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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
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
LASER INDUCED FORWARD TRANSFER
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)
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
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)
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
MainDespite LIFT’s advantages, limited utilization in industrial process
No directing force to maintain accuracy
Liquid pool of the metal
THERMAL INDUCED NOZZLE FORMATION‐LIFT
Thermal Induced Nozzle (TIN‐LIFT)
hm=Materials Thickness
hp=Heated Zone during the pulse width
Self Nozzle formed during printing
Heat propagation
SEM picture of the donor and the droplet
Print quality dependence on the gap size
Printed Aluminum patterns on different type of Substrate
GlassGlass PaperPaper
PET PET
Donor thickness = 500nm Gap = 300 mHorizontal resolution =10 m
TIN‐LIFT PRINTED CONTACT ON SILICON
Direct contact formation during the printing process
Contact characteristic measurement method
P‐type wafer
IV curve of the LIFT printed contact vs. the pulse energy
Specific contact resistivity Specific contact resistance measured by TLM• p m‐Si: ρ
APPLICATION TO SOLAR CELLCONNECTION OF HIGH VOLTAGE CELLS
High Voltage Solar Cell on SOI wafer
40 µm
10 µm
Metallization path
p type
p type
n type
n type
single solar cell
Metal Bridge
Metal Bridge
Metal BridgeConnection
Pad
Metal Bridge
ConnectionPad
ConnectionPad
24
Metallization with TIN‐LIFT of aluminum
Before MetallizationBefore Metallization After MetallizationAfter MetallizationLine width of 10 µm
IV curve for two rows of diodes connected in a series
IV
η1row= 6.7 %η2row= 6.4 %
CONCLUSION
LIFT of micro‐droplet advantages
Non‐Contact and Mask less
printing method
High horizontal resolution
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.
Contact Detail :
micha‐[email protected]