Multimetal Semiconductor Alloy Metallization for Solar Cells
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Solution Overview
Problem
Current solar cell manufacturing techniques face challenges with high contact resistance, copper diffusion issues, and non-uniform metal silicide layers, leading to performance degradation and reduced lifetime, especially in silicon-based solar cells with varying substrate properties.
Innovation Solution
A multimetal semiconductor alloy layer is formed on the front side surface of a semiconductor substrate, comprising a first elemental metal that alloys with the semiconductor at a specific temperature and a second elemental metal that does not, along with an optional metal diffusion barrier layer and a copper-containing layer, to improve uniformity and longevity of the solar cell.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If screen printed metal pastes are used for metallization, then high throughput and simplicity in processing are achieved, but high contact resistance and shadowing from wide conductive lines occur
Solution Approach 1:
The patent replaces the mechanical screen printing process with an electroplating process. Instead of using screen printing screens and paste materials, the invention uses electrochemical deposition to form metal layers and metal semiconductor alloy layers on the solar cell surface, thereby eliminating the inherent limitations of screen printing while maintaining high throughput capability
Solution Approach 2:
The patent changes the metallization method from mechanical screen printing to electrochemical plating, and further changes the material state from paste to metal semiconductor alloy. This parameter change enables better control over layer thickness, composition, and electrical properties, resolving the contradiction between throughput and contact resistance
2Reliability
If plated copper is used for metallization, then contact resistance is improved, but copper diffusion into the silicon solar cell occurs and damages performance
Solution Approach 1:
The patent creates a composite metallization structure consisting of multiple layers: a metal semiconductor alloy layer (containing copper and silicon), an intermediate metal layer, and a protective coating. This composite structure allows copper to be present in controlled amounts within the alloy layer while preventing harmful diffusion into the bulk silicon, thereby maintaining low contact resistance without performance degradation
Solution Approach 2:
The metal semiconductor alloy layer acts as an intermediary between the copper-containing plated layer and the silicon substrate. By forming this intermediate alloy layer, the patent prevents direct contact between pure copper and silicon, thereby blocking copper diffusion while maintaining electrical conductivity
3Object-generated harmful factors
If thick nickel silicide layers are formed to prevent copper diffusion, then diffusion protection is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent changes the approach from forming thick nickel silicide barriers to controlling the composition and thickness of the metal semiconductor alloy layer itself. By adjusting plating parameters, alloy composition, and thermal treatment conditions, the invention achieves effective copper diffusion prevention with much thinner layers, thereby reducing manufacturing complexity
4Reliability
If vacuum based metallization processes are used, then metallization quality is improved, but cost increases and throughput decreases
Solution Approach 1:
The patent replaces vacuum-based physical vapor deposition processes with electrochemical plating. This substitution maintains high metallization quality through precise control of layer composition and structure while enabling aqueous-based processing that is inherently more suitable for high-volume, cost-effective manufacturing
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 multimetal semiconductor alloy layer enhances the uniformity and control of metal semiconductor alloy thickness, leading to improved solar cell performance and extended lifetime by preventing copper diffusion and maintaining performance even at elevated temperatures.
Implementation Method 1
a first elemental metal that forms an alloy with a semiconductor material at a first anneal temperature
Implementation Method 2
The anneal includes a furnace anneal, a rapid thermal anneal, a spike anneal, a microwave anneal or a laser anneal
Implementation Method 3
a second elemental metal that differs from the first elemental metal and that does not form an alloy with a semiconductor material at the first anneal temperature
Data Source
AI summary
A photovoltaic device, such as a solar cell, having improved performance is provided. In one embodiment, the photovoltaic device includes a multimetal semiconductor alloy layer located on exposed portions of a front side surface of a semiconductor substrate. The multimetal semiconductor alloy layer includes at least a first elemental metal that forms an alloy with a semiconductor material, and a second elemental metal that differs from the first elemental metal and that does not form an alloy with a semiconductor material at the same temperature as the first elemental metal. The photovoltaic device further includes a copper-containing layer located atop the multimetal semiconductor alloy layer.