Triple Pass Cascade Silicon Purification Process
Solution Overview
Problem
Current methods for purifying silicon to solar grade from metallurgical grade are inefficient, leading to excessive impurities and uneven boron and phosphorus concentrations, which affect the quality and yield of solar cells.
Innovation Solution
A triple pass cascade process using a metallic solvent, such as aluminum, where silicon is repeatedly contacted with mother liquors and solvent metals to achieve consistent and lower impurity levels, allowing for the production of high-quality silicon with boron levels less than 0.7 ppmw and phosphorus levels less than boron, thereby reducing material waste and increasing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional silicon purification processes are used, then production cost is reduced, but impurity levels remain high and inconsistent
Solution Approach 1:
The purification process is divided into multiple sequential passes (first pass, second pass, third pass) where silicon is progressively purified through repeated fractional crystallization. Each pass removes additional impurities, with the third pass achieving the lowest impurity levels including phosphorus less than boron concentration
Solution Approach 2:
The process maintains continuous purification action through multiple sequential crystallization cycles. Mother liquor from each pass is reused in subsequent passes, ensuring continuous removal of impurities while maximizing silicon recovery and minimizing material waste
2Manufacturing precision
If single pass purification is used, then production time is reduced, but phosphorus levels exceed boron levels
Solution Approach 1:
The purification is segmented into three distinct passes, each targeting specific impurity removal. The first pass removes initial impurities, the second pass further purifies, and the third pass achieves the critical phosphorus less than boron concentration ratio required for solar-grade silicon
Solution Approach 2:
The process changes concentration parameters through sequential passes, transforming the phosphorus-to-boron ratio from excess phosphorus in single-pass purification to the desired phosphorus-less-than-boron concentration in triple-pass purification
3Manufacturing precision
If directional solidification of UMG silicon is used, then ingot production is achieved, but phosphorus concentration increases at the top
Solution Approach 1:
The triple-pass purification is performed as a preliminary action before directional solidification. This pre-purification ensures uniform low phosphorus levels throughout the silicon material, preventing the phosphorus concentration gradient that would otherwise form during subsequent directional solidification
Solution Approach 2:
The triple-pass fractional crystallization process acts as an intermediary purification step between metallurgical grade silicon and the final directional solidification process, removing impurities before the ingot formation stage
4Manufacturing precision
If repeated fractional crystallization is used, then impurity levels decrease, but silicon loss in by-products increases
Solution Approach 1:
The process discards impurity-rich mother liquor from each pass while recovering and reusing it in subsequent passes. This maximizes silicon extraction from each batch while ensuring impurities are progressively removed, achieving high purity with minimal silicon loss
Solution Approach 2:
Mother liquor containing dissolved silicon is continuously reused across multiple passes rather than being discarded. This continuous utilization ensures maximum silicon recovery while maintaining progressive purification, reducing overall silicon loss in by-products
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 process results in purified silicon with consistent impurity levels, reducing material waste and enabling the production of higher efficiency solar cells by minimizing phosphorus compensation and optimizing P/N junction formation.
Implementation Method 1
contacting a first silicon with a second mother liquor to form a first mixture. The first mixture is melted to form a first molten mixture
Implementation Method 2
The first molten mixture is cooled to form first silicon crystals and a third mother liquor
Implementation Method 3
cooling the first molten mixture. The cooling of the first molten mixture forms first silicon crystals and a third mother liquor
Data Source
AI summary
The present invention relates to a method of purifying a material using a metallic solvent. The present invention includes a method of purifying silicon utilizing a cascade process. In a cascade process, as the silicon moves through the purification process, it contacts increasingly pure solvent metal that is moving through the process in an opposite direction.