Sub-Cell Solar Interconnection Structure for Stronger High-Voltage Panels
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Solution Overview
Problem
The fabrication of high voltage solar panels faces challenges such as metal breakages in thin metal bridges between small cells, dark area formation due to conventional soldering, and the need for strong interconnections that can withstand stress, while also requiring flexible voltage and current configurations to minimize cost and complexity.
Innovation Solution
The use of minimal plating or no plating for sub-cell metallization, screen printable solder paste to reduce dark area formation, and thick conductive ribbons for strength, along with metal seed layers and selective metallization to enable dicing and singulation of solar cell wafers without increasing module interconnections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If thin metal bridges are used to interconnect small cells, then the complexity of interconnections is reduced, but the reliability decreases due to metal breakages
Solution Approach 1:
A solder paste layer is introduced as an intermediary material between the thin metal bridge and the cell contact points. This solder paste layer acts as a mediator that strengthens the mechanical connection and electrical contact, preventing metal breakages while maintaining the simplified thin bridge structure. The solder paste is applied to the cell surface before the metal bridge is placed, creating a robust joint that withstands stress and thermal cycling.
2Strength
If conventional soldering is used for cell interconnection, then strong mechanical bonds are formed, but dark area formation occurs reducing efficiency
Solution Approach 1:
The soldering process parameters are optimized to minimize dark area formation. Specifically, the solder paste composition is adjusted with controlled particle size distribution and alloy composition, and the reflow soldering temperature profile is precisely controlled. These parameter changes enable strong metallurgical bonds while minimizing excessive solder flow and dark area formation that would otherwise occur with conventional soldering processes.
3Strength
If thick conductive ribbons are used for interconnection, then mechanical strength and stress resistance improve, but the cost and material usage increase
Solution Approach 1:
Instead of uniformly thick conductive ribbons throughout, the interconnection structure uses locally optimized thickness. The metal bridge is thin in regions where mechanical strength is less critical, and only the contact regions with solder paste application have increased thickness and material concentration. This local quality approach provides necessary stress resistance at connection points while minimizing overall metal material usage and cost.
4Ease of manufacture
If minimal plating or no plating is used for sub-cell metallization, then material cost and processing time are reduced, but the manufacturing precision and contact quality may worsen
Solution Approach 1:
The metallization structure uses a composite approach combining a thin metal seed layer (such as titanium or chromium) with a thicker solder paste layer. The seed layer provides excellent adhesion to the semiconductor substrate and serves as a nucleation site for solder bonding, while the solder paste provides the bulk of the electrical and mechanical connection. This composite structure achieves high contact quality and reliability without requiring extensive metal plating, thus maintaining manufacturing efficiency.
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 enhances the reliability and cost-effectiveness of high voltage panels by reducing metal thickness, minimizing resistive losses, and allowing for flexible voltage and current configurations, thereby improving the overall efficiency and durability of solar cells.
Implementation Method 1
Photovoltaic cells, commonly known as solar cells, are well known devices for direct conversion of solar radiation into electrical energy
Implementation Method 2
adjacent ones of the plurality of sub-cells are coupled with a corresponding metal ribbon coupled to the solder paste layer at adjacent outer perimeters of corresponding adjacent ones of the plurality of sub-cells
Data Source
AI summary
Methods of fabricating solar cells having a plurality of sub-cells coupled by cell level interconnection, and the resulting solar cells, are described herein. In an example, a solar cell includes a plurality of sub-cells. Each of the plurality of sub-cells includes a singulated and physically separated semiconductor substrate portion. Each of the plurality of sub-cells includes an on-sub-cell metallization structure interconnecting emitter regions of the sub-cell. An inter-sub-cell metallization structure couples adjacent ones of the plurality of sub-cells. The inter-sub-cell metallization structure is different in composition from the on-sub-cell metallization structure.