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©Fraunhofer ISE/Foto: Guido Kirsch
© Fraunhofer ISE
Resist-free and Busbar Compatible Plating Route on TCOs Developed on SHJ Solar Cells
Thibaud Hatt, Jonas Bartsch, Sven Kluska and Markus Glatthaar
Fraunhofer Institute for Solar Energy Systems ISE, Freiburg – Germany
9th Metallization & Interconnection Workshop 2020
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High-efficiency potential of SHJ solar cells
Kaneka in 2015 h = 25.1% (Cu on front-side, busbars) [1]
Hanergy in 2020 h = 25.1% (Ag both-sides, busbar-less) [2]
Motivation Silicon Heterojunction Solar Cells
T. Hatt et al., 9th Metallization and Interconnection Workshop, 2020
[1] D. Adachi et al., Appl. Phys. Lett., vol. 107, no. 23, 2015. [2] X. Ru et al., Sol. Mat., vol. 215, p. 110643, 2020.
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High-efficiency potential of SHJ solar cells
Kaneka in 2015 h = 25.1% (Cu on front-side, busbars) [1]
Hanergy in 2020 h = 25.1% (Ag both-sides, busbar-less) [2]
Motivation Silicon Heterojunction Solar Cells
Why Cu-plating as low-T° metallization? Performance Conductiv ity , adhesion, contact res istiv ity…
Cost raw material Cu (dividing Ag price by factor > 100) [3]
Module-interconnection Versatile (BB-soldering / ECA / SWCT / Shingling…)
PV future (TW-scale) By 2030 might exceed Ag worldwide production [4-5]
Cuplated @ Fh-ISE
10 µm
T. Hatt et al., 9th Metallization and Interconnection Workshop, 2020
[1] D. Adachi et al., Appl. Phys. Lett., vol. 107, no. 23, 2015. [2] X. Ru et al., Sol. Mat., vol. 215, p. 110643, 2020. [3] S. Kluska et al., PV Inter. vol. 44, 2020.
[4] N.M. Haegel, Science, 364, 836–838, 2019. [5] P.J. Verlinden, 2.0 TW Workshop, Denver, USA 2018.
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Cu-plated metallization on TCOs
Several plating approach (different mask, seed-layer on TCO, mono/bifacial plating…) [5-6]
Resist masking on PVD metal-seed high h of 24.7% with busbars [6]
Challenge by copper plating TCOs masking
[5] T. Hatt et al., Sol. RRL, vol. 26, p. 1900006, 2019. [6] A. Lachowicz et al., 8th MIW, 2019. T. Hatt et al., 9th Metallization and
Interconnection Workshop, 2020
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Cu-plated metallization on TCOs
Several plating approach (different mask, seed-layer on TCO, mono/bifacial plating…) [5-6]
Resist masking on PVD metal-seed high h of 24.7% with busbars [6]
„NOBLE“ approach @ Fh-ISE [5]
Resist-free (patterning 5% cell area)
Simultaneous bifacial plating
Low contact resistivity
High adhesion
Challenge by copper plating TCOs masking
[5] T. Hatt et al., Sol. RRL, vol. 26, p. 1900006, 2019. [6] A. Lachowicz et al., 8th MIW, 2019. T. Hatt et al., 9th Metallization and
Interconnection Workshop, 2020
*NOBLE Native Oxide Barrier Layer for selective Electroplating
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Multi-task PVD metal stack on TCO
Plating mask Al + native AlOx
Homogeneous current distribution simultaneous bifacial plating
PVD TCO/Metals (Al on top) Characteristics
T. Hatt et al., 9th Metallization and Interconnection Workshop, 2020
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Multi-task PVD metal stack on TCO
Plating mask Al + native AlOx
Homogeneous current distribution simultaneous bifacial plating
Performance of PVD TiW or Ti as contacting layer on ITO [7]
Low contact resistivity ρc ≤ 1 mΩcm²
Ti TiW
0.1
0.5
1.0
2.0
3.0
4.05.0
10.0
Conta
ct
resis
itiv
ity ρ
c [
mΩ
cm
²]
Contacting metal-layer on ITO
PVD TCO/Metals (Al on top) Characteristics
[7] T. Hatt al., 47th IEEE-PVSC, 2020. T. Hatt et al., 9th Metallization and
Interconnection Workshop, 2020
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Multi-task PVD metal stack on TCO
Plating mask Al + native AlOx
Homogeneous current distribution simultaneous bifacial plating
Performance of PVD TiW or Ti as contacting layer on ITO [7]
Low contact resistivity ρc ≤ 1 mΩcm²
High adhesion > 2 N/mm (busbar peel test 90°)
PVD metal stack selectively etch-back [5]
PVD TCO/Metals (Al on top) Characteristics
[5] T. Hatt et al., Sol. RRL, vol. 26, p. 1900006, 2019. [7] T. Hatt al., 47th IEEE-PVSC, 2020.
Ti TiW
0.1
0.5
1.0
2.0
3.0
4.05.0
10.0
Conta
ct
resis
itiv
ity ρ
c [
mΩ
cm
²]
Contacting metal-layer on ITO
T. Hatt et al., 9th Metallization and Interconnection Workshop, 2020
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Patterning by inkjet-printing of etchantaq
Wetting on Al/AlOx
Grid patterning Al/AlOx local removal by inkjet-printing
T. Hatt et al., 9th Metallization and Interconnection Workshop, 2020
Al/AlOx
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Patterning by inkjet-printing of etchantaq
Wetting on Al/AlOx atmosphere / time dependent [8]
Adsorption alkyl molecules
Grid patterning Al/AlOx local removal by inkjet-printing
[8] T. Hatt et al., 9th SiliconPV, 2019.
5 days
T. Hatt et al., 9th Metallization and Interconnection Workshop, 2020
Al/AlOx
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Patterning by inkjet-printing of etchantaq
Wetting on Al/AlOx atmosphere / time dependent [8]
Chemical functionalization of Al/AlOx with self-assembled monolayer (ODPA) [9]
Adsorption by condensation reaction or ionic attraction on Al2O3
[10]
Grid patterning Al/AlOx local removal by inkjet-printing
[8] T. Hatt et al., 9th SiliconPV, 2019. [9] T. Hatt et al., submitted, 2020. [10] P. Thissen et al., ACS Langmuir, vol. 26, no. 1, pp. 156–164, 2010.
T. Hatt et al., 9th Metallization and Interconnection Workshop, 2020
ODPA: octadecyl-phosphonic acid
PO
OHOH
(ODPA)
Al/AlOx
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Patterning by inkjet-printing of etchantaq
Wetting on Al/AlOx atmosphere / time dependent [8]
ODPA functionalization of Al/AlOx (ODPA) [9]
FTIR-ATR measurements on native AlOx
Vibration of CH2 / CH3 ≈ 2900 cm-1
Vibration of P=O ≈ 1100 cm-1
Grid patterning Al/AlOx local removal by inkjet-printing
[8] T. Hatt et al., 9th SiliconPV, 2019. [9] T. Hatt et al., submitted, 2020.
T. Hatt et al., 9th Metallization and Interconnection Workshop, 2020
ODPA: octadecyl-phosphonic acid
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Patterning by inkjet-printing of etchantaq
Wetting on Al/AlOx atmosphere / time dependent [8]
ODPA functionalization of Al/AlOx (ODPA) [9]
FTIR-ATR measurements on native AlOx
Vibration of CH2 / CH3 ≈ 2900 cm-1
Vibration of P=O ≈ 1100 cm-1
XPS measurements on native AlOx
C1s increase / O1s decrease
P2p difficult to observe due to Al2s
Grid patterning Al/AlOx local removal by inkjet-printing
[8] T. Hatt et al., 9th SiliconPV, 2019. [9] T. Hatt et al., submitted, 2020.
T. Hatt et al., 9th Metallization and Interconnection Workshop, 2020
ODPA: octadecyl-phosphonic acid
PO
OHOH
(ODPA)
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Patterning by inkjet-printing of etchantaq
Wetting on Al/AlOx atmosphere / time dependent [8]
ODPA functionalization of Al/AlOx (ODPA) [9]
FTIR-ATR measurements on native AlOx
XPS measurements on native AlOx
Contact angle (CA) measurements on textured SHJ cells
CA after 30s ≥ 115°
CA stabilized ≈ 135° (after ≈ 1-2 hours)
Grid patterning Al/AlOx local removal by inkjet-printing
[8] T. Hatt et al., 9th SiliconPV, 2019. [9] T. Hatt et al., submitted, 2020.
T. Hatt et al., 9th Metallization and Interconnection Workshop, 2020
ODPA: octadecyl-phosphonic acid
PO
OHOH
(ODPA)
No ODPA
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Patterning by inkjet-printing of etchantaq
Wetting on Al/AlOx atmosphere / time dependent [8]
Chemical functionalization of Al/AlOx with self-assembled monolayer (ODPA) [9]
Patterning of full area SHJ solar cells [9]
Grid patterning Al/AlOx local removal by inkjet-printing
[8] T. Hatt et al., 9th SiliconPV, 2019. [9] T. Hatt et al., submitted, 2020. T. Hatt et al., 9th Metallization and
Interconnection Workshop, 2020
*Cu / Al layers sputtered @
157 m
m Al/AlOx
Opened
Patterned solar cell ITO / Cu / Al50nm
Al/AlOx
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Patterning by inkjet-printing of etchantaq
Wetting on Al/AlOx atmosphere / time dependent [8]
Chemical functionalization of Al/AlOx with self-assembled monolayer (ODPA) [9]
Patterning of full area SHJ solar cells [9] microscopy (72 different spots)
Grid patterning Al/AlOx local removal by inkjet-printing
[8] T. Hatt et al., 9th SiliconPV, 2019. [9] T. Hatt et al., submitted, 2020. T. Hatt et al., 9th Metallization and
Interconnection Workshop, 2020
157 m
m
20 mm
Al/AlOx
10 f
ing
ers
Opened
Patterned solar cell ITO / Cu / Al50nm
25 µm
w l
Al/AlOx
Cu
25 µm
25 µm
w l
w l
*Cu / Al layers sputtered @
25 µm
Al/AlOx (not opened)
x50
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Patterning by inkjet-printing of etchantaq
Wetting on Al/AlOx atmosphere / time dependent [8]
Chemical functionalization of Al/AlOx with self-assembled monolayer (ODPA) [9]
Patterning of full area SHJ solar cells [9] microscopy (72 different spots)
Narrow to wide patterning on same wafer
Inhomogeneous even on same wafer
Grid patterning Al/AlOx local removal by inkjet-printing
[8] T. Hatt et al., 9th SiliconPV, 2019. [9] T. Hatt et al., submitted, 2020. T. Hatt et al., 9th Metallization and
Interconnection Workshop, 2020
*Cu / Al layers sputtered @
wl 72.7 ± 29.7 µm wl 44.0 ± 23.8 µm
No ODPA
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Patterning by inkjet-printing of etchantaq
Wetting on Al/AlOx atmosphere / time dependent [8]
Chemical functionalization of Al/AlOx with self-assembled monolayer (ODPA) [9]
Patterning of full area SHJ solar cells [9] microscopy (72 different spots)
Narrow patterning
Homogeneous on full wafer
Grid patterning Al/AlOx local removal by inkjet-printing
[8] T. Hatt et al., 9th SiliconPV, 2019. [9] T. Hatt et al., submitted, 2020. T. Hatt et al., 9th Metallization and
Interconnection Workshop, 2020
*Cu / Al layers sputtered @
wl 72.7 ± 29.7 µm wl 44.0 ± 23.8 µm
No ODPA
wl 26.9 ± 3.1 µm
With ODPA
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Selective Cu plating on metal-seed [8]
Homogeneous narrow fingers plated ≤ 30 µm [9]
Cu plating Selective deposition
[8] T. Hatt et al., 9th SiliconPV, 2019. [9] T. Hatt et al., submitted, 2020.
20 µm 20 µm
Al/AlOx
Metal-seed
Al/AlOx
Cu-plated
SEM picture
T. Hatt et al., 9th Metallization and Interconnection Workshop, 2020
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Selective Cu plating on metal-seed [8]
Homogeneous narrow fingers plated ≤ 30 µm [9]
Selective wet etch-back of PVD metal layers [5]
Cu plating and etch-back Selective
[5] T. Hatt et al., Sol. RRL, vol. 26, p. 1900006, 2019. [8] T. Hatt et al., 9th SiliconPV, 2019. [9] T. Hatt et al., submitted, 2020.
20 µm 20 µm
Al/AlOx
Metal-seed
Al/AlOx
Cu-plated
26 µm
SEM picture
T. Hatt et al., 9th Metallization and Interconnection Workshop, 2020
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Development of this novel metallization
Al patterning modification proof of concept
Upscaling on full area solar cells (M2)
Optimization of contacting layer and ρc
SHJ solar cells efficiency „NOBLE“ metallization
*NOBLE Native Oxide Barrier Layer for selective Electroplating
T. Hatt et al., 9th Metallization and Interconnection Workshop, 2020
[3] S. Kluska et al., PV Inter. vol. 44, 2020. [5] T. Hatt et al., Sol. RRL, vol. 26, p. 1900006, 2019 [7] T. Hatt al., 47th IEEE-PVSC, 2020. [8] T. Hatt et al., 9th SiliconPV, 2019.
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Development of this novel metallization
Al patterning modification proof of concept
Upscaling on full area solar cells (M2)
Optimization of contacting layer and ρc
Optimization of inkjet-printing patterning with SAM
SHJ solar cells efficiency „NOBLE“ metallization
Both SHJ cells no light soaking
*NOBLE Native Oxide Barrier Layer for selective Electroplating
[3] S. Kluska et al., PV Inter. vol. 44, 2020. [5] T. Hatt et al., Sol. RRL, vol. 26, p. 1900006, 2019 [7] T. Hatt al., 47th IEEE-PVSC, 2020. [8] T. Hatt et al., 9th SiliconPV, 2019.
Area [cm²]
Voc [mV]
pFF [%]
FF [%]
Jsc [mV]
Rs [Ωcm²]
η [%]
222* 736 84.8 81.3 37.9 0.5 22.7
RefSP 735 84.6 81.5 38.3 0.7 22.9
T. Hatt et al., 9th Metallization and Interconnection Workshop, 2020
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Summary Novel Cu-metallization
NOBLE metallization on TCOs for SHJ solar cells
Simultaneous bifacial Cu-plating
Low-cost – no resist, only grid-area to be patterned
TCO + Metal stack PVD tool
Al-patterning Inkjet-printer
Cu-plating + etch-back Wet chemical baths
T. Hatt et al., 9th Metallization and Interconnection Workshop, 2020
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Summary Novel Cu-metallization
NOBLE metallization on TCOs for SHJ solar cells
Simultaneous bifacial Cu-plating
Low-cost – no resist, only grid-area to be patterned
Inkjet-printing patterning optimized
Chemical functionalization of Al/AlOx surface with SAM
Characterization of the fast ODPA adsorption
Homogeneous fine patterning ≤ 30µm wide
Successful transfer to large area SHJ solar cells (M2)
η 22.7% on large area with FF > 81% and Rs < 0.5 Ω∙cm²
TCO + Metal stack PVD tool
Al-patterning Inkjet-printer
Cu-plating + etch-back Wet chemical baths
T. Hatt et al., 9th Metallization and Interconnection Workshop, 2020
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Acknowledgment The authors would like to thank …
…the Fraunhofer society for funding within the project “LEO” (contract no. 840 190)
…all co-workers at Fraunhofer ISE and VON ARDENNE for metal sputtering
…you for your attention!
Fraunhofer Institute for Solar Energy Systems ISE
Thibaud Hatt | Advanced Development for High Efficiency Silicon Solar Cells
T. Hatt et al., 9th Metallization and Interconnection Workshop, 2020