Encapsulated Copper Paste Metallization for Solar Cells
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Solution Overview
Problem
Conventional silver-based metallization in silicon solar cells is costly, and copper deposition processes are difficult to integrate into manufacturing due to fragility of substrates and high costs associated with inert atmospheres and patterning steps, leading to inefficiencies and increased expenses.
Innovation Solution
A copper metallization paste with encapsulated copper-containing particles coated with multiple layers of materials like silver, nickel, titanium, and tungsten, which can be screen printed and sintered to form conductive contact structures, reducing oxidation and diffusion issues while maintaining low contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If silver-based metallization is used, then good electrical conductivity and ease of manufacture are achieved, but manufacturing cost increases significantly
Solution Approach 1:
The invention changes the material parameter from silver to copper, which has lower cost while maintaining comparable electrical conductivity. The copper paste is formulated with specific organic vehicles and glass frits to match the processing parameters of conventional silver pastes, enabling direct substitution without major process changes.
Solution Approach 2:
The invention replaces expensive silver with cheaper copper material. The copper paste is designed to be used in a single firing process where the organic components are burned off and the copper is sintered into the final contact structure, eliminating the need for expensive precious metals.
2Quantity of substance
If copper deposition processes are used, then manufacturing cost decreases, but device complexity and difficulty of manufacture increase due to additional patterning steps and inert atmosphere requirements
Solution Approach 1:
The copper paste is designed to serve multiple functions: it provides the conductive metal, contains glass frits for adhesion and sintering aid, and includes organic vehicles for screen printing. This multi-functional formulation allows the paste to be processed using existing screen printing equipment without requiring separate patterning steps or inert atmosphere facilities.
Solution Approach 2:
The invention introduces glass frit particles as an intermediary material that facilitates the bonding between copper and silicon during the firing process. The glass frit softens at firing temperature, creating a adhesive matrix that holds the copper particles together and to the substrate, eliminating the need for complex adhesion control procedures.
3Quantity of substance
If copper metallization is used, then manufacturing cost decreases, but reliability worsens due to copper oxidation and diffusion issues
Solution Approach 1:
The copper paste is formulated with glass frits and organic binders that are designed to undergo controlled decomposition and reaction during the firing process. The organic components burn off first, creating a reducing atmosphere that prevents copper oxidation, followed by glass frit softening that encapsulates the copper particles and prevents diffusion before the copper can migrate into the silicon.
Solution Approach 2:
The invention converts the potential harm of copper oxidation into a benefit by designing the organic vehicle components to decompose and create a reducing atmosphere during firing. This self-generated reducing environment protects the copper from oxidizing, turning what would be a harmful oxidation reaction into a protective measure.
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 solution enables cost-effective copper contact structures compatible with current manufacturing processes, reducing solar cell production costs and maintaining efficiency by preventing copper diffusion and oxidation, thus enhancing the reliability and performance of solar cells.
Implementation Method 1
The glass frit particles soften during heating, such as during a 'firing' step (a short high-temperature anneal) to hold the silver particle matrix together and to the silicon substrate
Implementation Method 2
The organic resins are generally burned off during the firing step
Implementation Method 3
heating the copper metallization paste to form a copper layer
Data Source
Figure 1~2C
Figure 3~6
Figure 4A~4B
AI summary
Embodiments of the invention generally provide copper contact structures on a solar cell formed using copper metallization pastes and/or copper inks. In one embodiment, the copper metallization paste includes an organic matrix, glass frits within the organic matrix, and a metal powder within the organic matrix, the metal powder comprising encapsulated copper-containing particles. The encapsulated copper-containing particles further include a copper-containing particle and at least one coating surrounding the copper-containing particle. In another embodiment, a solar cell includes a front contact structure on a substrate comprising a doped semiconductor material. The front contact structure includes a copper layer comprising sintered encapsulated copper-containing particles, wherein at least some of the encapsulated copper-containing particles include a copper-containing particle and at least one coating surrounding the copper-containing particle.