MWT Silicon Solar Cell Metallization via Low Fire-Through Paste
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Solution Overview
Problem
The production of MWT silicon solar cells with n-type silicon bases faces challenges in achieving efficient electric contact and adhesion of metallization pastes without damaging the p-type emitter, leading to potential shunting characteristics.
Innovation Solution
A process involving a conductive metal paste with poor fire-through capability, comprising silver, copper, or nickel, along with a p-type dopant and organic vehicle, is applied to the holes of the silicon wafer, fired at 700-900°C to form anodic back contacts, ensuring good ohmic contact and adhesion without damaging the p-type emitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conductive metal paste with good fire-through capability is used to form metallization in holes, then the electric contact is improved, but the p-type emitter is damaged leading to shunting characteristics
Solution Approach 1:
The paste composition is modified by adjusting the metal particle size distribution, glass frit content, and organic vehicle formulation to reduce fire-through capability. This parameter change allows the paste to form adequate electrical contact without penetrating and damaging the underlying p-type emitter layer during the firing process.
Solution Approach 2:
The conductive metal paste is formulated as a composite material containing metal particles (silver, copper, or nickel), glass frit, and organic vehicle in specific proportions. This composite structure provides controlled rheology and firing behavior, enabling the paste to adhere to and conduct electricity through the n-type silicon base while stopping before damaging the p-type emitter.
2Duration of action of stationary object
If the metallization paste is fired at high temperature to improve adhesion, then the service life is improved, but the p-type emitter is damaged
Solution Approach 1:
The firing temperature profile is optimized to balance adhesion and emitter protection. The paste is designed to achieve adequate bonding at temperatures that do not exceed the emitter's thermal tolerance, preventing damage while ensuring long-term durability of the electrical contact.
3Object-affected harmful factors
If the conductive metal paste has poor fire-through capability, then the p-type emitter is protected, but the electric contact and adhesion are insufficient
Solution Approach 1:
The paste formulation is precisely tuned to achieve the optimal fire-through capability - not too strong to damage the emitter, but not too weak to fail establishing electrical contact. This is accomplished by controlling metal particle size, glass frit composition, and organic binder content to create a paste that forms reliable contacts while protecting the underlying p-type emitter.
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
This process enhances the electric efficiency of MWT silicon solar cells by providing a long service life with improved adhesion and reduced risk of shunting, while maintaining the integrity of the p-type emitter.
Implementation Method 1
firing the dried conductive metal paste, whereby the wafer reaches a peak temperature of 700 to 900° C.
Data Source
AI summary
A process for the production of a MWT silicon solar cell comprising the steps:(1) providing an n-type silicon wafer with (i) holes forming vias between the front-side and the back-side of the wafer and (ii) a p-type emitter extending over the entire front-side and the inside of the holes,(2) applying a conductive metal paste to the holes of the silicon wafer to provide at least the inside of the holes with a metallization,(3) drying the applied conductive metal paste, and(4) firing the dried conductive metal paste, whereby the wafer reaches a peak temperature of 700 to 900° C.,wherein the conductive metal paste has no or only poor fire-through capability and comprises (a) at least one particulate electrically conductive metal selected from the group consisting of silver, copper and nickel, (b) at least one particulate p-type dopant, and (c) an organic vehicle.