Thermoplastic Polyimide Direct Bonding Solar Cells
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Solution Overview
Problem
Current solar panel designs face issues with weight, thermal expansion mismatch, and adhesive degradation, which affect the efficiency and longevity of solar arrays, particularly due to the use of RTV adhesives with high thermal expansion coefficients.
Innovation Solution
A method involving the direct bonding of thermoplastic polyimide to solar cells using specific diamine and dianhydride monomers, which matches the thermal expansion coefficient of the solar cells, eliminating the need for RTV adhesives and reducing weight and thermal stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If RTV adhesive is used to bond solar cells to substrate, then bonding strength is achieved, but thermal expansion mismatch causes stress and degradation
Solution Approach 1:
The patent changes the material parameters by selecting a polyimide adhesive with a coefficient of thermal expansion (5-20 ppm/°C) that closely matches the solar cell (2-10 ppm/°C), fundamentally altering the thermal expansion characteristics of the bonding system to eliminate stress during thermal cycling
Solution Approach 2:
The patent employs a composite material approach by using polyimide that combines adhesive functionality with thermal expansion matching properties, creating a multi-functional material that simultaneously bonds solar cells and accommodates thermal stresses
2Strength
If multiple layers (solar cell, adhesive, insulative facesheet) are bonded together, then structural integrity is achieved, but weight increases
Solution Approach 1:
The patent merges multiple functions into fewer layers by using polyimide that simultaneously provides adhesive bonding and thermal expansion matching, eliminating the need for separate adhesive and insulative layers while maintaining structural integrity
Solution Approach 2:
The polyimide material serves multiple functions: it acts as the bonding adhesive, provides thermal expansion matching, and offers electrical insulation, consolidating what would traditionally require separate components into a single multi-functional material
3Strength
If high thermal expansion coefficient adhesive is used, then bonding is achieved, but thermal stress during temperature cycles causes degradation
Solution Approach 1:
The patent fundamentally changes the thermal expansion parameter of the adhesive from high (100-200 ppm/°C for RTV) to low and matched (5-20 ppm/°C for polyimide), enabling the bond to withstand repeated thermal cycling without stress-induced degradation
Solution Approach 2:
The polyimide adhesive provides beforehand cushioning by accommodating thermal expansion differences before they can cause stress, effectively pre-compen sating for thermal cycling effects that would otherwise degrade the bond over time
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
This approach reduces the overall weight and thermal stresses of solar arrays, increases their lifespan, and enhances thermal and power efficiency by aligning the thermal expansion coefficients of adjacent layers, thereby improving their performance and reducing manufacturing costs.
Implementation Method 1
heating a thermoplastic polyimide to at least its reflow temperature
Implementation Method 2
flowing the thermoplastic polyimide onto the back side of the solar cell while heated to at least its reflow temperature
Implementation Method 3
cooling the thermoplastic polyimide to a temperature below its reflow temperature to bond the thermoplastic polyimide directly to the solar cell
Implementation Method 4
The thermoplastic polyimide has a coefficient of thermal expansion of ± 1%-5% of a coefficient of thermal expansion of the solar cell
Data Source
Figure 1~2
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AI summary
A method of constructing a solar cell panel is disclosed that includes providing a solar cell that has a front side and a back side, where the front side faces the sun during normal operation, heating a thermoplastic polyimide to at least its reflow temperature, flowing the thermoplastic polyimide onto the back side of the solar cell while heated to at least its reflow temperature, and cooling the thermoplastic polyimide to a temperature below its reflow temperature to bond the thermoplastic polyimide directly to the solar cell. The direct bonding of the thermoplastic polyimide to the solar cell is accomplished without an adhesive such as RTV adhesives. The method may also include bonding a substrate directly to the thermoplastic polyimide opposite the solar cell.