Atmospheric plasma surface modification for continuous processing of solar cells
Aluminum Foil Cleaning Process Caustic Chemical (Wet) Cleaning APT (Dry) Cleaning
Active Cleaning Agent(s) Water-base Sulphuric Acid Ion/Electron/Photon Bombardment
Alkaline Solutions Inert + Non-hazardous Reactive Gas
Alcohol Solutions
Dissolved within Caustic Chemical Rolling Oils
Oxides
Water-Soluble Derivatives
Entrained in Process Exhaust Volatilized hydrocarbon particles
Aluminum oxide particles
Water-Soluble Aluminum Derivatives
Emissions Water Laden w/ Chemical Wastes 15 ppm Ozone
Inert gas (98%)
Reactive gas (90%)
<10 ppm CO2
<10 ppm Water Vapor
Volatized surface particulates
Recurring Process Costs Fresh Water, Additional Chemicals Process Gases
Handling, Disposal Costs
Table 1. Wet vs. dry solar cell base material surface cleaning.
72 dynes/cm. Polyimide film was also
Solar Material APT Surface Treatment Purpose Treatment Protocol
treated using a reactive silane-based wet
chemical primer treatment. Both surface
EVA top-coated PVC Improve adhesion of solvent Argon/O2 plasma,
treated films were laminated to aluminum
adhesive to PVC 343W/ft
2
/in
foil and then subjected to a foil strain Cadmium Telluride Improve adhesion of cadmium Argon/O2 plasma,
gauge test. The peel force results in Table 3
telluride to glass 145W/ft
2
/in
indicate a 22% improvement in bonding
Unannealed Hydro Foil Clean unannealed foil surface Helium/O2 plasma,
strength using APT surface modification
40W/ft
2
/in
vs. chemical primer pre-treatment.
Thin film solar cells Clean foil of organic particles Helium/O2 plasma,
30W/ft
2
/in
conclusion
Solar power is a technology of the future.
Aluminum foil Clean foil for lamination of Helium/O2 plasma,
Successful commercialization of low
water-based coatings 30W/ft
2
/in
cost, high efficiency fabrications is highly
Silicon wafer (roll form) Improve wettability for Helium/O2 plasma,
dependent upon fabrication methods that photovoltaic modules 54.5W/ft
2
/in
employ continuous processing techniques.
Polyimide film Improve surface wettability Argon/O2 plasma,
One major issue encountered in solar
for metal adhesion 20W/ft
2
/in
cell construction is the adhesion of thin
film solar cells on polyimide substrates.
Table 2. Base material pre-treatment protocols.
We evaluated the adhesion promotion
potential of variable chemistry atmospheric
plasma surface modification against wet
Polyimide Strain Gauge Film Metal Adhesion Results
primer chemistry on a polyimide-based
Sample Peel Force
substrate to determine their comparative
bonding strengths to aluminum foil. It
Cadmium Telluride Improve adhesion of cadmium telluride to glass
was apparent that APT is a viable continu-
Unannealed Hydro Foil Clean unannealed foil surface
ous and environmentally friendly process
alternative to batch plasma and surfactant-
Thin film solar cells Clean foil of organic particles
based surface modification protocols. Aluminum foil Clean foil for lamination of water-based coatings

Silicon wafer (roll form) Improve wettability for photovoltaic modules
references
1. S. Schaefer, H. Lautenschlager, M. Juch,
Polyimide film Improve surface wettability for metal adhesion
O. Siniaguine, R. Lüdemann, “An
Table 3. Peel-adhesion comparison of APT vs. chemical primer.
continued on page 25
10 – Global Solar Technology – September/October 2008 www.globalsolartechnology.com
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