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Solar cell metallization by laser transfer of
metal micro‐droplets
Michael Zenou1,2 ,Lee Bar‐On2 , Amir Saar2 and Zvi Kotler1
1‐AdditiveManufacturing Group, Orbotech ltd, Israel2‐ Racah Physics Institute, Hebrew University , Israel
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Presentation Content
• Introduction Of Laser Induced Forward Transfer (LIFT)
• Novel LIFT method TIN –LIFT. • TIN‐LIFT printed contact on silicon• Application to solar cells• Conclusion
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LASER INDUCED FORWARD TRANSFER
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J. Bohandy, B. F. Kim, and F. J. Adrian, “Metal deposition from a supported metal film using an excimer laser”, J.Appl.Phys, 60 (1986)
Transparent Substrate
Transferred Materials
Laser Absorption and local heating
DonorDonor
AcceptorAcceptor
Laser Induced Forward Transfer (1986)
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Hole Size in the donor
Focus Spot Size
Transferred Material size
A large range of materials:Ti , Al, Ni, Refractory metal, Organic material ,multi‐layer…
Advantages : large range of materials, resolutionsDisadvantages : printing quality, close contact
High horizontal Resolution
Bad printing quality:adhesion, pixel
interconnection, debris ...
Microscope picture of printed line
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LIFT allows transfer of micro‐droplet(2005)
Melting of the layer during the pulse
width
[3] David A. Willis and Vicentiu Grosu , “Microdroplet deposition by laser‐induced forward transfer”, Appl. Phys. Lett. 86, 244103 (2005)
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Good contact quality
Advantages : large range of materials, sub‐spot resolutionprinting quality.
Disadvantage : close contact, reactive material
Hole Size in the donor
Focus Spot Size
Transferred Material size
Sub‐spot size resolutiondrop >150 nm was demonstrated Droplet position accuracy
Donor needs close contact
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MainDespite LIFT’s advantages, limited utilization in industrial process
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No directing force to maintain accuracy
Liquid pool of the metal
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THERMAL INDUCED NOZZLE FORMATION‐LIFT
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Thermal Induced Nozzle (TIN‐LIFT)
hm=Materials Thickness
hp=Heated Zone during the pulse width
Self Nozzle formed during printing
Heat propagation
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SEM picture of the donor and the droplet
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Print quality dependence on the gap size
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Printed Aluminum patterns on different type of Substrate
GlassGlass PaperPaper
PET PET
Donor thickness = 500nm Gap = 300 mHorizontal resolution =10 m
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TIN‐LIFT PRINTED CONTACT ON SILICON
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Direct contact formation during the printing process
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Contact characteristic measurement method
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P‐type wafer
IV curve of the LIFT printed contact vs. the pulse energy
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Specific contact resistivity Specific contact resistance measured by TLM• p m‐Si: ρ
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APPLICATION TO SOLAR CELLCONNECTION OF HIGH VOLTAGE CELLS
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High Voltage Solar Cell on SOI wafer
40 µm
10 µm
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Metallization path
p type
p type
n type
n type
single solar cell
Metal Bridge
Metal Bridge
Metal BridgeConnection
Pad
Metal Bridge
ConnectionPad
ConnectionPad
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Metallization with TIN‐LIFT of aluminum
Before MetallizationBefore Metallization After MetallizationAfter MetallizationLine width of 10 µm
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IV curve for two rows of diodes connected in a series
IV
η1row= 6.7 %η2row= 6.4 %
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CONCLUSION
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LIFT of micro‐droplet advantages
Non‐Contact and Mask less
printing method
High horizontal resolution
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Conclusion
• We show a novel LIFT method:1‐ it allow printing at higher gaps.2‐ high horizontal resolution. • Printing of metal micro‐droplets provide a direct contact formation .
• We demonstrate the metallization technique on vertical solar cell on chip.
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Contact Detail :
micha‐[email protected]