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Thesis defence 2011-03-04

This is the presentation I used during my Ph.D. thesis defence on March 4th 2011. Comments are welcome!
by

Per-Oskar Westin

on 12 June 2012

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Transcript of Thesis defence 2011-03-04

Laser Patterning and Stability
in CIGS Thin Film Photovoltaics Copper - Indium - Gallium - (di)Selenide u n a e 2 1-x x Light
Amplification Stimulated
Emission
Radiation By Means of Beams Per-Oskar Westin Thesis defence 2011-03-04
Å4001, Ångströmlaboratoriet Active cell width
(90-95%) Total cell width Interconnect zone
width
(5-10%
"dead" area) "P1"
"P2"
"P3" Back contact: Mo Absorber: CIGS P1 P2 P3 State of the art patterning: P1 State of the art patterning : P2 State of the art patterning : P3 Reminder: Monolithic interconnection - P3 isolation using picosecond laser
- Indirect induced ablation of ZnO:Al
- No significant change in CIGS composition
- Very shallow depth of ablation
- Working devices with FF as good as references - P2 by Transformation of CIGS
- Process performed before
ZnO:Al layer deposition
- Partial evaporation leads to
Cu-rich CIGS/Cu Se phase
- Electrical conductivity across the
phase connects Mo to ZnO:Al Only a fraction...
... and yet so much ( Buffer: CdS Barrier: i-ZnO Front contact: ZnO:Al 1 Cell Thank you for your attention! Basic concepts Stability Outlook Laser patterning Isolation of adjacent back contacts
Cell size definition
Direct laser ablation of Mo layer Via opening for series connection
Mechanical removal of CIGS/CdS using metal stylus Isolation of adjacent front contacts
Mechanical removal of all semiconductors
using a metal stylus P1:
Isolation P2:
Connection P3:
Isolation Advantages of laser patterning Narrower and more controlled lines
Compatible with high speed
No mechanical stress on substrate
Less tool maintenance and downtime


Interconnect area
reduced to 3% Note: The P2-P3 spacing is not representative for an industrial process Experimental work P2: Transformed CIGS - P2 by Transformation of CIGS
- Process performed before
ZnO:Al layer deposition
- Partial evaporation leads to
Cu-rich CIGS/Cu Se phase
- Electrical conductivity across the
phase connects Mo to ZnO:Al P2: Transformed CIGS - Can we exploit the transparency of the
ZnO:Al layer to achieve a post-window
patterning process? P2: Laser "micro-welding" - Can we exploit the transparency of the
ZnO:Al layer to achieve a post-window
patterning process?
- YES! "Laser micro-welding"

- Working modules made reproducibly
- Favorable with low pulse energies
and highly overlapping pulses Experimental work Thin films are sensitive
protect from humidity
protect from mechanical damage Top glass
Encapsulant
Edge Seal
Substrate glass IV-curve Band diagram Si wafers/Thin films Monolithic
interconnection The laser cavity and beam formation - P3 isolation using picosecond laser
- Direct ablation of ZnO/CIGS
- Difficult to control at CIGS/Mo interface
- Cracking of Mo, edge effects
- Working devices with some reduced FF
- Best device: 10.0% Efficiency, 60.1% FF
(Ref: 10.6% 65.5%) PAPER I Composition Topography (2 hrs sunlight > 1 year consumption) State of the art patterning
- Problems with chipping and process control for mechanical patterning - P3 isolation using picosecond laser
- Indirect induced ablation of ZnO
- CIGS surface not disturbed (composition)
- No edge effects, no cracking
- Modules comparable to references
- Best module 11.0% Efficiency, 66.9% FF
(Ref: 10.5 %, 65.5%) PAPER I Cu rich residual phase PAPER III Good module performance PAPER VII The dominating phase
remains chalcopyrite (CIGS or Cu Se) x Highly overlapping, low energy pulses result in more Cu rich residual phase PAPER V PAPER VI Low energy pulses result in a heterogeneous compound where segregated Cu Se was found Results improved with defocused laser beam Proof of concept study
Successful patterning on various CIGS thicknesses and compositions
Scale-up to 30x30 cm module Encapsulation + edge seal necessary (PAPER II) Microweld P2 stability issues
(PAPER VI) A Photovoltaic "Module" - a series of interconnected cells The Sun LASER Patterning influences performance! P3: Direct ablation - P3 isolation using picosecond laser
- Direct ablation of ZnO/CIGS
- Difficult to control at CIGS/Mo interface
- Cracking of Mo, edge effects
- Working devices with some reduced FF P3: Indirect induced ablation (Sun)light Laser light High energy pulses } Pulse duration
10 s
10 s } } Pulse duration
Pulse repetition rate
1-100 kHz -9 -12 Advantages P2 is performed after active layers have been deposited
- Control of film interfaces
- Continuous vacuum process possible P3 laser scribing
-Picosecond laser P2 laser scribing
-Nanosecond laser Advantages of laser micro-welding Advantages for cells Processing advantages All-vacuum processing
- Less pumping times Combined tool
- Less time for patterning
- Smaller footprint Coating processes uninterrupted by patterning More studies to improve process control
Extended stability studies
Modelling of laser process to aid process development ZnO window CIGS absorber Mo contact Mo contact ~0.5µm ZnO window ~1µm CIGS absorber 1-2 µm Cell 1 Cell 2 CIGS
dep. Buffer
dep. P2
patt. ZnO
dep. P3
patt. CIGS
dep. Buffer
dep. P2
patt. ZnO
dep. P3
patt. State of the art CIGS
dep. Buffer
dep. P2/P3
patt. ZnO
dep. P2: Laser "micro-welding" Picosecond pulses Nanosecond pulses 10-100 picosecond pulses
Absorption depth ~10 nm
Heat conduction ~10 nm 10-50 nanosecond pulses
Absorption depth ~10 nm
Heat conduction ~1 µm P1 P3 P2 Single wavelength
High intensity
Low divergence Nanoseconds
Picoseconds Additional peaks
1 - Se
2 - In Se
3 - Cu O
4 - Cu In
5 - Ga O 4 3 4 3 2 2 0.9 0.1 2 3 Challenges Mo damage Glass damage x x Damp heat test: 85 C / 85% RH o Dry heat test: 85 C o Performance Composition Topography Performance Sharp edge Speed reduced to 1/10 26 J/cm X 43 J/cm 56 J/cm 2 2 2
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