Silicon ingot seed crystal arrangement for defect reduction
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Solution Overview
Problem
The challenge in improving the conversion efficiency of solar cells lies in reducing defects in silicon ingots and blocks, which are often caused by the mono-like casting method's limitations, such as distortions and defects at the mold's side walls and the adjacent seed crystals, leading to quality degradation.
Innovation Solution
A method involving a manufacturing apparatus that uses a seed crystal arrangement with coincidence boundaries to promote unidirectional solidification, reducing defects by forming functional grain boundaries and relaxing distortions, thereby improving the quality of silicon ingots, blocks, and substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the mono-like casting method is used to grow crystal grains upward from a seed crystal, then pseudo single crystal silicon with improved crystal orientation is obtained, but distortions and defects occur at the mold side walls and adjacent seed crystals
Solution Approach 1:
The mold is divided into multiple regions with different cooling conditions: a first region with high cooling efficiency (near cooling holes) and a second region with low cooling efficiency (away from cooling holes). This segmentation allows different parts of the silicon ingot to solidify at different rates, preventing uniform distortion and defects while maintaining overall crystal orientation quality.
Solution Approach 2:
Different regions of the mold are assigned different thermal properties through selective placement of cooling holes. The first region has enhanced cooling capability to promote controlled solidification, while the second region has reduced cooling to minimize thermal stress and distortion. This local differentiation of quality resolves the contradiction between achieving good crystal orientation and avoiding defects.
2Productivity
If multiple seed crystals are arranged on the bottom surface of the mold, then productivity is improved, but defects increase at the boundaries between seed crystals
Solution Approach 1:
An intermediate seed crystal is introduced between adjacent first and second seed crystals. This intermediate seed crystal acts as a mediator that prevents direct interaction and potential defect formation at the boundaries of the first and second seed crystals. The intermediate seed crystal buffers the thermal and structural stress, maintaining quality uniformity while allowing multiple seed crystals to be used for improved productivity.
3Ease of manufacture
If uniform cooling is applied across the entire mold, then solidification is simplified, but distortions and defects occur due to thermal stress
Solution Approach 1:
The cooling system is segmented into multiple zones with different cooling intensities. Cooling holes are strategically positioned to create a first region with high cooling efficiency and a second region with low cooling efficiency. This segmentation maintains relative process simplicity while preventing thermal stress and defects that would occur with uniform cooling.
Solution Approach 2:
The cooling parameter (heat transfer efficiency) is changed spatially across different regions of the mold. By adjusting the density and positioning of cooling holes, the cooling rate varies from region to region, optimizing solidification conditions and preventing thermal stress-induced defects while maintaining manageable process complexity.
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 enhances the quality of silicon ingots, blocks, and substrates by reducing defects and improving crystal orientation, leading to higher conversion efficiency and productivity in solar cell production.
Implementation Method 1
causing the silicon melt to perform unidirectional solidification upward from the bottom surface portion side of the mold
Implementation Method 2
using a silicon melt to grow crystal grains upward starting from a seed crystal arranged on the bottom surface portion of the mold makes it possible to form a pseudo single crystal
Implementation Method 3
Each of a boundary between the first pseudo single crystal region and the first intermediate region and a boundary between the second pseudo single crystal region and the first intermediate region includes a coincidence boundary
Data Source
AI summary
An ingot includes a first surface, a second surface opposite to the first surface, and a third surface positioned along a first direction and connecting the first surface and the second surface. The ingot includes: a first pseudo single crystal region; an intermediate region containing one or more pseudo single crystal regions; and a second pseudo single crystal region. The first pseudo single crystal region, the intermediate region, and the second pseudo single crystal region are positioned adjacent sequentially in a second direction perpendicular to the first direction. In the second direction, a width of each of the first and second pseudo single crystal regions is larger than a width of the first intermediate region. Each of a boundary between the first pseudo single crystal region and the intermediate region and a boundary between the second pseudo single crystal region and the intermediate region includes a coincidence boundary.