Ag_LIP_GSF_0909_E

PV T h l Technology F Forum 2009 – K th i Butz Kathrin B t
PHOTOVOLTAIC Perfection
Production and Process Flow
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Agenda
Electrolytic Ag LIP deposition on a screen printed layer y g p p y Design of the front side structure – conventional screen printing technology – Stateof-the-art Design of the front side structure by an optimized screen printing and Ag LIP Design of the front side structure by LTP and Ag LIP Increase of grid conductivity by pure galvanic Ag I f id d ti it b l i A Efficiency increase of the PV cell
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Light induced silver plating Ag LIP
Placement in Solar Cell Production Line
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Horizontal Wet Process Equipment
Light Induced Silver Plating Ag LIP
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Conventional screen print technology
Low conductivity and homogeneity resulting from using the screen printing paste only Difficulty: width finger print resulting in shading Conventional screen printing is not adequate for the LIP
screen printed contact 15 μm 15 μm 120 μm 120 μm
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Schmid-Solution
Design of the front side structure by an optimized screen printing and Ag LIP g y p p g g
- The generation of an optimized finger width of approx. 70 μm – 80 μm reduces shading on the front side - The serial resistance is reduced by a galvanic deposition of Ag on the screen print - The so called healing effect results from applying Ag on the screen printing
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Target – reducing of the serial resistance
Compared to a conventional printing, the optimized screen printing reduces the shading effect up to 33%. Shading is linear to efficiency.
- small width - high aspect ratio (height / width) - low specific line resistance screen printed contact
Shading reduction Shading reduction Screen print with LIP 85-95 μm Optimized screen print 70-80 μm
15 μm 120 μm
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Schmid-Solution
Front side structure by LTP and Ag LIP y g
LTP conductivity layers with finger width of approx. 40 μm – 60 μm are generated contactless resulting in higher shading reduction as is achieved by the optimized conventional screen print. The serial resistance is reduced by galvanic deposition of Ag on top of the Ag LTP seed layer increase of the cell capacity
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Schmid-Solution
LTP 40 – 60 μm; LTP + LIP ca. 50 – 70 μm LTP reduces the shading effect up to 58%. Shading is linear to efficiency.
- small width - high aspect ratio (height / width) - low specific line resistance screen printed contact i t d t t
Optimized screen print with LIP 85-95μm Screen print 70-80 μm
15 μm
Shading reduction Additional shading reduction LTP 40-60μm Shading reduction Additional shading reduction
Conventional printed finger width 120 μm
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Path to Improved Cell Efficiency
Reduced width, starting paste line + LIP Ag
= Smaller finished line width to standard full-paste process = Si il I values Similar Isc l
Higher conductivity, plated Ag deposit, driving higher cell efficiency
- Lower Rbb and Rs - Higher Fill Factor (FF) - Improved Cell Efficiency = + 0.3 to 0.4% (over standard full paste process)

Path to Improved Cell Efficiency
The reducing of the finger width resulting in an increase of efficiency.

Schmid-Solution
Increase of the electrical grid conductivity by using pure galvanic Ag
Electrolytically deposited Ag has the least metallical resistance and shows a good reflection behavior in the module
LIP Ag layer over Ag screen printed seed layer
REM- profile view of screen print contact (blown layer = lower conductivity) with Ag reinforcement through LIP (compact + homogeneous layer = high conductivity)
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Solar cells with optimised front side cell structure
Screen printed Ag seed Layer 70 μm wide id
Ag LIP plated finger 95 μm wide id

Cell conditons for cell efficiency increase by Ag LIP processing
Narrow lines are creating less shading – approximate 70-80 μm wide after screen printing Optimized number of lines on front grid Closed grid design – 1 external line around the cell edges linked to fingers Printed lines profile – free of smear, breaks and waviness Good ohmic contact by compatible Ag pastes and optimized firing conditions Rear Al paste type with good adhesion and compatible with Ag LIP process Non scratching by handling in ARC Pinhole f Pi h l free ARC – no SiN porosity SiNx i Good edge isolation and if possible coverage by ARC to prevent edge plating Chemical d i l ti Ch i l edge isolation on rear side id

Solar cells with optimised front side cell structure
Cell with circumferential external line to prevent local high current density
Cell without circumferential externel line

Schmid-Solution
Improvement of the PV cell efficiency p y
A optimized grid with reduced finger width and a galvanic Ag deposition increases the cell capacity up to 0,3 % - 0,4 % LTP Laser Transfer Print and galvanically deposited Ag LIP grids will result in a continue rising of cell capacity in future.
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Process results
LIP Silver Processing Reduces Final Cell Efficiency Variation
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Schematical process flow
contact roll cell conveyor DC
Ag anode g a ode Light source
Soluble Ag anodes Ti contact rolls DC rectifiers, sectional controlled LED sources – Light intensity adjustable alternative Fluorescent light sources Light sources – wave length adapted to electrolyte light transmission capability g g y g y Sunny side down
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Commercially available Light-Induced-Plating-Machine

Commercially available Light-Induced-Plating-Machine
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