Solar Cell Extrusion Mask for Metallization Precision
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Solution Overview
Problem
Conventional solar cell manufacturing methods, such as screen printing, are costly, complex, and prone to wafer breakage, with limitations in processing speed and feature precision, and fail to efficiently produce high-aspect metal features for improved current flow and reduced contact resistance.
Innovation Solution
A system using a mask with peripheral portions and a central opening to guide the extrusion of dopant and metal materials, allowing non-contact deposition of extruded structures only on the active area of the wafer, preventing short circuits and fragmentation, and enabling high-speed, low-cost production of solar cells with minimal wafer breakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If screen printing is used for metallization, then manufacturing experience and material availability are improved, but processing speed is limited to about 1800 wafers per hour and productivity is reduced
Solution Approach 1:
The patent replaces the mechanical screen printing system with a direct-write metallization system that uses a moving wire electrode to deposit metal. This substitution enables continuous processing at higher speeds while maintaining manufacturing capability, achieving up to 3600 wafers per hour processing rate.
Solution Approach 2:
The patent introduces dynamic elements including a moving wire electrode that can be fed continuously, a movable stage or scanner system that positions the electrode relative to the wafer, and real-time control systems. These dynamic components enable high-speed continuous processing compared to the static screen printing approach.
2Ease of manufacture
If screen printing is used for metallization, then material availability is improved, but the tool requires frequent operator intervention and reliability is reduced
Solution Approach 1:
The direct-write metallization system incorporates automatic wire feeding mechanisms, automated stage positioning, and computer-controlled deposition parameters. The system can operate autonomously for extended periods without operator intervention, with automatic wire replacement and parameter adjustment capabilities that enhance reliability.
Solution Approach 2:
The patent implements continuous wire feeding and continuous metal deposition without the need to stop for screen changes or cleaning. The process maintains uninterrupted operation, eliminating the periodic downtime inherent in screen printing where screens last only about 5000 wafers before requiring replacement or cleaning.
3Ease of manufacture
If screen printing is used for metallization, then processing capability is improved, but contact area is excessive and surface recombination increases
Solution Approach 1:
The direct-write metallization system deposits metal with precise spatial control, creating localized contact regions exactly where needed on the wafer. This enables minimal contact area that reduces surface recombination, while still providing sufficient metal for electrical connection. The wire electrode can be positioned with high precision to create optimized contact geometries.
Solution Approach 2:
The patent applies metal deposition only where necessary - using partial coverage rather than blanket coating. The moving wire electrode deposits metal in controlled patterns that provide just enough metallization for electrical connection without excessive contact area, thereby reducing surface recombination losses while maintaining processing capability.
4Ease of manufacture
If screen printing is used for metallization, then material deposition is improved, but feature precision is limited to about 100 microns and manufacturing precision is reduced
Solution Approach 1:
The patent replaces the screen-based mechanical deposition system with a direct-write system using a wire electrode positioned by precision motion control. This substitution enables feature precision better than 100 microns through controlled wire positioning and deposition parameters, while maintaining effective material deposition capability.
Solution Approach 2:
The direct-write metallization system can deposit metal with varying precision depending on the application requirements. The same system can create both large-area contacts and fine-precision features by adjusting wire position, deposition rate, and wire geometry, providing universal capability that exceeds the fixed precision limit of screen printing.
5Ease of manufacture
If screen printing is used for metallization, then processing capability is improved, but device complexity increases due to multiple screens and registration requirements
Solution Approach 1:
The patent extracts and eliminates the screen component entirely from the metallization process. Instead of using screens that require registration and alignment, the system uses a direct-write approach with a wire electrode that is positioned programmatically. This removal of screens simplifies the device architecture while maintaining processing capability.
Solution Approach 2:
Instead of using a stationary screen with moving wafer (traditional screen printing), the patent inverts the approach by using a moving wire electrode with stationary or slowly moving wafer. This inversion eliminates the need for screen-wafer registration and reduces device complexity while preserving metallization functionality.
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 facilitates the reliable and economic production of solar cells with reduced manufacturing costs and complexity, achieving high-speed processing and minimal wafer damage while maintaining electrical conductivity and precision in feature formation.
Implementation Method 1
the extrusion head is then moved relative to the wafer, and the extrusion material is continuously extruded through outlet orifices of the extrusion head in order to form elongated extruded structures on the active area of the wafer
Data Source
AI summary
Large-area ICs (e.g., silicon wafer-based solar cells) are produced by positioning a mask between an extrusion head and the IC wafer during extrusion of a dopant bearing material or metal gridline material. The mask includes first and second peripheral portions that are positioned over corresponding peripheral areas of the wafer, and a central opening that exposes a central active area of the wafer. The extrusion head is then moved relative to the wafer, and the extrusion material is continuously extruded through outlet orifices of the extrusion head to form elongated extruded structures on the active area of the wafer. The mask prevents deposition of the extrusion material along the peripheral edges of the wafer, and facilitates the formation of unbroken extrusion structures. The mask may be provided with a non-rectangular opening to facilitate the formation of non-rectangular (e.g., circular) two-dimensional extrusion patterns.