Solar Cell Module Resin Bonding Warping Stress
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Solution Overview
Problem
Solar cell modules face issues with warping stress, cell cracks, and electrode peeling due to differences in linear expansion coefficients between wiring members and solar cells, particularly exacerbated by thinner solar cells and thicker wiring members, which affect production yield and reliability.
Innovation Solution
The use of a resin as an adhesion material for bonding collecting electrodes and electric conductors at lower temperatures, which covers the side surfaces of the electrodes and may contain fine particles, to reduce warping stress and enhance adhesion, thereby preventing cell cracks and electrode peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If the thickness of the solar cell is reduced to lower production cost, then production cost is reduced, but warping stress increases causing cell cracks and electrode peeling
Solution Approach 1:
The patent introduces a resin layer as an intermediary substance between the solar cell and the wiring member. This resin layer absorbs and distributes the warping stress generated during thermal expansion and contraction, preventing direct stress transmission to the thin solar cell that would cause cracking or electrode peeling, thereby enabling the use of thinner, more cost-effective solar cells without compromising reliability
2Reliability
If the thickness of the wiring member is increased to reduce serial resistance, then electrical conductivity is improved, but warping stress increases causing solar cell warpage
Solution Approach 1:
The resin layer serves as a stress-absorbing intermediary between the thick wiring member and the solar cell. It distributes the mechanical stress from the rigid wiring member across a larger area, preventing localized warping of the solar cell while maintaining the electrical conductivity benefits of the thicker wiring member
Solution Approach 2:
The patent changes the physical and chemical parameters of the bonding interface by using a resin material with specific viscoelastic properties. The resin's ability to deform and relax under stress, combined with its adhesion characteristics, allows it to accommodate the dimensional mismatch between the wiring member and solar cell, reducing warpage while preserving electrical performance
3Strength
If soldering temperature is increased to improve bonding strength with lead-free solder, then adhesion is improved, but warping stress increases causing cell cracks
Solution Approach 1:
The resin layer acts as a thermal buffer and mechanical intermediary during the soldering process. It absorbs and distributes the thermal stress generated during high-temperature lead-free soldering, preventing direct transmission of thermal shock to the solar cell that would cause cracking, while still allowing adequate bonding strength to be achieved
Solution Approach 2:
The resin layer is positioned in advance between the solar cell and wiring member to provide preemptive protection against thermal and mechanical stress. This pre-positioned cushioning layer is designed to accommodate the expected thermal expansion and contraction during the soldering process, preventing cell cracks before they occur
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 effectively suppresses warping stress, cell cracks, and electrode peeling, while also preventing water penetration and improving the adhesion and long-term reliability of the solar cell module by embedding electrodes into a soft electric conductor and using a low-temperature bonding process.
Implementation Method 1
a resin adhesive material is used as adhesive material of the wiring member and the collecting electrode
Implementation Method 2
A solar cell is expected as a new energy source because it can directly convert light from the sun, which is clean and inexhaustible energy source, into electricity
Implementation Method 3
linear expansion coefficients of the wiring member 141 being a copper foil, for example, and the solar cell 101 formed of a crystal silicon substrate are 17.8 ppm/°C and 4.2 ppm/°C, respectively, and differ by a factor of more than four. Accordingly, the degrees of expansion and shrinkage due to heating and cooling at a time of soldering to connect the wiring member 141 to the bus bar electrode 121 formed on the solar cell 101 differ among these materials
Data Source
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AI summary
A solar cell module includes a plurality of solar cells 1 connected to each other in a way that bus bar electrode 21 formed on surfaces of adjacent solar cells 1 are connected to each other with wiring members 41,42. The bus bar electrode 21 is embedded in the wiring member 41, and the solar cell 1 and the wiring member 41 are bonded together with a resin.