UV-Stable Polyester Film for Photovoltaic Encapsulation
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Solution Overview
Problem
Polyester films used in photovoltaic cells, particularly thin-film CIGS PV cells, face challenges with UV-stability, light transmittance, adhesion to encapsulant materials, and thermal dimensional stability, which affect the efficiency and longevity of the cells.
Innovation Solution
A composite film comprising a heat-stabilized, biaxially oriented polyester substrate with a UV-absorber and a thin ethylene acrylic acid copolymer coating layer, providing improved UV-stability, light transmittance, adhesion, and dimensional stability without the need for additional surface treatments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a transparent polymeric layer is used in PV cells to protect the photo-active layer, then adhesion to encapsulant material is improved, but UV-stability deteriorates causing yellowing and hazing
Solution Approach 1:
The patent uses a composite structure consisting of a polyester substrate layer and a separate polymeric coating layer. The polyester substrate provides UV-stability and mechanical strength, while the polymeric coating provides adhesion to the encapsulant material. This composite approach allows each layer to perform its specific function without compromising the other, resolving the contradiction between adhesion and UV-stability.
Solution Approach 2:
The protective layer is segmented into two distinct functional layers: a polyester substrate that provides UV-protection and mechanical integrity, and a polymeric coating that provides adhesion to the encapsulant. This segmentation allows each layer to be optimized for its specific function, with the polyester handling UV-stability and the coating handling adhesion, thereby resolving the technical contradiction.
2Illumination intensity
If polymeric materials are used for transparent layers in PV cells, then light transmittance is improved, but thermal dimensional stability deteriorates causing wrinkling and movement
Solution Approach 1:
The patent employs a composite structure where a heat-stabilized polyester substrate provides thermal dimensional stability, while a polymeric coating layer provides light transmittance and adhesion. The polyester substrate acts as a dimensionally stable base that prevents wrinkling and movement during manufacturing, while the polymeric coating maintains optical properties. This composite approach resolves the contradiction between light transmittance and thermal stability.
Solution Approach 2:
The polyester substrate is specifically heat-stabilized through controlled heat treatment processes that adjust its crystallinity and dimensional stability parameters. This parameter change allows the polyester to maintain its shape and size during PV cell manufacturing at elevated temperatures, preventing the wrinkling and movement that would otherwise occur with conventional polymeric materials.
3Strength
If additional surface treatment is applied to improve adhesion between protective layer and encapsulant, then adhesion is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The polymeric coating layer is applied to the polyester substrate in advance during the manufacturing process, creating a pre-treated surface that inherently provides good adhesion to the encapsulant. This preliminary action eliminates the need for subsequent adhesion-promoting surface treatments such as corona discharge or plasma treatment, thereby simplifying the manufacturing process while maintaining strong adhesion.
Solution Approach 2:
The polymeric coating layer itself serves the dual function of protecting the polyester substrate and providing adhesion to the encapsulant material. The coating's chemical composition and surface properties are inherently suited for bonding with the encapsulant, eliminating the need for separate adhesion promotion treatments. This self-service approach reduces manufacturing complexity while achieving the desired adhesion.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The composite film achieves high light transmission, enhanced UV-stability, improved adhesion to encapsulant materials, and reduced thermal shrinkage, thereby increasing the efficiency and service life of photovoltaic cells while simplifying manufacturing processes.
Implementation Method 1
a heat-stabilised oriented polyester substrate comprising a UV-absorber in an amount of from about 0.1 to about 10% based on the total weight of the polyester substrate
Implementation Method 2
on one or both surfaces of the substrate a polymeric coating layer, which has a thickness in the range of from about 10 nm to about 200 nm, and which comprises an ethylene acrylic acid (EAA) copolymer
Implementation Method 3
a heat-stabilised oriented polyester substrate
Implementation Method 4
the composite film exhibits a shrinkage at 150°C for 30 minutes of less than 0.1 % in both the longitudinal and transverse dimensions of the film
Data Source
AI summary
A composite film comprising: (i) a heat-stabilised oriented polyester substrate comprising a UV-absorber in an amount of from about 0.1 to about 10% based on the total weight of the polyester substrate, and (ii) on one or both surfaces of the substrate a polymeric coating layer, which has a thickness in the range of from about 10 nm to about 200 nm, and which comprises an ethylene acrylic acid (EAA) copolymer, wherein the composite film exhibits a shrinkage at 150°C for 30 minutes of less than 0.1% in both the longitudinal and transverse dimensions of the film, and use thereof in the manufacture of photo-voltaic cells.