Solar Cell Finger Electrode Layout to Reduce Warpage and Disconnection
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Solution Overview
Problem
Solar cells face issues with warpage and reduced adhesive strength of finger electrodes, leading to disconnection and decreased conversion efficiency due to differences in linear expansion coefficients between the silicon substrate and electrode materials, and the screen printing method's limitations in forming high-aspect-ratio electrodes.
Innovation Solution
The introduction of auxiliary electrodes that connect the longitudinal ends of adjacent finger electrodes to bus bar electrodes, reducing line resistance and enhancing adhesive strength, while maintaining a high fill factor and conversion efficiency by minimizing warpage and peeling failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If finger electrodes are shortened to reduce warpage, then warpage is reduced, but disconnection of finger electrodes between bus bar electrodes occurs and peeling failure rate increases
Solution Approach 1:
An auxiliary electrode is introduced as an intermediary element to connect adjacent finger electrodes at their distal ends. This auxiliary electrode acts as a mediator that bridges the gap between finger electrodes, providing both mechanical support to prevent peeling and electrical continuity to prevent disconnection, while the main finger electrodes can be kept short to reduce warpage.
Solution Approach 2:
The electrical connection path is segmented into multiple sections: the main finger electrode connects to the bus bar electrode, and the auxiliary electrode connects adjacent finger electrodes at their distal ends. This segmentation allows the finger electrodes to be optimized for one function (reducing warpage by being short) while the auxiliary electrodes provide the complementary function (maintaining reliability through additional connection points).
2Strength
If distal portions of finger electrode are enlarged to increase adhesive area, then adhesive strength is increased, but line resistance increases due to local breaks and fill factor is reduced
Solution Approach 1:
The electrode structure is designed with different properties at different locations: the main finger electrodes maintain a narrow width for low line resistance and high fill factor, while the auxiliary electrodes at the distal ends have larger width to provide enhanced adhesive strength and mechanical support. This local differentiation allows each part to be optimized for its specific function without compromising the overall performance.
3Productivity
If screen printing method is used to form electrodes, then ease of manufacture and productivity are improved, but warpage occurs due to difference of linear expansion coefficient and adhesive strength is insufficient
Solution Approach 1:
The electrode system uses a composite structure combining the main finger electrodes (made by screen printing for ease of manufacture) with auxiliary electrodes (added to provide enhanced adhesive properties). This composite approach allows the benefits of screen printing (high productivity, low cost) to be retained while compensating for its weaknesses (warpage, insufficient adhesive strength) through the addition of auxiliary electrodes with optimized properties.
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 solution effectively mitigates warpage, improves adhesive strength, and maintains high conversion efficiency and long-term reliability by ensuring continuous electric conduction even if finger electrodes are broken, with a minimal increase in manufacturing costs.
Implementation Method 1
longitudinal ends of adjacent two or more of the finger electrodes connected to each bus bar electrode are electrically connected together by an auxiliary electrode
Implementation Method 2
warpage occurs due to a difference of linear expansion coefficiency between the Si substrate and the electrode material such as Al or Ag
Data Source
AI summary
Provided is a solar cell that includes: a semiconductor substrate on which at least pn junctions are formed; a multiplicity of finger electrodes that are formed in a comb-like shape on at least one surface of the semiconductor substrate; and a plurality of bus bar electrodes that are arranged so as to be orthogonal to the lengthwise direction of the finger electrodes and are connected with the finger electrodes. This solar cell is configured so that the finger electrodes connected with one of the bus bar electrodes are separated from the finger electrodes connected with another bus bar electrode that is arranged so as to be parallel to this one of the bus bar electrodes, and ends in the lengthwise direction of adjacent two or more of the finger electrodes connected with each bus bar electrode are electrically connected with one another by auxiliary electrodes. With this configuration, while disadvantage due to disconnection is solved, a high fill factor, a high conversion efficiency, and small cell warpage are achieved, whereby the manufacturing yield is improved. Further, this does not involve increases in costs, and high long-term reliability is achieved. Thus, a solar cell module made up of the solar cells maintains high output.