Lead-Free Bismuth-Tellurium-Oxide Paste for Solar Cell Electrodes
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Solution Overview
Problem
Conventional thick film paste compositions for solar cells contain high amounts of silver and lead, which are costly and environmentally harmful, while maintaining electrical performance remains a challenge.
Innovation Solution
A thick film paste composition comprising 35-55 wt% silver, 0.5-5 wt% lead-free bismuth-tellurium oxide, and an organic medium, where the bismuth-tellurium oxide consists of 22-42 wt% Bi2O3 and 58-78 wt% TeO2, is used to form electrodes with reduced silver content and improved adhesion properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional thick film paste compositions are used, then good electrical performance is achieved, but high silver content increases cost and high lead content causes environmental harm
Solution Approach 1:
The patent extracts and removes lead from the traditional paste composition entirely, replacing it with a lead-free bismuth-tellurium-oxide glass frit. This extraction eliminates the harmful environmental factor while maintaining the functional properties needed for electrode formation and adhesion.
Solution Approach 2:
The patent changes the chemical composition parameters by introducing bismuth-tellurium-oxide glass frit with specific Bi2O3 (22-42 wt%) and TeO2 (58-78 wt%) ratios. This parameter change enables lead elimination while maintaining or improving adhesion properties and electrical performance.
2Object-affected harmful factors
If silver content is reduced to lower cost, then manufacturing cost decreases, but electrical performance may deteriorate
Solution Approach 1:
The patent creates a composite paste composition combining silver powder with bismuth-tellurium-oxide glass frit. This composite material allows optimization of silver content for cost reduction while the glass frit matrix maintains adhesion and facilitates electrical conductivity, preventing performance deterioration.
Solution Approach 2:
The bismuth-tellurium-oxide glass frit acts as an intermediary material that binds silver particles and substrate together. It mediates between the reduced silver content and the required adhesion/electrical performance, enabling cost reduction without sacrificing functionality.
3Object-affected harmful factors
If lead-free composition is used, then environmental friendliness improves, but adhesion properties may be compromised
Solution Approach 1:
The patent changes the chemical composition by using bismuth-tellurium-oxide glass frit with specific oxide ratios. This composition change maintains adhesion strength through the glass frit's bonding properties while eliminating lead for environmental friendliness.
Solution Approach 2:
The lead-free bismuth-tellurium-oxide glass frit forms a composite material that provides adhesion functionality traditionally associated with lead-containing pastes. The glass frit matrix binds particles and substrate effectively without requiring lead.
Data Source
AI summary
The present invention is directed to an electroconductive thick film paste composition comprising Ag and a Pb-free bismuth-tellurium-oxide both dispersed in an organic medium. The present invention is further directed to an electrode formed from the paste composition and a semiconductor device and, in particular, a solar cell comprising such an electrode. The present invention is also directed to the bismuth-tellurium oxide that is a component of thick film pastes.