Heat Diffusion Barrier Assembly for Silicon Melt Thermal Control
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Solution Overview
Problem
Achieving controlled and uniform heat flow within a silicon melt is challenging due to the high thermal conductivity of molten Si and the thermal insulating properties of fused silica crucibles, which limits the stability and thickness of crystalline sheets produced in the horizontal ribbon growth technique for solar cells.
Innovation Solution
An apparatus with a heat diffusion barrier assembly is used within the crucible to create an isolation region with higher heat flow density at the melt surface, while maintaining a lower thermal conductivity than molten silicon, allowing for tailored heat distribution and increased heat flow density at the surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fused silica crucible is used to contain silicon melt, then the crucible resists reaction with silicon at elevated temperature, but the thermal insulating properties of fused silica limit the heat flow to the melt surface
Solution Approach 1:
The crucible is segmented into two distinct parts: an inner crucible made of fused silica that contacts the silicon melt and provides chemical resistance, and an outer crucible made of a material with higher thermal conductivity that enables efficient heat transfer to the melt. This segmentation allows each material to perform its optimal function without compromise.
Solution Approach 2:
A heat diffusion barrier assembly is introduced as an intermediary component between the outer crucible and the inner crucible/melt system. This assembly controls and optimizes the heat flow path, allowing thermal energy to pass from the outer crucible through to the melt while maintaining the chemical resistance provided by the fused silica inner crucible.
2Use of energy by moving object
If heat is introduced at the bottom of the crucible, then heat flows through the melt, but the high thermal conductivity of molten Si causes heat to spread out before reaching the melt surface
Solution Approach 1:
The heat diffusion barrier assembly creates localized heat flow paths that concentrate thermal energy toward specific regions of the melt surface. By strategically positioning and designing the barrier geometry, heat is directed to where it is most needed for crystallization while preventing excessive spreading that would reduce manufacturing precision.
Solution Approach 2:
The heat diffusion barrier assembly introduces a new spatial dimension for heat flow control within the crucible. By placing the barrier at a specific depth and orientation, it creates a three-dimensional heat flow pattern that concentrates energy vertically toward the surface rather than allowing lateral spreading, effectively adding a control dimension to the thermal field.
3Use of energy by moving object
If the outer temperature of the fused silica crucible is maintained at high temperature to increase heat flow, then more heat reaches the melt, but the fused silica softens above 1880 K
Solution Approach 1:
The crucible structure is segmented into an inner fused silica crucible that remains at lower temperature and maintains structural stability, and an outer crucible that can be maintained at higher temperature to provide the necessary heat flow. The segmentation allows the outer crucible to bear the thermal load while the inner crucible maintains chemical resistance and structural integrity.
Solution Approach 2:
The heat diffusion barrier assembly acts as a thermal mediator that decouples the temperature requirements of the outer and inner crucible components. It allows the outer crucible to operate at high temperature for efficient heat generation while controlling the heat transfer rate to prevent the inner fused silica crucible from reaching its softening point.
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 solution enables stable and uniform heat flow to the melt surface, facilitating the growth of crystalline sheets with controlled thickness and stability, overcoming the limitations of conventional apparatus by concentrating or uniforming heat flow as needed.
Implementation Method 1
heat diffusion barrier assembly comprising at least one heat diffusion barrier disposed within the crucible and defining an isolation region in the melt
Implementation Method 2
fused silica is a good thermal insulator such that a large thermal gradient is required to conduct substantial heat to the silicon melt
Implementation Method 3
a heater disposed below a first side of the crucible and configured to supply heat through the melt to the exposed surface
Data Source
AI summary
An apparatus for controlling heat flow within a melt. The apparatus may include a crucible configured to contain the melt where the melt has an exposed surface. The apparatus may also include a heater disposed below a first side of the crucible and configured to supply heat through the melt to the exposed surface, and a heat diffusion barrier assembly comprising at least one heat diffusion barrier disposed within the crucible and defining an isolation region in the melt and an outer region in the melt.