Lead-Free Aluminum Paste for Solar Cells
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Solution Overview
Problem
Existing aluminum-based pastes for solar cells contain toxic heavy metals, leading to environmental and health concerns, and they struggle to maintain consistent open circuit voltage and structural integrity across varying paste weights, causing bowing and defects in solar cells.
Innovation Solution
A novel aluminum-based paste composition comprising aluminum powder, glass frits, and an organo-aluminate compound, with a fine grind size and specific particle size distribution, which is lead-free and optimized for consistent performance and reduced bowing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heavy metals are added to aluminum-based paste to increase solar cell efficiency and open circuit voltage, then electrical performance is improved, but environmental safety and health safety deteriorate due to toxicity
Solution Approach 1:
The patent removes heavy metal elements (lead, cadmium, mercury, etc.) from the aluminum-based paste composition while maintaining the desired electrical performance through alternative compositional adjustments, thereby eliminating toxicity without sacrificing open circuit voltage
Solution Approach 2:
The patent modifies the compositional parameters of the aluminum-based paste by adjusting the ratios and types of aluminum powder, glass frit, and organic vehicle to achieve the same electrical performance previously obtained only with heavy metal additives
2Adaptability or versatility
If varying amounts of aluminum paste are applied to solar cells of different sizes, then coverage requirements are met, but open circuit voltage becomes inconsistent
Solution Approach 1:
The patent optimizes specific compositional parameters including aluminum powder particle size distribution (D10: 2-5 μm, D50: 6-10 μm, D90: 12-20 μm), glass frit composition, and organic vehicle properties to create a paste that maintains consistent electrical performance across varying application weights and cell sizes
3Ease of manufacture
If aluminum paste is applied to thinner semiconductor substrates to reduce cost, then manufacturing cost is reduced, but structural integrity deteriorates due to bowing
Solution Approach 1:
The patent creates a multi-modal particle size distribution with specific ranges for different particle sizes, where finer particles fill voids and coarser particles provide structural framework, resulting in a paste that adheres well to thin substrates without causing excessive bowing
Solution Approach 2:
The patent formulates a composite aluminum-based paste combining aluminum powder with specific glass frit compositions and organic vehicles, creating a material that balances adhesion, flow, and structural support properties to prevent bowing in thin substrates
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 novel paste composition achieves consistent open circuit voltage, reduced bowing, and improved structural integrity, while being environmentally friendly and cost-effective, with enhanced water resistance and electrical efficiency.
Implementation Method 1
Firing also causes a p+ layer (i.e., impurity layer) to form by diffusion of aluminum atoms into the p-type wafer. The Al—Si layer and p+ layer secures ohmic contact between the p-type wafer and the back-side electrode.
Implementation Method 2
The Al—Si layer and p+ layer secures ohmic contact between the p-type wafer and the back-side electrode. The Al—Si layer also prevents recombination of electrons since excited electrons in the conduction band of the semiconductor are prevented from falling back into empty states in the valence band. By so doing, a back surface field (BSF) effect improves energy conversion efficiency of the solar cell by increasing the collection efficiency of generated carriers.
Data Source
AI summary
The present invention describes an aluminum-based paste composition including an aluminum powder, one or more glass frits, an organo-aluminate compound; and an organic vehicle. The present invention also describes a solar cell including an aluminum-based paste composition applied on a back surface of a silicon wafer.