Alloy Aluminum Paste Composition for Void-Free PERC Rear Contacts
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Solution Overview
Problem
PERC solar cells face challenges with voids in the aluminum back surface field, leading to increased contact resistance and reduced fill factor due to silicon dissolution into conventional aluminum pastes, resulting in low gap filling rates and irregular BSF layers.
Innovation Solution
An alloy aluminum paste composition comprising 35-56.5% aluminum-silicon alloy powder, 17.5-37.5% aluminum powder, 1-2% lead-free glass powder, 15-20% organic solvent, 3-5% ethyl cellulose, 0.05-0.1% thixotropic agent, and 0.5-1.5% dispersant, with specific particle sizes and oxygen content, is used to improve filling rates and form uniform BSF layers on PERC solar cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional aluminum paste is used for metallization on PERC cell rear, then the paste can be applied easily, but silicon dissolves into the aluminum paste forming voids leading to increased contact resistance and reduced fill factor
Solution Approach 1:
The patent uses a composite paste formulation containing aluminum powder, aluminum-silicon alloy powder, and glass powder in specific ratios. The aluminum-silicon alloy powder (35-56.5 wt%) with controlled silicon content prevents excessive silicon dissolution into the aluminum matrix, while the glass powder (1-2 wt%) forms a protective barrier during sintering, eliminating voids and improving contact reliability without compromising ease of application
Solution Approach 2:
The patent optimizes multiple parameters including the silicon content in aluminum-silicon alloy powder (11-22 wt%), particle size distribution (D50 values), oxygen content (0.3-0.45 wt%), and paste composition ratios. These parameter adjustments control the metallization reaction kinetics, preventing void formation while maintaining good paste applicability and screen printing characteristics
2Reliability
If the opening on rear coating is reduced to 0.5-1% of solar cell area, then the passivation effect is improved, but the gap filling rate becomes low and the BSF layer becomes irregular
Solution Approach 1:
The patent creates localized material properties within the paste composition, using aluminum-silicon alloy powder with specific silicon content (11-22 wt%) in the metal contact regions to enhance gap filling capability, while maintaining aluminum powder with controlled oxygen content (0.35-0.45 wt%) for uniform BSF layer formation. This local material optimization enables effective filling of small openings (0.5-1% area) without compromising passivation in non-contact regions
Solution Approach 2:
The patent adjusts critical parameters including the ratio of aluminum-silicon alloy powder to aluminum powder (1:1 to 3:1), particle size distributions (D50 values), and oxygen content to control paste rheology and sintering behavior. These parameter optimizations enable complete gap filling in minimal openings while forming regular, uniform BSF layers even at 0.5-1% opening ratios, maintaining both passivation effectiveness and manufacturing precision
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 alloy paste achieves a high gap filling rate, forms a regular BSF layer, reduces aluminum beads, and provides excellent adhesion and aging resistance, enhancing the photoelectric conversion efficiency of PERC solar cells to 22.26-22.42%.
Implementation Method 1
the aluminum-silicon alloy powder has a median particle size D50 of 5-6 μm and an oxygen content of 0.3-0.4 wt %; the aluminum powder has a median particle size D50 of 7-8 μm, and an oxygen content of 0.35-0.45 wt %
Implementation Method 2
a lead-free glass powder 1-2%
Implementation Method 3
an organic solvent 15-20%; ethyl cellulose 3-5%
Data Source
AI summary
Based on 100 wt % of the alloy aluminum paste, the alloy aluminum paste includes the following components in percentages by weight: 35-56.5% of an aluminum-silicon alloy powder, 17.5-37.5% of an aluminum powder, 1-2% of a lead-free glass powder, 15-20% of an organic solvent, 3-5% of ethyl cellulose, 0.05-0.1% of a thixotropic agent and 0.5-1.5% of a dispersant. The alloy paste can be applied to a PERC solar cell having a passivation coating opening consisting of 0.5-1% of the area of the solar cell. When the alloy aluminum paste is applied to a PERC solar cell having a low opening rate, particularly a rear electrode having a passivation coating opening consisting of 0.5-1% of the area of the solar cell.