ENLIGHT™ Polyolefin Back Encapsulant Composite Films

Technical Paper
ENLIGHT Polyolefin
Back Encapsulant
Composite Films
Lowering total lifetime
system costs with innovative
polyolefin film solutions
Coextruded Film Technology Offers Solution to
Common Performance Issues
ENLIGHT Polyolefin Back Encapsulant
Composite Films offer significant
processing and performance
advantages and can help lower the
total lifetime system costs of rigid c-Si
photovoltaic modules.
CO-
EXTRUDED
Back Encapsulant Composite Cutaway
Front
Encapsulant
Film
Encapsulant Layer
Bonding Layer
High-Temperature-Resistant Outer Layer
®Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow
The encapsulant film
and backsheet used in
the construction of rigid
crystalline silicon solar
modules are critical components
of a total solar
module system. These
components provide
long-term durability and
efficiency to the module. Encapsulant films are expected to adhere to a
variety of substrates and have chemical and thermal stability, excellent
optics, and ready processability in thermal lamination processes.
Figure 1: ENLIGHT Polyolefin Back Encapsulant Composite Films
ENLIGHT Polyolefin Back Encapsulant Composite Films feature a
three-layer coextruded polyolefin-based (PO) composite containing an
advanced encapsulant layer integrated into a backsheet.
Top Layer
(glass or plastic)
Frame/Junction
Photovoltaic module constructed with ENLIGHT Polyolefin
Back Encapsulant Composite Film
PV Cell
ENLIGHT Polyolefin
Back Encapsulant
Composite Film
The backsheet is used as the outer skin of the solar module to resist
moisture, protect the module from weathering and UV exposure, provide
electrical insulation, and adhere to the chosen encapsulant films. These
characteristics help extend the reliability and service life of the solar module.
Several challenges limit the overall effectiveness of today’s photovoltaic
modules. The module producers and end users may experience
some degree of performance issues due to adhesion failure with the
encapsulant film and/or backsheet. A primary performance challenge
is delamination of backsheets from the encapsulant film, which is
caused by low adhesion between the component layers. Another commonly
encountered problem is delamination within the different layers
of a backsheet. Poor interlayer adhesion can occur within PET-based
backsheets that are produced with adhesive lamination technology,
especially after harsh environmental exposures. These adhesion-related
failures can increase water diffusion into the solar modules and may
lead to poor heat transfer, a well-known limitation to the most commonly
used backsheet films on the market. These factors can ultimately
lead to module loss of durability and efficiency.
Coextrusion Film Technology Offers “2-in-1” Solution
In order to overcome adhesion failures, The Dow Chemical Company is
developing ENLIGHT Polyolefin Back Encapsulant Composite Films as a
“2-in-1” solution – a sophisticated single film structure that can perform
the duties of both the encapsulant and backsheet for rigid c-Si modules.
Dow uses patent-pending technology (Figure 1) to make a three-layer
composite film (encapsu-
lant, bonding, and outer)
that offers significant
processing and performance
advantages and
can help lower the total
lifetime system costs of
photovoltaic modules.
The simplified “2-in-1” structure
of ENLIGHT Polyolefin Back
Encapsulant Films eliminates
delamination, helping to ensure
easy lamination and improved
module performance.
1

Addressing Adhesion Issues
The coextrusion process used to make ENLIGHT Polyolefin Back
Encapsulant Composite Films has distinct advantages over the current
adhesive lamination process. The technology that creates this three-layer
composite allows the bonding layer to wet, interdiffuse, entangle, and
crystallize with the encapsulant and outer layers, resulting in uniform melt
bonding and high bond strength across all areas during film/foil manufacturing.
The bonds between the film layers exhibit lamellar entanglement
with very diffuse interfacial boundaries provided by the highly compatible
polyolefin (PO) bonding layer of the coextruded structure (Figure 2).
The integrity of the bonding layer significantly increases interlayer bond
strength, reducing the potential for interlayer adhesion failures. This
simplified “2-in-1” structure helps overcome delamination that can occur
between separate encapsulant and backsheet layers and eliminates
potential incompatibility between the encapsulant and the backsheet,
helping to ensure easy lamination and improved module performance.
ENLIGHT Polyolefin Back Encapsulant Composite (BEC) Films have
excellent adhesion to different types of front encapsulant, either EVA
or polyolefin. The high adhesion to the front encapsulant is maintained
even after severe thermal treatments (Table 1). Due to the advantages
offered by Dow’s coextruded polyolefin film technology, the excellent
adhesion between the encapsulant layer in ENLIGHT BEC Films and
the high-temperature-resistant polyolefin outer layer was achieved and
maintained even after 4,000 hours of damp heat and 400 thermal cycles.
Figure 2: Lamellar Entanglement of ENLIGHT Polyolefin Back
Encapsulant Composite Films
2
Polyolefin Bonding Layer
Polyolefin Encapsulant Layer
Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow
Ratio should be:
Outer = 40%
Bonding = 10%
Encap = 50%
Table 1: Adhesion properties before and after thermal treatment
Adhesion N/cm
N/cm after
damp heat 1
N/cm after
thermal cycle 2
Interlayer >15 to destruct >15 to destruct >15 to destruct
Front Encapsulant
Layer
1 Temperature: 85°C; Humidity: 85%; 4,000 hrs
2 -40 to 90°C; 400 cycle
>60 to destruct >60 to destruct >60 to destruct
Coextruded Composite Film Structure Offers
Additional Advantages
In addition to solving adhesion issues, the electrical properties of
ENLIGHT BEC Films are advantaged since coextrusion eliminates
voids or bubbles within or in between the backsheet and encapsulant.
Partial discharge can range from the requirement of 1,000 V to >2000 V,
offering module manufacturers the ability to comply with high voltage
requirements. The dielectric strength meets or outperforms some of the
most widely-used incumbent offerings on the market.
ENLIGHT Polyolefin Back Encapsulant Composite Films offer excellent levels
of moisture barrier protection, consistent with the proven performance of
ENLIGHT Polyolefin Encapsulant Films that are used in rigid c-Si modules.
The Water Vapor Transmission Rates of ENLIGHT Polyolefin Films are
significantly lower than EVA films. 1 All components and interlayer bonds
of the composite structure are highly moisture stable, unlike PET-based
backsheets, and all layers have excellent moisture barrier when compared
to typical encapsulant and backsheet materials. 2
Polyolefin Outer Layer
Polyolefin Bonding Layer
Polyolefin Encapsulant Layer
A cross-section micrograph between the polyolefin encapsulant
layer and the polyolefin bonding layer demonstrates the
lamellar entanglement features of ENLIGHT Polyolefin
Back Encapsulant Composite Films.
1 Based on Dow testing when compared to some EVA-based materials. Data available upon request
2 Based on Dow testing when compared to some commonly-used encapsulant and backsheet materials.
Data available upon request.

The composite structure was designed to provide low temperature
toughness down to -40°C. ENLIGHT BEC Films also offer high levels of
protection from UV exposure and long-term heat aging.
Polyolefin-based films possess properties that can help reduce Potential
Induced Degradation (PID). When ENLIGHT Polyolefin Back Encapsulant
Composite Films are used in module designs containing a polyolefinbased
top encapsulant film (such as ENLIGHT Polyolefin Encapsulant
Film), they can help contribute to higher levels of PID resistance.
ENLIGHT BEC Films can be used with different top encapsulant materials
such as EVA or polyolefin. Using both ENLIGHT BEC Film for the
back component as well as ENLIGHT Polyolefin Encapsulant Film for
the top encapsulant can lead to significant processing and performance
improvements and help reduce total lifetime system costs.
“These coextruded polyolefin films offer broader design
flexibility, allowing the materials to be customized to fit exact
module specifications and needs. By combining two separate
components into one, ENLIGHT Polyolefin Back Encapsulant
Composite Films offer excellent module protection due to the
elimination of delamination, improved electrical insulation, and
higher levels of moisture resistance.”
Dr. Burçak Conley, Application Development Specialist, Photovoltaics Business
“With this new development in the product line for ENLIGHT
Polyolefin Films, Dow can leverage our technical knowledge
in coextrusion and apply the proven performance of ENLIGHT
Polyolefin Encapsulant Films into new application areas. The use
of ENLIGHT Polyolefin Back Encapsulant Composite Films helps
reduce materials and inventories, and can result in significantly
increased production efficiencies. The regional availability of all
ENLIGHT Polyolefin Films can also help our customers improve
working capital management. Overall, the use of this innovative
“2-in-1” encapsulant plus backsheet composite can lead to
significant performance and productivity improvements and help
reduce total lifetime system costs for PV modules.”
Friedrich von Rechteren, Global Business Development Manager, Photovoltaics Business
Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow
Dow is dedicated to finding technologies
that harness the power of the sun and
bring energy to use in many different
ways – through solar farms, rigid and
flexible photovoltaic solar modules, and
more. In addition to ENLIGHT Polyolefin
Back Encapsulant Composite Films, Dow
offers proven performance and production
efficiencies to manufacturers of rigid c-Si
modules with its line of ENLIGHT Polyolefin
Encapsulant Films. The Company also
makes ADCOTE Solvent-based Adhesives
and MOR-FREE Solventless Laminating
Adhesives for backsheet products, electronic
materials used to make photoelectric
cells, polyglycol heat transfer fluids, and
DOW POWERHOUSE Solar Shingles for
residential use.
Authors, The Dow Chemical Company, Photovoltaic Business:
• Dr. Burçak Conley, Application Development Specialist
• Dr. Jeff Bonekamp, Product R&D Scientist
• Friedrich von Rechteren, Global Business Development Manager
3

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