| 研究実績の概要 |
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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| 今後の研究の推進方策 |
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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