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In this paper, we introduce research and development in SSPS (aimed at global energy supply) in Japan. To build SSPS, we must develop ultra lightweight materials and high efficiency energy conversion materials. Feasibility of adapting FGM concept for those new demands and advanced research theme for future FGM research are also introduced in this paper.

As part of research and development into the Laser Based Space Solar Power System (L-SSPS), a laser-photovoltaic power converter for 1.07 /lm laser light has been researched at the Japan Aerospace Exploration Agency (JAXA). To improve conversion efficiency of the InGaAs laser-photovoltaic power converter, photovoltaic properties under 1.07 /lm laser illumination were calculated in this study with varying the structural parameters such as InIGa ratio, layer thickness, p/n junction depth and carrier concentration of the InGaAs cell. The conversion efficiency of 42.6 % at 0.3 W/cm 2 laser irradiance and 300 K cell temperature was obtained by optimizing all the structural parameters, indication that the thickness and carrier concentration optimization leads remarkable improvements in conversion efficiency.Index Terms -L-SSPS, laser-photovoltaic power converter, InGaAs/InGaP system, structural design.