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Si nano-particle solar cells

Figure 1   Theoretical energy conversion efficiency of solar cells composed of Si nano-particles.

   The Si band-gap increases as the diameter of Si nano-particles decreases to nano-meter size.  For example, the band-gap of Si nano-particles with 2.4 nm diameter is 2.2 eV, which is about twice that of crystalline Si.  Therefore, the energy conversion efficiency of Si solar cells can be increased by use of Si nano-particles with various band-gap energies.  The theoretical conversion efficiency of solar cells with 2.2 eV band-gap Si nano-particles/1.7 eV band-gap Si nano-particles/1.1 band-gap Si/0.85 band-gap FeSi particles structure is 60 %, which is about twice that of crystalline Si solar cells (cf. Figure 1).

   Previous production methods of Si nano-particles such as a CVD method require expensive apparatuses, and are time-consuming, resulting in high fabrication cost.  Therefore, the previous production methods are difficult to apply to solar cell fabrication.  In Kobayashi laboratory, we have developed a method of Si nano-particle fabrication by use of mechanical powdering and chemical dissolution methods which are applicable to mass-production.