Aluminum Paste Particle Shape for Solar Cell Bowing Reduction
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Solution Overview
Problem
Silicon solar cells with aluminum back electrodes exhibit undesirable bowing behavior, leading to cracking and processing issues, especially with large or thin silicon wafers, which affects their durability and manufacturing efficiency.
Innovation Solution
Aluminum pastes comprising a specific weight ratio of spherical-shaped and nodular-shaped aluminum powder, along with an organic vehicle and optional glass frit compositions, are used to form p-type aluminum back electrodes, reducing bowing and improving adhesion and electrical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional aluminum paste is used to form aluminum back electrodes, then the electrode can be formed, but the silicon solar cells exhibit undesirable bowing behavior leading to cracking and processing issues
Solution Approach 1:
The invention changes the particle shape parameter of aluminum powder from conventional irregular shapes to predominantly spherical shapes (greater than 50% spherical particles by weight). This parameter change in the paste composition directly reduces the bowing behavior of silicon solar cells while maintaining electrode functionality and improving durability.
Solution Approach 2:
The invention uses a composite aluminum paste composition containing spherical aluminum powder particles combined with specific binders and solvents. This composite material approach creates a paste that forms aluminum back electrodes with reduced bowing effects, preventing cracking and processing issues while maintaining electrical conductivity.
2Productivity
If aluminum paste is screen printed and fired to form aluminum back electrodes, then the back surface field layer is formed, but bowing behavior causes cracking and affects manufacturing efficiency
Solution Approach 1:
By changing the particle morphology parameter to spherical shapes and optimizing the paste composition with specific binders and solvents, the invention reduces bowing during the screen printing and firing process. This enables continuous manufacturing without interruptions from cracking, thereby improving productivity.
3Strength
If aluminum paste is used to form back electrodes, then electrical conductivity is achieved, but bowing behavior leads to cracking that compromises structural integrity
Solution Approach 1:
The invention changes the particle shape parameter to spherical aluminum powder particles, which pack more uniformly and create more consistent thermal and mechanical properties during firing. This parameter change reduces differential stress and bowing, preventing cracking while maintaining the electrical conductivity needed for back electrode functionality.
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 use of these aluminum pastes results in silicon solar cells with low bowing behavior, good electrical performance, and enhanced durability by ensuring uniform Al-Si eutectic layers and improved adhesion between the aluminum back electrode and the silicon wafer substrate.
Implementation Method 1
molten aluminum from the paste dissolves the silicon during the firing process
Implementation Method 2
forming an aluminum-silicon melt
Implementation Method 3
an epitaxially grown layer of silicon is formed that is doped with aluminum
Implementation Method 4
an aluminum paste is generally screen printed and dried on the back-side of the silicon wafer
Data Source
AI summary
Described are aluminum pastes comprising spherical-shaped and nodular-shaped particulate aluminum and an organic vehicle and their use in forming p-type aluminum back electrodes of silicon solar cells.