Multi-Layer Solar Cell Electrode with Graded Silver Particle Size
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Solution Overview
Problem
Conventional methods for forming high-aspect-ratio electrodes on semiconductor substrates, such as those used in solar cells, often result in electrode breakage due to silver particle contraction during sintering, and suffer from issues like foaming, cracking, and incomplete combustion, which degrade the electrode's performance.
Innovation Solution
A multi-layered electrode structure is formed using a conductive paste with a total silver content of 75 wt% to 95 wt% and silver particles with an average diameter of 4 µm to 8 µm, where the upper electrode layer has a higher silver particle content than the first electrode layer, along with specific organic vehicle decomposition temperatures and viscosity ranges to prevent contraction and ensure printability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a thick electrode with fine line width (high aspect ratio) is formed by conventional screen-printing, then the electrode can achieve low resistance and small occupation area, but the electrode structure becomes complex and difficult to form in a single printing
Solution Approach 1:
The electrode is divided into multiple layers (first electrode layer and upper electrode layer) with different silver particle size distributions. The first layer uses finer particles (0.5-4 μm) for good substrate contact, while the upper layer uses coarser particles (4-8 μm) for structural stability and low resistance, achieving high aspect ratio without excessive complexity
Solution Approach 2:
Different regions of the electrode have different silver particle size distributions optimized for their specific functions: the lower layer near the substrate has finer particles for adhesion and contact, while the upper layer has coarser particles for mechanical strength and conductivity, creating local optimization throughout the electrode structure
2Manufacturing precision
If the electrode is formed by simply repeating screen-printing and drying of electrode pastes to achieve high aspect ratio, then the electrode structure can be built up, but silver particle contraction during sintering induces breakage
Solution Approach 1:
The patent changes the particle size distribution parameter across different electrode layers. The upper layer uses coarser silver particles (4-8 μm) with higher content that contract less during sintering, providing structural support that prevents breakage, while the lower layer uses finer particles for good contact
Solution Approach 2:
The electrode is constructed as a composite structure with two different silver particle size distributions in different layers. This composite approach combines the advantages of fine particles (good contact) and coarse particles (low contraction, high strength) to achieve both high aspect ratio and reliability
3Manufacturing precision
If multi-layered electrode structure is formed by conventional methods, then high aspect ratio can be achieved, but foaming, cracking, and incomplete combustion of organic binder occur during sintering
Solution Approach 1:
The patent applies preliminary action by carefully selecting organic vehicles with appropriate decomposition temperatures for each layer before sintering. The first electrode layer uses organic vehicle decomposing at 250-400°C, while the upper layer uses organic vehicle decomposing at 150-250°C, preventing premature combustion and foaming during the sintering process
4Reliability
If the conductive paste has high silver content (75-95 wt%) with specific particle size distribution, then the electrode achieves low resistance and high reliability, but the manufacturing precision and particle content control become more difficult
Solution Approach 1:
The patent segments the silver particle content control across different layers. The first electrode layer contains 75-95 wt% silver with 0.5-4 μm particles, while the upper layer contains 75-95 wt% silver with 4-8 μm particles. This segmentation allows each layer to be optimized for its specific function while maintaining overall manufacturing feasibility
Solution Approach 2:
The patent changes the particle size parameter (0.5-4 μm for first layer, 4-8 μm for upper layer) while maintaining high silver content (75-95 wt%). This parameter change enables differentiation between layers for specific functions while keeping the overall silver content high for low resistance, making the high-performance requirement manufacturable
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 approach allows for the formation of high-aspect-ratio electrodes with low resistance and reduced series resistance, enhancing the solar cell's conversion efficiency and reliability while minimizing the risk of breakage and other defects.
Implementation Method 1
The conductive paste is applied by screen-printing or the like, followed by sintering at a high temperature inside of a firing furnace, thereby forming a front surface electrode
Implementation Method 2
there has arisen problem that foaming, cracking, incomplete combustion of an organic binder contained in the conductive paste of a lower layer
Data Source
Figure 1~3
AI summary
The present invention is directed to a semiconductor substrate having an electrode formed thereon, the electrode including at least silver and glass frit, the electrode including: a multi-layered structure constituted of a first electrode layer joined directly to the semiconductor substrate, and an upper electrode layer formed of at least one layer and disposed on the first electrode layer; wherein the upper electrode layer is formed by firing a conductive paste having a total silver content of 75 wt% or more and 95 wt% or less, the content of silver particles having an average particle diameter of 4 µm or greater and 8 µm or smaller with respect to the total silver content in the upper electrode layer being higher than that in the first electrode layer. As a consequence, it is possible to form the electrode, which has the high aspect ratio and hardly suffers an inconvenience such as a break, on the semiconductor substrate by a simple method.