evaluation of flexographic printing technology for multi...
TRANSCRIPT
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EVALUATION OF FLEXOGRAPHIC PRINTING TECHNOLOGY FOR MULTI BUSBAR SOLAR CELLS
A. Lorenza, A. Senneb, J. Rohdec, S. Kroha, M. Wittenberga, K. Krügera, F. Clementa, and D. Biroa
aFraunhofer ISE, FreiburgbContiTech Elastomer-Beschichtungen GmbH, Northeim
cZecher GmbH, Paderborn
Metallization WorkshopConstance, October 21st 2014
www.ise.fraunhofer.de
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MotivationSolar Cell Metallization Costs
Screen printing still state-of-the-art technology
Drawbacks: Limited throughput, cost-intensive screens, high silver consumption andlimited finger widths
Objectives: Higher throughput rates
Reduce costs of printing consumables
Reduce silver consumption
Reduce shading lossesShare of cell production costs without Si wafer calculated with CoO Calculation Tool SCost [1], Ag-Price 562.00 €/Kg, 14.10.2014. [1] S. Nold et al., 27th EU PVSEC 2012
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ApproachFlexographic Printing Technology
Front and rear side metallizationusing rotational printing
Flexography - relief printing technique, flexible printing plate
High-speed roll-to-roll machines used in package printing
FhG ISE and TU Darmstadt introduced this technology for Si solar cells in 2011 [2]
[2] M. Frey et al., Energy Procedia 11 (2011)
Flexographic printing platform for solar cell metallization
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TechnologyFlexographic Printing Technology
Significantly higher throughputthan screen printing possiblevFX 50 - 600 m/min.vSP 12 m/min.
Low costs of printing plates(10 – 25 € per plate)
Low amount of ink transferred
Approx. 7-10 mg Ag per Wafer
Thin layer thickness (2-4 µm)
SEM images of flexo double-printed contact finger (top) and screen printed contact finger (bottom)
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TechnologySeed & Plate vs. fully flexo printed Metallization
Flexo-printed seed layer + Light-induced plating (LIP) Solar cell results up to 18.8 %
demonstrated by ISE [3]
CoO-Calculation demonstratedconsiderable cost saving potential
Fully flexo-printed metallization Single or double printing
process
Highly interesting for Multi Busbar Solar cells
Solar cell with flexo printed seed layer front side metallization + Ag-LIP[3] A. Lorenz et al., JPMTR (2014)
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TechnologyFlexographic Printing Technology – Schematic
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TechnologyFlexographic Printing Technology – Schematic
500 µm
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TechnologyFlexographic Printing Technology – Schematic
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TechnologyFlexographic Printing Technology – Schematic
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TechnologyFlexographic Printing Technology – Schematic
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TechnologyElastomer Printing Plates
New Approach: Laser-engraved elastomer-based
Plates
Nominal widths down to wn 5 µm can be realized
Considerably longer operation time (than polymer plates)
Resistant against mostsolvents
Low costs per plate
Flexographic printing form with H-patterncell layout / SEM image of Finger-Busbar cross-section
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Experimental ApproachTest layout
Experimental approach: Test layout with finger elements
wn,min = 5µm to wn,max = 50 µm3 identical sections
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Experimental ApproachAnilox roll with differently engraved band sections
Experimental approach: Test layout with finger elements
wn,min = 5µm to wn,max = 50 µm3 identical sections
Evaluation of optimum anilox roll 3 band sections with differentdip volumes (in cm³/m²)
DHex1 = 11.8 cm³/m²
DHex2 = 8.7 cm³/m²
DSquare = 10.1 cm³/m²
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Experimental ApproachPrinting process
Experimental approach: Test layout with finger elements
wn,min = 5µm to wn,max = 50 µm3 identical sections
Evaluation of optimum anilox roll 3 band sections with differentdip volumes (in cm³/m²)
Double printing with intermediatedrying
Printed test form on silicon wafer during theexperiment
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Experimental ApproachOptical and electrical characterization
Experimental approach: Test layout with finger elements
wn,min = 5µm to wn,max = 50 µm3 identical sections
Evaluation of optimum anilox roll 3 band sections with differentdip volumes (in cm³/m²)
Double printing with intermediatedrying
Characterization of finger width wf,finger height hf and lateral resistance RL
Flexo printed contact finger with nominal width wn = 10 µm
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Experimental ApproachSimulation of Solar Cell Results
Experimental approach: Test layout with finger elements wn,min = 5µm to wn,max = 50 µm
3 identical sections
Evaluation of optimum anilox roll 3 band sections with differentdip volumes (in cm³/m²)
Double printing with intermediate drying
Characterization of finger width wf,finger height hf and lateral resistance RL
Calculation of rs,f and FF according to [4] and [5]
[4] T. Fellmeth et al., IEEE J-PV 4 (2014)[5] A. Mette, Dissertation 2007
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Experimental ApproachSimulation of Solar Cell Results
Experimental approach: Test layout with finger elements wn,min = 5µm to wn,max = 50 µm
3 identical sections
Evaluation of optimum anilox roll 3 band sections with differentdip volumes (in cm³/m²)
Double printing with intermediate drying
Characterization of finger width wf,finger height hf and lateral resistance RL
Calculation of rs,f and FF according to [4] and [5]
Simulation of flexo printed multi busbar solar cells
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Results and DiscussionFinger widths (double printing + intermediate drying)
Experimental Results: wf mainly depending on printing
pressure, dip volume (anilox roll) and nominal width wn
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Results and DiscussionFinger widths (double printing + intermediate drying)
Experimental Results: Finger widths down to
wf,min = 33 µm could be achieved
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Results and DiscussionFinger height
Experimental Results: Finger widths down to
wf,min = 33 µm could be achieved
hf between 5 and 8 µm f
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Results and DiscussionLateral conducitivity of fingers
Experimental Results: Finger widths down to
wf,min = 33 µm could be achieved
hf between 5 and 8 µm
Finger resistance per unit lengthRL,FX 500 -1500 /m(Screen printed fingers:RL,SP 40 – 70 /m)
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Results and DiscussionContribution to series resistance / fill factor loss
No. of Busbars
Finger res.[/m]
# Fingers Contribution of fingers to Rs
[cm²]
Fill factorloss [%]
5 1000 200 0.629 3.5810 1000 130 0.240 1.3715 1000 115 0.120 0.6820 1000 110 0.070 0.40
Assumptions: Multi-busbar solar cell with 5, 10, 15 and 20 copper busbar wires
Uniform fingers on the whole cell
Contact finger width wf = 40 µm
Number of contact fingers has been optimized individually
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Results and DiscussionSimulation of Solar Cell Results
Assumptions: Cz-Si, RSH = 75 /sq, B = 2 cm Al BSF rear side Finger width wf = 40 µm Contact Resistance c = 3.5 mcm² Specific Resistance Copper
BB wires BB = 1.68 µcm Diameter BB wires dBB = 200 µm
Varied parameters: Lateral finger resistance RL Number of contact fingers
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Results and DiscussionSimulation of Solar Cell Results
Assumptions: Cz-Si, RSH = 75 /sq, B = 2 cm Al BSF rear side Finger width wf = 40 µm Contact Resistance c = 3.5 mcm² Specific Resistance Copper
BB wires BB = 1.68 µcm Diameter BB wires dBB = 200 µm
Varied parameters: Lateral finger resistance RL Number of contact fingersFlexo printed
contact fingers
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Flexographic Printing for Multi-Busbar Solar CellsSummary + Outlook
Experimental results:
Flexo double printed contact fingers down to 33 µm demonstrated
Lateral resistance RL 500 - 1500 /m
Contribution to rs / FF and Simulation of solar cell results underline the potential of flexographic printing for multi busbar solar cells
Challenges and further research:
Optimize process stability, reduce tolerances of materials and process
Verify the results of the fundamental research by realizing flexo printedmulti busbar cells
Profound CoO-Calculation
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Thank you for your attention!
… and all Co-workers at PVTEC … as well as our industry partners who supported this work: