Silicon Sheet Separation via Buoyancy and Elasticity
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Solution Overview
Problem
Current methods for producing silicon sheets from a melt, such as sawing or pulling silicon ribbons, result in material waste, increased costs, and poor crystal quality due to kerf losses, squaring inefficiencies, and temperature gradients, which limit the production of thinner, higher-efficiency solar cells.
Innovation Solution
A method utilizing the elasticity and buoyancy of the sheet to separate it from the melt surface, allowing it to float and be pulled horizontally, thereby avoiding stress and complex angle control, and optimizing crystal growth independently of meniscus stabilization, which reduces material waste and improves crystal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If silicon sheets are pulled vertically from a melt, then production speed can be increased, but temperature gradients cause stress and poor crystal quality
Solution Approach 1:
The patent transitions from vertical ribbon pulling to horizontal sheet growth, changing the growth dimension from vertical to horizontal. This allows the sheet to grow laterally across the melt surface rather than being pulled upward, eliminating the temperature gradient problem while maintaining high production speed through rapid lateral solidification.
Solution Approach 2:
The patent uses a floating mechanism where the solidifying sheet buoyantly floats on the melt surface, counteracting gravitational forces that would otherwise create stress during vertical pulling. This floating support eliminates the need for rapid cooling and reduces thermal stress, improving crystal quality while maintaining productivity.
2Ease of manufacture
If silicon sheets are sawed from ingots, then existing manufacturing processes can be used, but kerf loss and material waste increase costs
Solution Approach 1:
The patent utilizes the phase transition of silicon from liquid to solid at the melt surface to directly form sheets, eliminating the need for subsequent sawing operations. The sheet solidifies in its final form directly from the melt, converting a two-step process (ingot growth + sawing) into a single-step direct sheet formation process that eliminates kerf loss.
Solution Approach 2:
The patent extracts and eliminates the problematic sawing step from the manufacturing process by directly forming sheets from the melt. This removes the source of kerf loss and material waste while simplifying the overall manufacturing process, reducing both material waste and production complexity.
3Reliability
If the sheet is pulled at a low angle to prevent melt spilling, then crystal quality improves, but the apparatus complexity and angle control difficulty increase
Solution Approach 1:
The patent creates an equipotential floating interface where the sheet buoyantly floats on the melt surface at a constant level. This eliminates the need for complex angle control mechanisms, as the sheet naturally maintains a horizontal position through buoyancy forces, simplifying the apparatus while ensuring consistent crystal quality.
Solution Approach 2:
The floating mechanism is self-regulating, automatically maintaining the optimal horizontal growth position through buoyancy forces without requiring external angle control systems. The sheet self-adjusts to the correct orientation, eliminating the need for complex control apparatus and reducing system complexity while maintaining high crystal quality.
4Reliability
If the sheet thickness is reduced to produce thinner solar cells, then efficiency improves, but the percent of silicon waste per cut increases
Solution Approach 1:
The patent uses direct solidification from the melt to form thin sheets without subsequent cutting, eliminating kerf loss entirely. The phase transition from liquid to solid occurs at the desired thin thickness, allowing production of ultra-thin sheets (potentially micrometer-scale) without the material waste associated with sawing thicker ingots.
Solution Approach 2:
The patent changes the fundamental growth parameter from thick ingot formation followed by cutting to direct thin sheet solidification. By controlling the solidification process to produce sheets at the target thickness directly, the method eliminates the need for cutting and associated waste, enabling efficient production of thin solar cells with minimal material loss.
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 approach reduces material waste, lowers production costs, and enhances crystal quality by minimizing stress and dislocations, enabling the production of thinner, more efficient silicon sheets without the need for complex apparatus or angle adjustments.
Implementation Method 1
utilizing the elasticity and buoyancy of the sheet to separate it from the melt surface, allowing it to float and be pulled horizontally
Implementation Method 2
utilizing the elasticity and buoyancy of the sheet to separate it from the melt surface, allowing it to float and be pulled horizontally
Implementation Method 3
A sheet is formed on the melt in a second region
Implementation Method 4
The removed latent heat during cooling and solidifying of the silicon must be removed along the vertical ribbon. This results in a large temperature gradient along the ribbon
Data Source
AI summary
Embodiments related to sheet production are disclosed. A melt of a material is cooled to form a sheet of the material on the melt. The sheet is formed in a first region at a first sheet height. The sheet is translated to a second region such that it has a second sheet height higher than the first sheet height. The sheet is then separated from the melt. A seed wafer may be used to form the sheet.