Conductive Paste with Crystalline Tellurium Oxide for Solar Cell Firing
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Solution Overview
Problem
Conductive pastes for solar cells face challenges in achieving a balance between low contact resistance and preserving the p-n junction integrity, with glass frits requiring high energy for melting and dissolution, and existing alternatives not fully addressing these needs.
Innovation Solution
A conductive paste comprising an inorganic particle mixture of substantially crystalline particles of two or more different metal compounds, including TeO2, which replaces glass frit, allowing for similar firing profiles and manufacturing methods while reducing energy demands and preserving junction integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If glass frit is used in conductive paste to bond the conductive track to the semiconductor wafer, then bonding strength is improved, but excessive etching of the anti-reflective layer occurs which damages the p-n junction
Solution Approach 1:
The invention changes the chemical composition parameters of the glass frit by incorporating specific metal compounds (Bi2O3, TeO2, ZnO, MoO3, Li2CO3, Na2CO3) in controlled ratios. This composition optimization allows the glass frit to achieve adequate bonding strength while reducing excessive etching of the anti-reflective layer, thereby protecting the p-n junction integrity.
Solution Approach 2:
The invention uses a composite glass frit system combining multiple metal compounds (bismuth oxide, tellurium oxide, zinc oxide, molybdenum oxide, lithium carbonate, sodium carbonate) rather than a single material. This composite approach enables synergistic effects where each component contributes to bonding while the combination controls etching aggressiveness, resolving the contradiction between bonding strength and junction protection.
2Reliability
If glass frit is used to provide adequate etching of the anti-reflective layer, then contact resistance is reduced, but the p-n junction is disrupted and solar energy conversion ability decreases
Solution Approach 1:
The invention optimizes the chemical composition parameters of the glass frit, specifically incorporating Bi2O3 (10-30 wt%), TeO2 (10-30 wt%), ZnO (10-30 wt%), MoO3 (5-20 wt%), Li2CO3 (5-20 wt%), and Na2CO3 (5-20 wt%). This parameter optimization enables the glass frit to provide sufficient etching to reduce contact resistance while controlling the etching process to avoid disrupting the p-n junction.
Solution Approach 2:
The invention applies local quality by creating a controlled etching zone where the glass frit selectively removes the anti-reflective layer only in the contact area needed for electrical connection. The optimized composition allows etching to occur locally at the conductive track-semiconductor interface without affecting the broader p-n junction structure, thus maintaining junction integrity while achieving low contact resistance.
3Strength
If glass frit is used to bond the conductive track to the semiconductor wafer, then bonding is achieved, but high energy is required for melting and dissolution during firing
Solution Approach 1:
The invention changes the melting point parameters of the glass frit by incorporating low-melting-point metal compounds such as Li2CO3, Na2CO3, Bi2O3, and TeO2. These compounds lower the overall melting temperature of the glass frit system, enabling bonding to occur at reduced firing temperatures and thus reducing the energy required for melting and dissolution during the firing process.
Solution Approach 2:
The invention utilizes the oxidizing properties of metal carbonates (Li2CO3, Na2CO3) and metal oxides (Bi2O3, TeO2, ZnO, MoO3) that accelerate the chemical reactions during firing. These compounds facilitate rapid decomposition and reaction at lower temperatures, reducing the energy input needed to achieve complete bonding between the conductive track and semiconductor wafer.
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 crystalline particle mixtures in conductive pastes achieves lower contact resistance without damaging the p-n junction, offering improved efficiency and reduced energy consumption in the manufacturing process.
Implementation Method 1
firing the applied conductive paste on the surface of the substrate with a firing profile in which the temperature of the surface of the applied conductive paste exceeds 500°C for a period of two minutes or less, to produce a conductive track or coating comprising a conductive layer formed from the particles of electrically conductive material and an amorphous oxide layer formed from the inorganic particle mixture
Data Source
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AI summary
The invention relates to a process for forming a conductive track or coating on a substrate, comprising: applying a conductive paste to the substrate, the conductive paste comprising a solids portion dispersed in an organic medium, the solids portion comprising particles of electrically conductive material and an inorganic particle mixture comprising substantially crystalline particles of two or more different metal compounds, wherein the inorganic particle mixture includes substantially crystalline particles of a tellurium compound and is substantially lead free; and firing the applied conductive paste on the surface of the substrate with a firing profile in which the temperature of the surface of the applied conductive paste exceeds 500ºC for a period of two minutes or less. The invention further relates to a substrate having a conductive track or coating formed thereon.