Solar Cell Conductive Paste Adhesion Resistance Trade-off
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Solution Overview
Problem
Conductive pastes for solar cell electrodes face challenges in achieving both low resistance and high adhesion, with conventional methods often resulting in a trade-off between electrical resistance and adhesive strength, particularly in shallow-emitter type solar cells where ensuring both conductivity and adhesion is more difficult.
Innovation Solution
A conductive paste comprising conductive powder, organic medium, and glass frit with a specific composition of 20 wt %-80 wt % glass containing at least PbO and 80 wt %-20 wt % glass containing at least Bi2O3, which includes SiO2, Al2O3, and B2O3, is used, allowing for a balance of low series resistance and high adhesive strength by varying the mixing proportions of glass frit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If glass frit is added to conductive paste to obtain sufficient adhesive strength, then adhesive strength is improved, but glass frit softens and flows during firing resulting in increased electrode resistance
Solution Approach 1:
The invention changes the chemical composition parameters of the glass frit by specifying precise ranges of SiO2 (30-70 wt%), Al2O3 (5-20 wt%), and B2O3 (5-20 wt%), along with controlled amounts of PbO (0.1-10 wt%) and Bi2O3 (0.1-10 wt%). These parameter adjustments optimize the softening behavior and electrical properties of the glass frit to simultaneously achieve adequate adhesion and low electrode resistance
Solution Approach 2:
The invention uses a composite glass frit system combining multiple oxide components (SiO2, Al2O3, B2O3, PbO, Bi2O3) rather than a single glass type. This composite approach allows the glass frit to exhibit both strong adhesive properties and controlled softening behavior that prevents excessive flow and insulating layer formation during firing
2Reliability
If the amount of glass frit is lowered to avoid softening and flow, then electrode resistance is reduced, but adhesive strength between electrode and substrate is reduced
Solution Approach 1:
The invention optimizes the glass frit composition parameters to achieve maximum adhesive strength with minimal glass frit content (0.1-5 wt%). The specific oxide ratios, particularly high SiO2 content combined with controlled Al2O3 and B2O3, enhance the bonding efficiency per unit weight of glass frit, allowing low resistance without sacrificing adhesion
3Reliability
If firing temperature is lowered to prevent glass frit softening and flow, then electrode resistance is reduced, but adhesive strength and dissolution of insulating protective film are reduced
Solution Approach 1:
The invention adjusts the glass frit composition to shift the softening temperature range to lower values while maintaining adhesive performance. The inclusion of PbO and Bi2O3, along with optimized B2O3 content, lowers the melting point of the glass frit, enabling effective adhesion and film dissolution at reduced firing temperatures without causing excessive flow that would increase resistance
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 proposed solution effectively reduces series resistance and enhances adhesive strength, improving the overall electrical performance and mechanical reliability of solar cell electrodes, as demonstrated by optimal results when the glass containing PbO is between 20% and 80% and glass containing Bi2O3 is between 20% and 65% by weight.
Implementation Method 1
glass frits often soften and flow during the firing process and become segregated in the interface between the substrate and electrode
Implementation Method 2
an insulating protective film is sometimes formed on the surface of semiconductor substrates in solar cells, and a conductive paste in which glass frit is added is used also as the conductive paste used on the protective film, so that the insulating protective film is dissolved away during firing
Implementation Method 3
Glass frit is added to the conductive paste used in silicon solar cells such as the above to obtain sufficient adhesive strength on the substrate even when the firing time is short
Data Source
AI summary
To obtain low resistance and high adhesion at the same time in a solar cell electrode, a conductive paste is offered. A conductive paste for solar cell electrode contains conductive powder, organic medium and glass frit which is mixture of more than one kind of glass frit such as a mixture of glass frit containing at least PbO and glass frit containing at least Bi2O3.