Multi-layer PV Backsheet with Integrated Adhesive
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Solution Overview
Problem
Current photovoltaic (PV) module backsheets are expensive, prone to delamination, and difficult to recycle, with existing adhesive layers requiring crosslinking processes that can lead to cell displacement and aesthetical defects, and lack reliable welding options for junction boxes.
Innovation Solution
A cost-effective, recyclable backsheet with integrated adhesive layers comprising a multi-layer structure including a heat-resistant layer with a PolyPropylene (PP) based protective layer, a MAH-grafted PP tie-layer, and functional PolyEthylene (PE) layers, allowing for coextrusion and colamination without crosslinking, enabling excellent adhesion and weldability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If crosslinking processes are used to achieve adhesion, then bonding strength is improved, but cell displacement and aesthetical defects occur
Solution Approach 1:
The patent changes the chemical parameters of the adhesive layer by using thermoplastic polymers with specific melting points and heat of fusion values. The adhesive layer is designed to melt at lamination temperature (around 150°C) and re-solidify upon cooling, creating strong bonds without requiring crosslinking processes. This parameter change eliminates the harmful effects of crosslinking while maintaining bonding strength.
Solution Approach 2:
The patent replaces the chemical crosslinking mechanism with a physical phase change mechanism. Instead of using crosslinking chemistry to create bonds, the adhesive layer utilizes the melting and solidification of thermoplastic polymers. This substitution of the bonding mechanism eliminates the need for crosslinking processes that cause cell displacement and aesthetic defects.
2Reliability
If traditional adhesive layers are used, then adhesion is achieved, but delamination occurs over time
Solution Approach 1:
The patent uses a composite multi-layer structure where the adhesive layer is integrated with the backsheet layers. The adhesive layer comprises thermoplastic polymers (polyethylene, polypropylene) that are chemically compatible with adjacent layers. This composite structure ensures long-term adhesion reliability by preventing delamination through compatible thermal and chemical properties across all interfaces.
Solution Approach 2:
The patent changes the thermal parameters of the adhesive system by selecting thermoplastic polymers with melting points matched to the lamination process temperature. The adhesive layer melts at around 150°C during lamination to ensure complete wetting and bonding, then maintains stability during service. This parameter optimization prevents delamination over the module's service life.
3Adaptability or versatility
If multi-layer backsheets are used to improve functionality, then performance is improved, but manufacturing complexity increases
Solution Approach 1:
The patent merges the adhesive layer and backsheet into a single integrated multi-layer structure. The adhesive layer is not a separate component but is co-extruded or laminated with the backsheet layers during the same manufacturing process. This merging reduces assembly steps and manufacturing complexity while maintaining the functional benefits of multiple layers.
Solution Approach 2:
The multi-layer backsheet structure serves multiple functions simultaneously: the thermoplastic adhesive layer provides adhesion to PV cells and barrier layers, the polypropylene layers provide mechanical strength and UV resistance, and the integrated structure eliminates the need for separate adhesive applications. This multi-functionality reduces overall system complexity.
4Temperature
If heat resistant materials are used for the backsheet, then thermal stability is improved, but adhesion to active material decreases
Solution Approach 1:
The patent applies local quality by having different layers with different thermal properties. The polypropylene layers provide thermal stability and UV resistance where needed, while the thermoplastic adhesive layers (polyethylene, polypropylene) are positioned in direct contact with the active material to provide adhesion. Each layer is optimized for its specific function, resolving the contradiction between thermal stability and adhesion.
Solution Approach 2:
The thermoplastic adhesive layer acts as an intermediary between the heat-resistant polypropylene backsheet layers and the active material. This intermediary layer has thermal properties that allow it to bond to the active material at lamination temperature while being compatible with the adjacent polypropylene layers. The intermediary enables both thermal stability and adhesion to coexist.
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 solution provides reliable adhesion, dimensional stability, and mechanical integrity during PV module production, allowing for efficient encapsulation of thick crystalline PV cells and watertight connections, while eliminating the need for crosslinking and enabling reliable welding of junction boxes.
Implementation Method 1
a backsheet (10) comprising at least a heat resistant layer (12c) reactive and attached by coextrusion to a MAH-grafted PolyPropylene based tie-layer (12b)
Implementation Method 2
The layer of the backsheet (10), either (12b) or (12a) or (13b), facing the active layer (4) has a residual heat of fusion at lamination temperature of less than 30 J/g, preferably less than 5 J/g, preferably is melted
Data Source
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AI summary
The present invention describes a backsheet (10) for electronic devices comprising at least a heat resistant layer (12c) reactive and attached with a PolyOlefine based tie-layer(s) (12b) provided at the side facing the active material (4) to be encapsulated. Optionally further layer(s) (12a) are provided on top of layer (12b), being Flexible PolyPropylene and/or (co-)PE based layer(s). Optionally a last layer (13b) is provided facing the active material (4) based on (co-)PE based tie-layer (13b), such layer providing good adhesion directly on the back-side of the active material (4), or attached barrier layers.