2021 Fiscal Year Research-status Report
Development of a method to form hollow silicon spheres, with application to photovoltaic cells: experiment and computation.
| Project/Area Number |
20K04293
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| Research Institution | Ritsumeikan University |
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Principal Investigator |
WELLS John・C 立命館大学, 理工学部, 教授 (60301644)
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| Co-Investigator(Kenkyū-buntansha) |
河野 悠 立命館大学, 理工学部, 助教 (40822838)
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| Project Period (FY) |
2020-04-01 – 2023-03-31
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| Keywords | Hollow / silicon / millisphere / solidification / horn |
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| Outline of Annual Research Achievements |
Hollow silicon millispheres have been fabricated using a hollow coaxial jet for the first time. Silicon was melted in a graphite crucible at 1823 K, then ejected from the annulus of a coaxial nozzle as argon gas was injected from an inner nozzle. Diameters were 1 - 2 mm with spherical outer surfaces, and the frequency of formation was approximately 145 Hz. The silicon was in polycrystalline form. Wall thickness increased from one side of the sphere to the other.
The interior surfaces were somewhat non-spherical, with inward horn-like structures that tended to occur inside the thicker region of the wall. Such horn structures are known to form during the final stage of solidification of materials that expand upon freezing. However they have not previously been observed on a concave substrate.
The silicon contained carbon impurity whose concentration was greater in the bulk, and at the tips of the horn structure. This observation provides further evidence that solidification finished at the horn structures.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
A year ago, progress was somewhat delayed because the postdoctoral fellow Dr. BHAGAT was unable to enter Japan on schedule. Progress has accelerated with his arrival. Concretely, he has successfully executed an experiment that proved it possible to form hollow silicon spheres, thereby fulfilling an important objective of this project.
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| Strategy for Future Research Activity |
We will improve the experimental procedures and apparatus to achieve more precise positioning of the inner nozzle, and thence better reproducibility. We will also aim to reduce carbon impurity by changing the materials employed. Numerical simulations will be pursued to permit design of a stronger inner nozzle that still forms hollow spheres with sufficiently thin walls.
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| Causes of Carryover |
We were able to produce of hollow silicon spheres mostly by using materials and components from previous experiments. For the next step, various newly fabricated parts will be employed, notably an alumina crucible.
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