| 研究課題/領域番号 |
15K17984
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| 研究機関 | 東京大学 |
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研究代表者 |
項 栄 東京大学, 工学(系)研究科(研究院), 助教 (20740096)
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| 研究期間 (年度) |
2015-04-01 – 2017-03-31
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| キーワード | carbon nanotube / Band gap engineering / TEM / solar cell |
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| 研究実績の概要 |
Single-walled carbon nanotube (SWNT) has recently risen to be a promising candidate material for various solar cells. However, reducing SWNT diameter to meet the band gap requirement for solar energy harvesting remains as a big challenge. We proposed in this project to synthesize high-quality small diameter SWNTs using new combination of catalyst, to investigate the role of new component by transmission electron microscope, and to apply small diameter SWNTs in Si heterojunction solar cells. This year, we focused on the synthesis of small-diameter SWNTs using new bimetallic catalyst, and the investigation of the underlying mechanism.
We found vertically aligned VA-SWNTs with subnanometer diameters can be synthesized by alcohol CVD using a new combination of Co and Cu as bimetallic catalysts. The diameter of VA-SWNTs are uniformly below 1 nm at a CVD temperature of 800 °C, and can be reduced to 0.75 nm at 650 °C with the G/D ratio maintained above 24. This diameter range is confirmed by Raman spectroscopy, optical absorption and transmission electron microscope (TEM).
Scanning transmission electron microscopy energy-dispersive X-ray spectroscopy (EDS-STEM) and high angle annular dark field (HAADF-STEM) imaging are used to clarify the structure of this new Co-Cu catalyst. The results showed that Co catalysts were captured and anchored by adjacent Cu nanoparticles, and thus were prevented from coalescing into a larger size.
The subnanometer-diameter and high-quality SWNTs obtained here are expected to be a candidate for nextgeneration photovoltaic devices.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
The research plan in 2015 was 1) synthesis of diameter-reduced SWNTs using new bimetallic catalyst and 2)investigation of SWNT formation mechanism using transmission electron microscope (TEM).
For the first aspect, we successfully obtained vertically aligned SWNTs from the new combination Co-Cu, and confirmed all SWNTs are below 1 nm in diameter. This is so far as we know the smallest vertically aligned SWNT forest ever reported. We also prepared Co-W catalyst using sputtering and observed enrichment in SWNT chirality. More analysis of the sample and the catalyst struture is in progressing.
For the second aspect, atomic resolution image of Co-Cu catalyst is obtained directly on SiO2 film, which clearly revealed that the anchoring effect of Cu is responsible for the formation of smaller diameter SWNTs comparing to the case when Cu is absent. The results also suggest the potential of applying this in-plane TEM technique to other system.
Therefore, we believe the project is progressing rather smoothly as planed.
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| 今後の研究の推進方策 |
The research plan for 2016 will be as follows.
1) More detailed study on Co-W bimetallic system. We recently observed chirality enrichment for SWNTs grown from sputtered Co-W , so systematic change of the recipe (ratio of Co and W, CVD time, etc.) will be performed to optimize this process. Raman spectroscopy and optical absorption will be used to quantify the chirality distribution in the sample. Furthermore, the structure of Co-W catalyst will be investigated by TEM, particularly for catalyst prepared at different temperatures. Selective area electron diffraction together with high resolution image will be used to confirm the catalyst structure.
2) Constructing Si-SWNT solar cell using small diameter SWNTs. Small diameter SWNTs synthesized from new bimetallic catalyst will be transfered or deposited onto N-type Si. Particularly, a detailed comparison between regular large diameter SWNTs and small diameter SWNTs will be performed and the contribution of small diameter SWNTs on electron-hole generation will be quantified. J-V curve will be measured by a semiconductor analyzer under the illumination of 1.5 AM. Experimental results will be fitted by a p-n diode equation model.
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