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Characterisation of Aluminium screen-printed local contacts · © Fraunhofer ISE 2 Agenda...
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© Fraunhofer ISE Characterisation of Aluminium screen-printed local contacts a,b F. S. Grasso, a L. Gautero , a J. Rentsch, b R. Lanzafame a Fraunhofer Institute for Solar Energy Systems ISE b Dipartimento di Ingegneria Industriale e Meccanica, Faculty of Engineering, University of Catania, Second Metallisation Workshop Konstanz, 14 . 04 . 2010
Transcript of Characterisation of Aluminium screen-printed local contacts · © Fraunhofer ISE 2 Agenda...
© Fraunhofer ISE
Characterisation of Aluminium screen-printed local contacts
a,bF. S. Grasso, aL. Gautero, aJ. Rentsch, bR. LanzafameaFraunhofer Institute for Solar Energy Systems ISEbDipartimento di Ingegneria Industriale e Meccanica, Faculty of Engineering, University of Catania,
Second Metallisation WorkshopKonstanz, 14 . 04 . 2010
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Agenda
Motivation
Approach of the characterisation
Results and first interpretation
Case Study: LFC contacts
Conclusions
Outlook
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Motivation
Passivated Emitter and Rear Cell (PERC)
High potential : >23% in lab scale ()
Local Contacts
Passivated Emitter and Rear Cell (PERC)
High efficiency potential: >23%1
1Blakers et Al. 9th EUPVSEC, Freiburg, 1989
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Motivation
The Schottky barrier becomes Ohmic-like at High surface doping
High surface doping decreases recombination at metal contact32Yu, Solid State Electronics, 1970
3Altermatt, EUPVSEC, Hamburg, 2009
ρ clnρ c
FE (Field)
TFE (Thermionic Field)
TE (Thermionic)
Contact resistance dependency on Surface doping2
D
1N
Higher surface doping
FE
Schottkybarrier
Emissions
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Alloying model: Total Contact
From literature on alloying model4
4Huster, 20th EUPVSEC ,Barcelona, 2005
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Motivation
Modify, refit existing technology
Screen print
Passivation
Total surface contact Local surface contact
Out of scale
p type Silicon
p+ type Silicon
Aluminium/SiliconEutectic
AluminiumPaste
Passivation
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What is so hard in making local back surface contacts?
Examples of Aluminium to Silicon Contacts
Local surface contact – BAD exampleTotal surface contact
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Contact Sintering - Experimental
Surface structuring
Track amount of paste
Flat
Hollow
Process
Characterisation-+
OK!
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Contact Sintering - Experimental
Surface structuring
Track amount of paste
Flat
Hollow
Process
Characterisation-+
OK!
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Laser Firing - Experimental
Track amount of paste
Process
Characterisation-+
OK!
LFC
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Preparation- Experimental
Hollow Flat
KOH Etch
Dielectric deposition
Local Opening
KOH Etch
Surface structuring
Flat
Hollow
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Hollow Flat
KOH Etch
Dielectric deposition
Local Opening
KOH Etch
Preparation- Experimental
Passivation Layer
Flat Local Opening
~100µm
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Hollow Flat
KOH Etch
Dielectric deposition
Local Opening
KOH Etch
Preparation- Experimental
Tilted view of a hollow opening
The hollow is at maximum 10 μm deep
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Preparation- Experimental
Hollow Flat
KOH Etch
Dielectric deposition
Local Opening
KOH Etch
Amount of paste
LFC process as reference
Al Paste printing
Firing
LFC
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Hollow Flat
KOH Etch
Dielectric deposition
Local Opening
KOH Etch
Al Paste printing
Firing
Al removal
LFC
Approach – Optical characterisation
7.4 5±28
Max Depth(µm)
Paste amount
(mg/cm²)
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Hollow Flat
KOH Etch
Dielectric deposition
Local Opening
KOH Etch
Al Paste printing
Firing
Al removal
LFC
Approach – Optical characterisation
7.96.2
4±501±45
Max Depth(µm)
Paste amount
(mg/cm²)
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Approach – Optical characterisation
7.4 5±28
Max Depth(µm)
Paste amount
(mg/cm²)
7.96.2
4±501±45
Max Depth(µm)
Paste amount
(mg/cm²)
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Approach - Cross Sectioning and Stain Etch
Fired Al EutecticAl-BSF
6.2 mg/cm²
Stain etch is suitable due to the metallurgic junction of Aluminium doped Silicon4
5Huster, 20th EUPVSEC ,Barcelona, 2005
Total contact6.2 mg/cm² wet Al paste firing peak temperature 900 °C.
1E19
1E15
1E16
1E17
1E18
DepthCon
cent
ratio
n (c
m-3
)Metal Si
ECV Al doping meas.5
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Approach - Cross Sectioning and Stain Etch
Stain etch applied to local contacts
t etch = 80 s
local contact - Flat7.9 mg/cm² wet Al paste 109x102µm openingfiring peak temperature 900 °C.
20 μm
20 μm
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Approach - Cross Sectioning and Stain Etch
A. Fused Spherical particles
B. Lamellas
C. Surrounding BSF layer
D. Irregularities in the cavity
local contact - Hollow7.9 mg/cm² wet Al paste 109x102µm openingfiring peak temperature 900 °C.
HOLLOW
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Approach - Cross Sectioning and Stain EtchFused Spherical particles
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Approach - Cross Sectioning and Stain Etch
Lamellas
Lamellas
Lamellas
Fused Spherical particles
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Approach - Cross Sectioning and Stain Etch
Surrounding BSF layerSurro
unding BSF layer
Surrounding BSF layer
Lamellas
Lamellas
Lamellas
Fused Spherical particles
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Approach - Cross Sectioning and Stain Etch
Irregularities in the cavity
Lamellas
Lamellas
Lamellas
Fused Spherical particles
Surrounding BSF layerSurrounding BSF layer
Surrounding BSF layer
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Approach - Cross Sectioning and Stain Etch
Irregularities in the cavity
Lamellas
Lamellas
Lamellas
Fused Spherical particles
Surrounding BSF layerSurrounding BSF layer
Surrounding BSF layer
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Approach - Cross Sectioning and Stain Etch
local contact – Flat6.2 mg/cm² wet Al paste 109x102µm openingfiring peak temperature 900 °C.
540nm
FLAT
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Approach - Cross Sectioning and Stain Etch
Lamellas can be foundmore than 20µm away
from contactContactDielectric
20µm
local contact - Hollow7.9 mg/cm² wet Al paste 109x102µm openingfiring peak temperature 900 °C.
HOLLOW
Loss of -doped- Silicon
50µm
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Approach - Cross Sectioning and Stain Etch
Thick BSFThin BSF
No BSF
Fusion of Particles
Irregularities in the contact formation
local contact – Flat4.7 mg/cm² wet Al paste 109x102µm openingfiring peak temperature 900 °C.
FLAT
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Interpretation – Alloying model: Local contact
6. Si is expulsed, in forms of lamellas, wherever it is
1
Dry Al Paste
Si
DielectricT=RT
2T=660°C
3T=700°C
4T=825°C
5T=700°C
6T=577°C
5. Thin BSF formation
similar in Beaucarne, First WS Metallization, Utrecht, 2008
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Case Study: Laser Fired Contact on SP Aluminium
100µm
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Case Study: Laser Fired Contact on SP Aluminium
Thin BSF between resin and Silicon
Before stain etch After stain etch
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Case Study: Laser Fired Contact on SP Aluminium
1 2
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1. Carbon: due to the presence of the protective layer.
2. Oxygen
3. Aluminium
4. Silicon
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Conclusions
Surface doping is necessary for good contacts
A method has been developed to characterise doping on local contacts
First understanding of results of present state of art
Case Study showed the flexibility of the method
Process
Characterisation
-+
OK!
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Outlook
Different methods need to be developed to increase the statistical significance
Its characteristic are
More contacts at a time (averaging)
Less invasive (Optical, maybe PL/EL?)
More closely related to the functioning principle
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Special thanks go to
Federico Sebastiano Grasso,
Jan Nekarda,
Miroslawa Kwiatkowska,
Aleksander Filipovic
for the contribution to this work
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Thank you for your attention
Questions?
Luca Gautero
Fraunhofer-Institut für Solare Energiesysteme ISE
