All-Aluminum Back Surface Field Paste for Silicon Solar Cells
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Solution Overview
Problem
Conventional crystalline silicon solar cells face issues with photovoltaic conversion efficiency due to metal defects in silver electrodes and poor adhesion of aluminum back surface fields, leading to electrical leakage and increased costs.
Innovation Solution
An all-aluminum back surface field aluminum paste comprising 60-70% spherical aluminum powder, 5-10% nanometer metal oily solution, 1-10% inorganic binder, 10-20% organic binder, and 1-5% accessory ingredient, which improves adhesion with silver paste and reduces bulk phase resistance, preventing oxidation and enhancing ohmic contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silver electrode is used in conventional solar cell structure, then good electrical conductivity is achieved, but metal defects form in silicon wafer causing electric leakage and reduced photovoltaic conversion efficiency
Solution Approach 1:
The invention extracts and removes the harmful silver material from the back electrode structure, replacing it entirely with aluminum-based materials. This eliminates the source of metal defects and electric leakage while maintaining the electrical conductivity function through the aluminum back surface field and aluminum paste electrode.
Solution Approach 2:
The invention changes the material composition parameter from silver-containing paste to pure aluminum-based paste, and modifies the processing temperature parameter by using lower sintering temperatures (700-850℃) compared to conventional silver paste processes, thereby preventing metal defects while achieving good electrical contact.
2Reliability
If aluminum back surface field is added to cover back electrode edge, then edge coverage is improved, but width of back electrode increases and cost increases
Solution Approach 1:
The invention merges the back electrode and aluminum back surface field into a single integrated aluminum-based structure. The aluminum paste serves dual functions as both the back electrode material and the back surface field material, eliminating the need for separate silver paste and aluminum back surface field materials, thereby reducing material quantity and cost.
Solution Approach 2:
The aluminum-based paste performs multiple functions simultaneously: it acts as the back electrode providing electrical contact, forms the aluminum back surface field for edge coverage and ohmic contact, and eliminates the need for separate silver paste and aluminum back surface field layers, achieving cost reduction while maintaining reliability.
3Reliability
If conventional silver aluminum paste is used for back electrode, then good electrical conductivity is achieved, but adhesion with aluminum back surface field is poor and cost is high
Solution Approach 1:
The invention uses homogeneous aluminum-based materials for both the back electrode paste and the aluminum back surface field, ensuring compatible thermal expansion coefficients and chemical properties. This homogeneity improves interfacial adhesion strength while maintaining good electrical conductivity, eliminating the adhesion problems associated with silver-aluminum interfaces.
Solution Approach 2:
The invention employs a composite aluminum-based paste system containing aluminum powder, organic binders, and inorganic binders, which provides both excellent electrical conductivity and strong adhesion to the aluminum back surface field. The composite formulation ensures compatible thermal and mechanical properties at the interface, achieving both conductivity and strength requirements.
4Reliability
If high temperature sintering is used for silver aluminum paste, then good electrical contact is achieved, but sintering depth exceeds aluminum diffusion depth affecting P-N junction quality
Solution Approach 1:
The invention optimizes the sintering temperature parameter to a lower range (700-850℃) compared to conventional silver paste processes. This temperature parameter change is sufficient to achieve good electrical contact and aluminum diffusion into the silicon substrate without exceeding the depth that would damage the P-N junction, thereby maintaining both electrical contact quality and junction integrity.
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 all-aluminum back surface field aluminum paste increases photovoltaic conversion efficiency and reduces manufacturing costs by improving adhesion and electrical conductivity, preventing metal defects and oxidation, and ensuring stable ohmic contact.
Implementation Method 1
improves adhesion with silver paste and reduces bulk phase resistance, preventing oxidation and enhancing ohmic contact
Implementation Method 2
A potential difference on a P-N junction makes a hole and an electron move through the junction in an opposite direction, thus leading to the flow of current
Implementation Method 3
The paste is mainly added with a low melting cladding base metal... the silver powder is enabled to form a good sintering interlay with the aluminum back surface field
Data Source
AI summary
The invention discloses an all-aluminum back surface field aluminum paste for a crystalline silicon solar cell and a preparation method thereof. The all-aluminum back surface field paste mainly comprises 60-70% aluminum powder, 5-10% nanometer metal oily solution, 1-10% inorganic binder, 10-20% organic binder, 5-30% organic solvent and 1-5% accessory ingredient. According to the aluminum paste prepared by the present invention, the back surface preparing process of an all-aluminum back surface field can be implemented preferably; moreover, the paste has great adhesive force, is easy to be better adhered to silver paste printed afterwards; meanwhile, the paste can be in good contact with a silicon chip through the nanometer metal oily solution added into the paste, the aluminum back surface is prevented from falling off, and good ohm contact can be formed, so that the photoelectric conversion efficiency is increased, and the economic benefits of enterprises are increased.