Multiple Discrete Frits for Solar Cell Metallization
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Solution Overview
Problem
Current metallization pastes for solar cells, particularly those using lead-tellurium chemistries, are limited in controlling ARC dissolution reactions during firing, which affects the quality of electrical contact and overall solar cell efficiency, especially for advanced architectures like PERC, PERL, and PERT.
Innovation Solution
A thick-film, screen-printable paste with an inorganic frit system comprising multiple discrete frits, each containing lead and tellurium, allowing for precise control of frit chemistry to optimize ARC etching and minimize damage to the silicon emitter, thereby improving contact resistivity and solar cell efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead-tellurium based frits are used in metallization paste, then contact resistivity is reduced and electrical contact quality is improved, but control over ARC dissolution reactions is limited
Solution Approach 1:
The patent divides the single frit system into multiple discrete frits (at least two different frits), each with specific chemical compositions. This segmentation allows independent optimization of different functions: one frit can be optimized for ARC dissolution while another is optimized for electrical contact quality, thereby resolving the contradiction between contact resistivity and dissolution control.
Solution Approach 2:
The patent changes the chemical composition parameters of the frit system by using multiple discrete frits with different chemistries (e.g., different ratios of PbO, SiO2, Al2O3, and other oxides). This enables precise control over the liquid phase flux chemistry during firing, allowing independent optimization of ARC etching rate and electrical contact properties.
2Ease of manufacture
If single frit systems are used in metallization paste, then paste formulation is simple, but solar cell efficiency improvement is limited
Solution Approach 1:
The patent segments the frit system into multiple discrete components that can be independently formulated and then combined. While this increases formulation complexity slightly, it enables precise control over chemical reactions during firing, achieving efficiency improvements of 0.1% or more absolute, which far outweighs the minor increase in manufacturing complexity.
3Reliability
If aggressive ARC etching is performed during firing, then electrical contact is improved, but damage to silicon emitter increases
Solution Approach 1:
The patent uses multiple discrete frits where one frit can be designed for aggressive ARC dissolution while another frit is designed to protect the silicon emitter. The segmented system allows the beneficial etching action to occur while the protective frit mitigates damage to the underlying silicon structure.
Solution Approach 2:
The patent introduces an intermediary frit system that mediates between the silver paste and the silicon emitter. The multiple frits create a controlled liquid phase flux that facilitates ARC dissolution while simultaneously protecting the silicon emitter from excessive damage, acting as a buffer between the etching process and the sensitive semiconductor material.
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
The use of multiple discrete frits in the paste enhances solar cell performance by achieving a tenth of a percent absolute efficiency improvement or more, with superior performance compared to single frit systems, by precisely controlling the chemical composition of the liquid phase flux during the firing process.
Implementation Method 1
the frit forms a highly wetting liquid phase flux that helps sinter the metal particles and etches through an electrically insulating SiNx:H antireflective coating (ARC) to allow the metallic conductor, e.g., silver, to make electrical contact with the underlying silicon emitter
Implementation Method 2
the ARC under the conductor line must be removed (dissolved/etched) during the firing process
Implementation Method 3
the frit in the metallization paste forms a low viscosity liquid-phase flux which migrates by capillary action to the silver-silicon interface region where it facilitates the dissolution of the SiNx:H ARC layer
Implementation Method 4
the frit forms a highly wetting liquid phase flux that helps sinter the metal particles
Implementation Method 5
Electrical contact is thought to occur by an electron tunneling process through the interfacial films
Implementation Method 6
the paste is screen printed onto the front-side of a silicon wafer, dried at moderate temperature, and then rapidly fired at relatively high temperature (∼800° C.) in an infrared belt furnace
Data Source
AI summary
Devices, methods, and systems are described for thick-film paste with multiple discrete frits. The paste may be applied to contacting crystalline silicon solar cell emitter surfaces. Each frit contains both lead and tellurium. The described multiple discrete frit paste has superior solar cell performance compared with single frit pastes made from the individual discrete frits that make-up the multiple frit paste.