Bismuth-Tellurium-Oxide Thick Film 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 hazardous, while maintaining electrical and mechanical performance remains a challenge.
Innovation Solution
A thick film paste composition comprising 25-55 wt % electrically conductive silver, 5-35 wt % nickel or aluminum, and 0.5-5 wt % lead-free bismuth-tellurium-oxide dispersed in an organic medium, which reduces silver usage and eliminates lead, forming electrodes with good electrical and adhesion properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional thick film paste compositions are used, then high electrical conductivity is achieved, but high silver content increases cost and lead content creates environmental hazards
Solution Approach 1:
The patent changes the chemical composition parameters by introducing bismuth-tellurium-oxide as a new component and adjusting the ratios of silver, nickel, and other metals. This parameter change allows reduction of silver content from conventional high levels to 25-55 wt% while maintaining electrical conductivity through the synergistic effect of bismuth-tellurium-oxide and other conductive metals in the paste composition
Solution Approach 2:
The patent creates a composite paste material combining multiple components: silver (25-55 wt%), nickel (5-35 wt%), bismuth-tellurium-oxide (0.5-5 wt%), and other additives. This composite formulation achieves the desired electrical conductivity and adhesion properties while reducing reliance on high silver content, thereby lowering cost and environmental impact
2Ease of manufacture
If lead is used in thick film paste, then manufacturing process stability is maintained, but environmental hazards increase
Solution Approach 1:
The patent extracts and removes lead from the paste composition entirely, replacing it with bismuth-tellurium-oxide as the functional equivalent. This extraction eliminates the environmental hazard associated with lead while maintaining the firing process stability and adhesion properties through the new bismuth-tellurium-oxide component
Solution Approach 2:
The patent substitutes expensive and hazardous lead with more environmentally friendly bismuth-tellurium-oxide, creating a disposable-friendly formulation that meets modern environmental regulations without compromising manufacturing stability or requiring complex disposal procedures
3Quantity of substance
If silver content is reduced, then cost decreases, but electrical conductivity and adhesion performance deteriorate
Solution Approach 1:
The patent merges multiple conductive components (silver, nickel, bismuth-tellurium-oxide) into a synergistic formulation where each component contributes to the overall electrical conductivity. This combination allows reduction of silver content while maintaining total conductivity through the complementary effects of the other conductive materials in the paste
Solution Approach 2:
The patent changes the compositional parameters by introducing bismuth-tellurium-oxide and optimizing the ratios of conductive metals, transforming the paste from a silver-dependent formulation to a multi-component conductive system that achieves comparable or superior electrical properties with reduced silver content
4Ease of manufacture
If thick film paste is fired at high temperature, then electrode formation is achieved, but silver migration and adhesion issues occur
Solution Approach 1:
The patent introduces bismuth-tellurium-oxide as an intermediary component that mediates between the metal particles and the substrate during firing. This intermediary material promotes stable adhesion and prevents excessive silver migration by controlling the interaction between the conductive metals and the substrate at high temperatures
Solution Approach 2:
The patent creates a composite paste material where bismuth-tellurium-oxide and other additives work together with the metal particles to achieve stable electrode formation. This composite formulation maintains adhesion stability during high-temperature firing by distributing thermal stress and controlling metal particle behavior through the synergistic effects of its components
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 composition achieves reduced silver content and eliminates lead, maintaining electrical and mechanical performance, while providing cost savings and environmental benefits by forming electrodes with enhanced adhesion and efficiency.
Implementation Method 1
the paste composition has been fired to remove the organic medium and form the electrode
Implementation Method 2
forming electrodes with enhanced adhesion and efficiency
Implementation Method 3
the paste composition has been fired to remove the organic medium
Implementation Method 4
electrically conductive Ag, the second electrically conductive metal and the bismuth-tellurium-oxide
Data Source
AI summary
The present invention is directed to an electroconductive thick film paste composition comprising electrically conductive Ag, a second electrically conductive metal selected from the group consisting of Ni, Al and mixtures thereof and a Pb-free bismuth-tellurium-oxide all dispersed in an organic medium. The present invention is further directed to an electrode formed from the thick film paste composition and a semiconductor device and, in particular, a solar cell comprising such an electrode.