Solar Cell Conductive Paste Composition for Ohmic Contact
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Solution Overview
Problem
Conventional solar cell electrode pastes, particularly those using lead-free tellurium glass, face challenges in achieving uniform ohmic contact and maintaining high bonding strength, leading to poor performance under EL inspection and reduced reliability.
Innovation Solution
A conductive paste composition combining tellurium-bearing lead-free glass with lithium and bismuth as essential components, and tellurium-free lead silicate glass, with a mass ratio of 2:8 to 8:2, is used to form a surface electrode, ensuring good ohmic contact and bonding strength while passing EL inspection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If lead-free tellurium glass is used in conductive paste, then environmental compliance and toxicity reduction are improved, but uniformity of ohmic contact and bonding strength deteriorate
Solution Approach 1:
The patent changes the chemical composition parameters of the glass powder by introducing specific ratios of Li2O (1-5 wt%), Bi2O3 (0.5-3 wt%), and TeO2 (0.1-1 wt%), along with controlled amounts of PbO (0-5 wt%). These parameter adjustments optimize the melting characteristics and reactivity of the glass, enabling uniform ohmic contact while maintaining lead-free or low-lead formulation for environmental compliance.
Solution Approach 2:
The patent creates a composite glass system combining multiple oxide components (Li2O, Bi2O3, TeO2, PbO, SiO2, B2O3) that work synergistically. This composite material approach allows the glass to exhibit improved wetting properties, controlled viscosity, and enhanced reactivity with the semiconductor substrate, achieving both environmental compliance and reliable electrical contact.
2Manufacturing precision
If tellurium glass is used to etch antireflection film, then fire through capability is improved, but excessive etching of semiconductor substrate occurs
Solution Approach 1:
The patent adjusts the composition parameters to control the etching rate and selectivity. By optimizing TeO2 content (0.1-1 wt%) and combining it with SiO2 (1-10 wt%) and B2O3 (1-5 wt%), the glass achieves appropriate viscosity and chemical reactivity that enables complete penetration of the antireflection film while self-limiting the etching depth to prevent excessive substrate damage.
Solution Approach 2:
The glass powder acts as an intermediary material that facilitates controlled interaction between the conductive paste and the layered structure (antireflection film + semiconductor substrate). The glass composition is designed to preferentially react with and etch the antireflection film while being less aggressive toward the semiconductor substrate, enabling selective fire-through capability.
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 paste composition achieves better EL inspection results, higher conversion efficiency, and excellent bonding strength, addressing the limitations of previous lead-free glass compositions by maintaining a narrow firing temperature window and preventing black spots or cloudy spots during EL inspection.
Implementation Method 1
During firing process, electrode material is heated and melted and dissolved the antireflection film in contact area with the electrode material
Implementation Method 2
electrode material is heated and melted and dissolved the antireflection film
Implementation Method 3
It increases the amount of silver dissolved in glass to decrease contact resistance
Implementation Method 4
During the cooling of firing process, tellurium can inhibit precipitation of silver
Implementation Method 5
tellurium can inhibit precipitation of silver. Therefore, it broadens the firing process window and inhibit excessive etching of semiconductor substrate
Data Source
AI summary
The invention discloses a conductive paste for forming the electrode on the surface of solar cell, which contains conductive powder, mixed glass and organic phase; wherein, the mixed glass comprises the following two types of glass components: the first type of glass is at least one selected from the tellurium glass which does not contain lead substantially and having tellurium, bismuth, lithium as the essential component;The second type of glass is at least one kind of lead silicate glass, which having lead and silicon as essential components and does not contain tellurium substantially. The invention also provides a solar cell prepared by printing the conductive paste as a surface electrode and a manufacturing method of the solar cell. The solar cell made of the conductive paste of this invention has good EL performance in inspection, excellent ohmic contact of the cell, high cell conversion efficiency, better reliability, and strong bonding strength, the adhesion performance is taken into account while improving reliability and ohmic contact.