2014 Fiscal Year Annual Research Report
| Project/Area Number |
13F03716
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| Research Institution | National Institute of Advanced Industrial Science and Technology |
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Principal Investigator |
SVRCEK Vladimir 独立行政法人産業技術総合研究所, エネルギー・環境領域 太陽光発電工学研究センター, 主任研究員 (80462828)
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| Co-Investigator(Kenkyū-buntansha) |
LOZAC'H Mickael 独立行政法人産業技術総合研究所, エネルギー・環境領域 太陽光発電研究センター, 外国人特別研究員
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| Project Period (FY) |
2013-04-01 – 2016-03-31
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| Keywords | nanocrystals |
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| Outline of Annual Research Achievements |
Alloyed silicon-tin nanocrystals (SiSn-ncs) have been successfully fabricated to satisfy two challenging points for the development of future solar cell devices: a material with an energy band gap lower than the one of silicon, and a direct bandgap material that increases greatly the absorption of the solar spectrum.
SiSn-ncs were fabricated by laser ablation in liquid media technique that generates high localized plasma on the surface of amorphous SiSn target. This method synthetized SiSn-ncs alloys that was not possible using conventional techniques such as thin film deposition, high frequency plasma enhanced chemical vapor deposition, or pulsed laser deposition. The nanoparticles generated reach a quantum confinement size about 4nm with clear atomic plans observed by transmission electron microscopy. SiSn-ncs were analyzed by synchrotron radiation XRD to estimate a Si0.88Sn0.12-ncs alloys that can correspond theoretically to direct energy gap transition. Optical bandgap was estimated to be 0.81eV by absorbance measurements, which is well below the silicon bandgap. A low concentration of oxygen on the surface of SiSn-ncs was underlined by Fourier transient infrared spectra, which is of great importance for the stability over time of the devices.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
The photovoltaic properties of SiSn-ncs were also analyzed using hybrid solar cell devices. Our findings underlines an improvement of the short-circuit current for devices using conjugated polymer PTB7 mixed with SiSn-ncs as active layer. This improvement is related to a better absorption at longer wavelengths due to the low energy band gap and also due to its possible direct transition. An improvement of the open-circuit voltage is also confirmed, related to the bulk heterojunction quality. It is the first report about the photovoltaic effect of SiSn-ncs alloy.
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| Strategy for Future Research Activity |
The main future project will focus on the realization of SiSn-ncs solar cell structures as active layer with higher concentration of Sn. For this the atomic layer deposition (ALD) is a promising technique to reach higher Sn concentration and further decrease the material bandgap. Another important parameter is the strain, and especially the tensile strain, to engineer and control the indirect to direct bandgap transition, which remains challenging to demonstrate experimentally. These research plans will be also guide by rigorous analysis of the band structure to underline the conduction and valance band position related to the direct energy gap transition, which will provide key points for the physical knowledge of this alloy. Beside, in a near future, the understanding of the optimal laser condition for the synthesis of SiSn-ncs can provide information about the relation between the energy needed for the formation, the constitution and the quantum confinement size of the SiSn-ncs alloy. According to this research plan, solar cells with SiSn-ncs as active layer will be fabricated to underline the photovoltaic properties of SiSn-ncs alloy.
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