Silicon Ingot Grain Boundary Control via Seed Asymmetry
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Solution Overview
Problem
Current methods for producing multicrystalline silicon ingots result in a high density of dislocations and inhomogeneous crystalline orientations, making it difficult to achieve monocrystalline-like ingots with symmetrical grain boundaries, which are essential for high-efficiency photovoltaic cells.
Innovation Solution
A process involving a crucible with a tiling of monocrystalline silicon seeds of different crystalline orientations, positioned alternately and symmetrically, allowing directional solidification to control the propagation of grain boundaries, ensuring symmetrical grain boundaries in the ingot and subsequent wafers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If directional solidification with multiple monocrystalline seeds is used to produce mono-like silicon ingots, then the crystalline structure is improved, but seed boundaries create grain boundaries and dislocations that reduce photovoltaic characteristics
Solution Approach 1:
The patent applies asymmetry by using seeds with different crystalline orientations (e.g., <100> and <110> orientations) arranged in an asymmetric pattern. This asymmetric arrangement causes grain boundaries to propagate vertically along the solidification direction rather than horizontally, preventing them from intersecting the wafer cutting planes and eliminating their harmful effects on photovoltaic characteristics
Solution Approach 2:
The patent applies local quality by creating different crystalline orientations in different regions of the ingot. Seeds with specific orientations are placed in specific locations to control the local grain boundary propagation, ensuring that grain boundaries form in regions that will be removed during ingot cutting rather than in the final wafer regions
2Productivity
If conventional directional solidification is used to produce multicrystalline silicon ingots, then large volumes of silicon can be crystallized, but the ingots have high density of dislocations and inhomogeneous crystalline orientations
Solution Approach 1:
The patent applies parameter changes by systematically varying the crystalline orientation parameters of the seeds used in directional solidification. By changing the orientation angles and types of seeds (e.g., using <100>, <110>, or other orientations), the patent controls the nucleation and growth of crystals to achieve uniform crystalline orientation throughout the ingot while maintaining large crystallization volumes
Solution Approach 2:
The patent applies preliminary action by pre-positioning monocrystalline seeds with controlled orientations at the bottom of the crucible before solidification begins. This preliminary arrangement of seeds with specific orientations guides the entire subsequent solidification process, ensuring uniform crystalline structure throughout the ingot without requiring complex control during the actual crystallization
3Quantity of substance
If seeds are positioned next to each other in the bottom of the crucible, then industrial crucible sizes can be achieved, but numerous seed boundaries are created that propagate as grain boundaries
Solution Approach 1:
The patent uses asymmetric arrangement of seeds with different orientations to control grain boundary propagation. By strategically positioning seeds with specific orientations in an asymmetric pattern, grain boundaries are directed to propagate vertically along the solidification direction, allowing them to be eliminated through subsequent ingot cutting while maintaining large ingot sizes
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 process enables the production of silicon ingots and wafers with controlled grain boundaries, eliminating defects and enhancing photovoltaic characteristics such as current, voltage, and efficiency by producing wafers free of grain boundaries.
Implementation Method 1
carrying out the directional solidification of silicon by seeded regrowth in a growth direction collinear to the axis (Z)
Data Source
AI summary
A method for producing a silicon ingot, provided with symmetrical grain boundaries, including at least steps made of: (i) providing crucible with longitudinal axis, bottom of which includes a paving formed from monocrystalline cuboid silicon seeds with a square or rectangular base and arranged contiguously, the paving, when viewed according to axis, being in shape of a grid of orthogonal directions (x) and (y) parallel to edges of seeds; and (ii) proceeding with controlled solidification of silicon by growth on seeds in a growth direction collinear to axis; wherein paving in step (i) is produced from identical silicon seeds, with two seeds contiguous in direction (x) being images of each other by turning axis (y) and two seeds contiguous in direction (y) being images of each other by turning axis (x), and misorientation 2θ between crystalline arrays of two contiguous seeds being greater than 4°.