Intercalation Layer for Solderable Aluminum Solar Rear Contacts
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The power conversion efficiency of solar cells is reduced when a silver layer directly contacts the silicon substrate instead of the aluminum layer, due to interdiffusion and oxidation issues during firing, which complicates the integration of silver pastes with aluminum layers in solar cell production, leading to reduced solderability and increased costs.
Innovation Solution
Development of intercalation pastes containing precious metals and intercalating particles that can be printed on aluminum layers, altering their properties during firing to create a solderable surface without significant interdiffusion, allowing for the use of standard processing conditions and integration into existing production lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silver paste is printed directly on aluminum particle layer, then solderability is improved, but interdiffusion occurs during firing reducing efficiency
Solution Approach 1:
The patent introduces an intercalation layer containing precious metal particles (silver, gold, platinum, palladium, or their alloys) as an intermediary between the aluminum particle layer and the silicon substrate. This intercalation layer prevents direct contact and interdiffusion between silver and aluminum during firing, while still providing a solderable surface for tabbing ribbon attachment. The intercalation layer acts as a mediator that resolves the contradiction by enabling solderability without allowing harmful interdiffusion.
2Manufacturing precision
If peak firing temperature is lowered to reduce interdiffusion, then layer separation is maintained, but front side silver paste cannot fire through silicon nitride
Solution Approach 1:
The patent segments the rear metallization structure into distinct functional layers: an aluminum particle layer for back-surface field formation, an intercalation layer for preventing interdiffusion and providing solderability, and maintains separate front and rear processing requirements. This segmentation allows the rear side to use lower peak firing temperatures (avoiding interdiffusion) while the front side can undergo separate high-temperature processing to fire through silicon nitride and form ohmic contact, thus resolving the contradiction between maintaining layer separation and forming reliable electrical contact.
3Reliability
If ultrasonic soldering is used to create solderable surface, then solderability is improved, but equipment complexity and tin consumption increase
Solution Approach 1:
The patent uses a printed intercalation paste containing precious metal particles as a chemical intermediary that creates a solderable surface during the standard firing process. This eliminates the need for ultrasonic soldering equipment and additional processing steps. The intercalation layer, formed through conventional screen printing and firing, provides the necessary solderability without requiring complex ultrasonic equipment or large quantities of tin, thus resolving the contradiction between achieving solderability and avoiding increased device complexity.
4Quantity of substance
If aluminum and silver layers are allowed to contact during firing, then material usage is reduced, but oxidation occurs reducing solderability
Solution Approach 1:
The patent introduces an intercalation layer as a protective intermediary between the aluminum particle layer and the environment during firing. This intercalation layer, containing precious metal particles, prevents oxidation of the aluminum and silver layers while allowing them to remain in contact for material efficiency. The intercalation layer acts as a barrier that maintains solderability by preventing oxidation, thus resolving the contradiction between using minimal materials and maintaining solderability.
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 intercalation pastes enhance the solderability of aluminum layers, reducing silver-aluminum interdiffusion, maintaining high efficiency, and enabling cost-effective, immediate integration into existing solar cell production lines without additional capital expenses.
Implementation Method 1
intercalation pastes that can be directly printed on aluminum and fired using standard solar cell processing conditions
Implementation Method 2
the aluminum and silver layers interdiffuse, and the resulting layer surface becomes oxidized and loses solderability
Implementation Method 3
fired multilayer stack... co-firing the multilayer stack
Data Source
AI summary
A method of forming a fired multilayer stack are described. The method involves the steps of a) applying a wet metal particle layer on at least a portion of a surface of a substrate, b) drying the wet metal particle layer to form a dried metal particle layer, c) applying a wet intercalation layer directly on at least a portion of the dried metal particle layer to form a multilayer stack, d) drying the multilayer stack, and e) co-firing the multilayer stack to form the fired multilayer stack. The intercalating layer may include one or more of low temperature base metal particles, crystalline metal oxide particles, and glass frit particles. The wet metal particle layer may include aluminum, copper, iron, nickel, molybdenum, tungsten, tantalum, titanium, steel or combinations thereof.