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Solar Awards Thin Film Innovation Award Final DR 2/9/09 15:38 Page 28
SOLAR AWARDS
NF3-based cleaning processes alone Research with over 350 MWp of installed thin as possible while keeping the
adds significantly to the carbon footprint production capacity, the TCO 1200 efficiency high. In addition, amorphous
payback time, or time the solar module systems have become the de facto silicon single junction cells have an
needs to function and displace carbon- industry standard for the production of enhanced susceptibility to Staebler-
based fuels in order to have a net positive thin film silicon solar modules. Wronski degradation, so efficient light
impact. Typically 1 tonne of NF3 is management allows a reduction in layer
required for chamber cleaning for each TCO films have been used within thin film thickness, fundamental for high
MWp nameplate capacity solar fab. So PV panels since the beginning of the performance in these material systems.
for example, these modules, when technology. The TCO film needs to: allow The output current of an Oerlikon Solar
deployed in Germany, add approximately full spectrum light onto the panel for TCO film is significantly higher than a high
Issue IV 2009
2 years to the carbon payback time. generation of energy by the PV absorber, quality commercial APCVD film,
Because the GWP of F2 is zero, the act as a current collector and act as a accounting for an additional 0.5%
carbon payback time due to F2-based light scattering and trapping layer which improvement in stabilized efficiency. The
cleaning is nearly zero. forces key wavelengths to traverse the PV TCO 1200 LPCVD manufacturing system
absorber stack for multiple reflections, allows in a single layer to optimize a
Reduced cost per watt: increasing the chance for the light to tandem absorber stack with very high
On-site generated F2 reduces the cost create electricity. haze light scattering, very low sheet
-pv-management.com per watt through reduced mass resistance and excellent
consumption, faster clean times, and The standard technology for deposition of transmission characteristics. Also, the low
.solar
reduced capital expenditure, with savings TCO films has been sputtering. temperature nature of the deposition
www
of 3 to 5 ¢/W for a typical thin-film PV fab. Unfortunately the sputtering process allows this same TCO layer to be used
Because only the fluorine atoms are allows only a small window of process successfully for the TCO back contact,
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responsible for chamber cleaning, 20% adjustment and no optimization of again increasing light trapping within the
less F2 is required vs NF3; for less material composition or light scattering. cell. Until today over 900’000 panels have
efficient activation processes such as in- Another popular approach to TCO been produced using the TCO 1200
situ activation, this savings can be fabrication, especially by glass systems from Oerlikon Solar for front and
significantly greater. Chamber cleaning manufacturers, is Atmospheric Pressure back contacts. The additional 0.5%
with NF3 can take from 15 to 25% of the CVD (APCVD). APCVD techniques efficiency gained translates into higher
total amount of time a CVD tool is in typically require very high deposition power per module and also in a
operation. Cleaning with F2 can reduce temperatures, >500° C, and so forces the significant economic benefit: e.g. 100 Wp
chamber cleaning times by a factor of 2 films to be applied to the glass directly modules are becoming 105 Wp modules
to 4, and therefore greatly increase the without any PV absorber films present. which means to the solar farm developer
throughput on a critical step of thin-film This is possible only for the first film on a direct module savings of 5%. In a 30
PV production. And because much less glass at the beginning of module MWp solar farm with 300’000 modules
energy is required to activate F2 vs NF3, manufacture, however, the back contact this accounts to saving 15’000 installed
smaller, less expensive equipment can be TCO film cannot be deposited by APCVD. panels or about $3 million.
used for activating F2. The TCO 1200 LPCVD (Low Pressure
Chemical Vapor Deposition) reactor has
several new hardware and chemistry
Oerlikon Solar Ltd
innovations, allowing a fast and highly
Robert Bürkle GmbH
uniform IR camera controlled heating, a Multi-Opening Lamination Line
TCO 1200 System low temperature process (<200° C) and Ypsator
controllable conductivity and crystal
The Oerlikon Solar TCO 1200 is a fully morphology through adjustable doping The Ypsator is a Multi-Opening
automated high volume system for the gas delivery. These features allow the film Lamination Line for the production of
deposition of a novel and adjustable to be adjusted to optimize panel power glass-glass modules (thin-film modules)
Transparent Conductive Oxide (TCO) film. output. onto several openings from Bürkle, the
The TCO 1200 process technology allows pioneer of the multi-opening technology.
adjustment of film morphology and In order to develop the next generation The modules are laminated in a 3-step
conductivity to match ideal parameters for thin film silicon PV cells, light trapping by process. In the first step pre-lamination
the PV absorber stack while utilizing an advanced TCO is essential. The new via vacuum is made, in the second step
innovative ZnOx film composition with LPCVD process from Oerlikon Solar has the final lamination is done via hydraulics,
superior light trapping versus standard demonstrated higher light trapping in the 3rd step the module is cooled
SnOx films. As Oerlikon Solar is the abilities. This is especially important for down in the cooling unit.The final
number one supplier of end-to-end micromorph solar cells where the lamination in the second step, the second
production lines according to VLSI absorber layers are engineered to be as press, the modules are laminated with
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