

[1] Sunpower Corp. Patents EP3489848, EP3149775, EP3506134

Other patent applicants/owners for process or module aspects: Applied

Materials, Tesla, Wuxi Autowell, Canadian Solar, Solaria

(list may be incomplete)

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Materials and processes in the experimental part

Industrial PERC shingle host wafers in M2 format

Separated by laser scribe and mechanical cleave

(LSMC) [1] to 31.35 mm shingles

ECA

Epoxy-based with a density of 1.9 g/cm³

Ag-fillers

Strings for full-scale modules produced at TT1600ECA

Dispensing variation by offline Musashi dispenser

Industrial mono PERC shingle host wafer (M2 format)

Microscopic cross section image of shingle bond

upper shingle

lower shingle

metallization

ECA

100 µm

[1] A. Münzer et al., EUPVSEC Conference Proceedings, 2020

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Shingle module design

Design guidelines

Maximizing use of glass

Limiting string voltage

Achieving reasonable module output characteristics

Restrictions due to patented module designs [1,2]

Dimensions

Non-optimal glass dimensions (1700 mm x 1000 mm)

Active module area = 86 %

31 cells per string

< 3 mg ECA per shingle joint, down holding in curing step

Module layout: two blocks with 5 parallel strings in series, split

junction box with bypass diodes

Encapsulant POE, back sheet PET/Al/PET

Front side Back side

10 S

trin

gs

string length = 932 mm

Uoc = 42 V

Isc = 9,5 A

[1] Sunpower, Patent EP3518126 (A1)

[2] The Solaria Corp., Pantent USD896167 (S)

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Shingle process optimization

ECA amount and downholding

TC50 TC200 TC400 TC50 TC200 TC400

5 m

g

3 m

g

1.3

mg

5 m

g

3 m

g

1.3

mg

5 m

g

3 m

g

1.3

mg

5 m

g

3 m

g

1.3

mg

5 m

g

3 m

g

1.3

mg

5 m

g

3 m

g

1.3

mg

no down holding down holding

-15

-10

-5

0

Po

wer

cha

ng

e (

%)

Three different application patterns and

ECA quantities

Continuous 5 mg

Dashed 3 mg

Dotted 1.3 mg

Two groups: with and without down holding

during the curing process

Use of a preheated curing oven for 10

minutes at 200 °C

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Shingle process optimization

Variation of curing temperature

Variation of curing temperature from

90 °C to 200 °C

Electrical performance of strings decreases

for curing temperatures below 130 °C

Similar effect observed if heating ramp is not

steep enough

90 100 110 120 130 140 150 160 170 180 190 200

4.8

4.9

5.0

5.1

5,07

T[°C]

Maxim

um

Pow

er

PM

PP [W

]

5 x Pmpp, shingle

5-cell-modules

5.7

T (°C)

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Losses and gains from host cell to module

Overview

Efficiency loss due to edge recombination [1]

GridTouch measurement of host cell without

influence of finger resistance

Busbar-to-busbar measurement of shingles and

in the string with influence of finger resistance

Further efficiency losses and gains during

module integration [2]

Dominant factor is glass margin

Efficiency gain by overlapping busbars

Host cell

Edge

recombination [1]

Finger

resistanceShingle

Module

Geometrical

losses/gains

Optical losses

and gains

Electrical

losses

Loss/gain factor

[1] P. Baliozian et al., IEEE Journal of Photovoltaics, 2020

[2] M. Mittag et al., IEEE PVSC Conference Proceedings, 2017

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-10 0 10 20 30 40 50 600

50

100

150

200

250

300

350

400

450

500

po

wer

loss

Plo

ss,f (

mW

)

current path in finger d (mm)

20,0

20,5

21,0

21,5

η (

%)

~30 µm

~50 µm

finger width

Finger resistance effect

„GridTouch“ vs. shingle in string

21.6% idealized host cell without finger resistance

GridTouch (GT) overestimates busbar-to-busbar

efficiency of shingle

Simulated busbar-to-busbar measurement (d ~ 30 mm)

yields (21.2 ± 0.1) %

Interconnection in the string is busbar to busbar

Simulated change of Eta = (−0.4 ± 0.1)%abs

from GT-measured host cell to shingle in the string

Depending on lateral finger resistance RLØ and

current path in finger d

d = 2.5 mm d = 30 mm

𝑅𝐿∅ = 0.88 Ω/cm [1]

𝑛𝑓 = 120

𝐼𝑓 = 17 mA

𝑅𝐿∅ = 0.56 Ω/cm

Simulation based on [1,2]

„GridTouch“

measurement

of host cell

Shingle string and

busbar-to-busbar

measurement

[1] A. Mette, Dissertation, University of Freiburg, 2007

[2] A. Lorenz et al., EUPVSEC Conference Proceedings, 2018

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73

74

75

76

77

78

79

80

81

82

83

fill f

act

or

FF (

%)

host cell shingle

19.0

19.5

20.0

20.5

21.0

21.5

22.0

eff

icie

ncy

η (

%)

host cell shingle

76

78

80

82

84

86

pse

ud

o f

ill fa

cto

r p

FF (

%)

shinglehost cell

0.4

0.6

0.8

1.0

1.2

1.4

seri

es

resi

stan

ce R

S (

Ωcm

²)

host cell shingle

Change from host cell to shingle

Experimental analysis

Measured efficiency change of −1.1%abs mainly

linked to FF −3.8% abs

Combined effect

Rs increase: finger resistance of

busbar-to-busbar measurement

pFF decrease: edge recombination

RS increase accounts for approx.

−1.1%abs FF and −0.3%abs efficiency **)

pFF decrease accounts for approx.

−2.7%abs FF and −0.8%abs efficiency **)

Can partially be regained by edge

passivation

finger

resistance

edge

recom-

bination

LSM

C

LSMC

*) *)

*) Corrected by finger length as in shingle

**) Uncertainty of values +/- 0.1%

improved

process

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Improving edge recombination

Passivated Edge Technology (PET)

Post-metallization/separation

Passivated edge technology (PET) [1,2]: Aluminum

oxide deposition and post-deposition annealing

Host cells measured and pFF values considered

Similar decrease in ΔpFF = −1.2%abs for TLS and

LSMC processes

Combination of deposition and annealing of TLS-

separated cells:

ΔpFF = +0.6%abs

Half of pFF loss regained (from separated state)81.5

82.0

82.5

83.0

83.5

84.0

84.5

85.0

85.5

Pse

ud

o-f

ill fa

cto

r p

FF

(%

)

LSMC TLS

82.5

83.0

83.5

84.0

84.5

85.0

85.5

Pse

ud

o-f

ill fa

cto

r p

FF

(%

)

Host wafer

pSPEER

As-deposited

Annealed

LSMC: laser scribe and mechanical cleave

TLS: Thermal laser separation

Shingle

22 mm x 148 mm bifacial PERC solar cells [1]

[1] P. Baliozian et al., IEEE Journal of Photovoltaics, 2020

[2] Patent DE 102018123485A1, 2020

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Shingle vs. module

Full-scale modules

Shingle-to-module efficiency loss −2.8%abs

Dominated by glass margin

Partially due to optical factors (e.g. reflection,

absorption) and light stabilization prior to

measurement

Shingle-to-module power loss of −2.6%rel

Improved module with 416 shingles yields

P = 412 Wp and η = 19.6%

Shingle-to-module fill factor loss ΔFF = −0.6%abs

Minor defects according to electroluminescence

Series resistance in string connection and cables

76,9

76,3

shingles modules

74,5

75,0

75,5

76,0

76,5

77,0

77,5

78,0

78,5

Fill fa

cto

r FF (

%)

20,5

17,7

shingles modules16,517,017,518,018,519,019,520,020,521,021,5

Eff

icie

ncy

η (

%)

«SmartCalc.CTM

312,0

303,7

shingles* modules

295

300

305

310

315

320

PM

PP (

W)

«Sm

artC

alc.CTM

9,66

9,53

shingles** modules9,4

9,5

9,6

9,7

9,8

I SC (

A)

*) individually measured shingle power × 310

**) individually measured shingle current × 5

412 W Module

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Full size reliability tests

306 W- 308 W

Hot spot test

302 W - 306 W 301 W - 305 W

300 W - 306 W

TC

20

0

DH

1000

Mechanical load testDH1000TC200

ΔP = +0.9%…+1,9%rel ΔP = -0.1%…+0.4%rel

p = 2400 Pa

p = 3500 Pa

ΔP = -0.4 %rel

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Summary

Shingling and matrix technology is a particularly suitable technology for integrated applications

Module design guided by max. string voltage, patents, maximizing use of glass

Full-size module production demonstrated with max. power 412 W and 19.6% efficiency

1.3 mg ECA per shingle joint possible when down holding used

Modules pass important reliability tests

Host cell to module effects

Host cell (GridTouch)

21.6%

finger length corrected

measurement

21.2...21.3%

non-optimized

LSMC

20.5...20.6%

5th shingle module

non-optimized

glass size and other

CTM effects

17.7...17.8%

TLS

20.9...21.0%

module

20.2...20.5%

improved edge

passivation (PET)

21.0...21.2%

improved glass

and CTM

Potentially

improved

route

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Thank You for Your Attention!

Daniel von Kutzleben

www.ise.fraunhofer.de

Daniel.von.kutzleben@ise.fraunhofer.de