Inline Electroless Plating for Solar Cell Metallization
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Solution Overview
Problem
Conventional metallization methods for silicon solar cells, such as screen printing with lead-based glass frit, result in high contact resistance, large contact area, and environmental concerns, limiting efficiency and process flexibility.
Innovation Solution
The development of inline methods using electroless plating with a printer to deposit contact metal layers through openings in the passivation layer, allowing for low contact resistance and reduced contact area, and the use of lead-free glass frit, enabling efficient and environmentally friendly metallization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If screen printing with lead-based glass frit is used for metallization, then the process is robust and cost-effective, but contact resistivity is very large (10^-3 Ω·cm2) and environmental concerns arise
Solution Approach 1:
The metallization process is segmented into two distinct stages: first forming contact openings through the passivation layer to create direct contact paths, then depositing metal layers within these openings. This segmentation eliminates the need for glass frit to create contact paths, thereby reducing contact resistivity while maintaining process simplicity.
Solution Approach 2:
The harmful lead-based glass frit is extracted and removed from the metallization process. Instead of relying on glass frit to dissolve and create contact paths, the invention uses controlled opening formation and direct metal deposition, eliminating the source of high contact resistivity and environmental contamination.
2Ease of manufacture
If glass frit is used to dissolve passivation layer and create contact paths, then metal contacts can be formed, but contact area is large and efficiency is reduced
Solution Approach 1:
The passivation layer is selectively removed only at the contact openings where metal contact is needed, while the rest of the surface maintains its passivation for optimal electrical performance. This localized approach minimizes contact area to exactly what is needed, reducing surface recombination and improving efficiency while maintaining contact formation capability.
3Reliability
If heavy doping is used to reduce contact resistance, then electrical contact is improved, but minority carrier lifetime is reduced and blue response is limited
Solution Approach 1:
Contact openings are formed through the passivation layer before metal deposition, creating pre-defined contact paths that require minimal doping. This preliminary action allows for optimized doping levels that maintain both good electrical contact and high carrier lifetime, as the contact paths are established by physical openings rather than relying on heavily doped regions.
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 improves the absolute efficiency of silicon solar cells by about 1%, corresponding to a relative improvement of 7%, while reducing manufacturing costs and environmental impact.
Implementation Method 1
selectively printing electroless plating solution on the plurality of contact openings to deposit the contact metal layer
Implementation Method 2
using a laser to remove portions of the passivation layer to form contact openings
Implementation Method 3
an infrared radiation heater may be used to heat the substrate as the substrate moves along the manufacturing line
Data Source
AI summary
Inline methods for forming a photovoltaic cell electrode structure, wherein the photovoltaic cell includes a semiconductor substrate having a passivation layer thereon, includes providing a plurality of contact openings through the passivation layer to the semiconductor substrate, selectively plating a contact metal into the plurality of contact openings by printing electroless plating solution into the plurality of contact openings to deposit the contact metal, depositing a metal containing material on the deposited contact metal, and firing the deposited contact metal and the deposited metal containing material. The metal containing material may include a paste containing a silver or silver alloy along with a glass frit and is substantially free to completely free of lead. The methods may also use light activation of the passivation layer or use seed layers to assist in the plating.