Jörg Schwartz, firstname.lastname@example.org
GROßRÖHRSDORF, Germany – In-line metrology systems developed by industrial vision specialist Basler Vision
Technologies have been integrated into the production line of solar module manufacturer
Sunfilm AG at its Großröhrsdorf plant near Dresden. The company is the
first manufacturer to introduce large-scale production of silicon-based tandem junction
thin-film modules, at a plant that went into production in April 2009 and uses Applied
Sunfilm’s production facility manufactures tandem junction
thin-film solar modules in Großröhrsdorf, Germany. The plasma-enhanced
chemical vapor deposition system is important for depositing critical light-absorbing
silicon layers on 5.7-m2 glass substrates, with the quality of the coating being
checked by optical metrology systems. Courtesy of Business Wire.
Thin-film solar modules use about 2 percent of the amount of silicon
per watt of electricity produced compared with traditional solar cells fabricated
using crystalline silicon wafers. Even more importantly, tandem junction cells’
photovoltaic devices offer higher efficiency by better utilizing the solar spectrum.
They use more than one semiconductor material, each with a different bandgap –
i.e., absorption peak – which means that larger parts of the solar spectrum
are “harvested” or absorbed and converted into electrical energy. Sunfilm
makes cells with two materials, a combination of amorphous and microcrystalline
silicon. This combination offers more than 8 percent efficiency with a prospect
of 10 to 12 percent in the longer term; solar cells using a single layer of amorphous
silicon convert only about 6 percent of sunlight.
Making these cells requires several process steps because the
production involves deposition of several thin layers on a transparent conductive
oxide (TCO)-coated float glass substrate. Key elements are the absorber layers –
i.e., amorphous and microcrystalline silicon – but equally important is the
back contact, consisting of another conductive oxide and several metal layers, as
well as protective and encapsulation/lamination layers. Accurate process handling
is therefore absolutely essential, particularly for large sizes involved. Up to
5.7-m2 substrates are processed in the factory, so metrology systems are important
to support the “latest state-of-the-art process control,” as Dr. Wilhelm
Stein, Sunfilm’s chief engineer noted.
Basler’s solution is based on the company’s experience
in LCD inspection, built over the past 10 years and now adapted and optimized for
thin-film applications. It is used to perform three different jobs in the solar
cell production line. First, the glass is inspected (TCO-coated or -uncoated), and
the cleaning process is checked. At this stage, edge defects are of particular importance
because they can lead to glass breakage and significant production downtime.
Pictured is Basler’s imaging system, first developed for liquid
crystal display manufacturing and now integrated into a solar cell production line
that can process 5.7-m2 glass substrates. The system helps improve efficiency and
reduces the cost of solar module manufacturing.
Once the glass passes inspection, a second system checks the semiconductor
coatings applied via plasma-enhanced chemical vapor deposition (PECVD). Here, pinholes
are the biggest issue, as they will cause short circuits that reduce the efficiency
of the photoactive layers. The detection system not only counts the number but also
provides the distribution of the pinholes.
Finally, after the lamination process, the end product is checked
for bubbles, scratches and delamination on the peripheral and photoactive areas.
Lamination bubbles on the edge of solar modules can lead to penetration of moisture,
degrading the lifetime of the product.
The metrology system has been fully integrated with the factory
automation system via the SECS/GEM protocol. The semiconductor industry uses this
interface for equipment-to-host communications. In an automated fab, it can start
and stop equipment processing, collect measurements, change variables or select
recipes for products – and now it has the vision to support greener energy