Effect of the Quantum Size Effect on the Performance of Solar Cells with a Silicon Nanowire Array Embedded in SiO 2
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Effect of the Quantum Size Effect on the Performance of Solar Cells with a Silicon Nanowire Array Embedded in SiO2 Yasuyoshi Kurokawa1,2, Shinya Kato1, Yuya Watanabe1, Akira Yamada1,3, Makoto Konagai1,3, Yoshimi Ohta4, Yusuke Niwa4, Masaki Hirota4 1 Department of Physical Electronics, Tokyo Institute of Technology, 2-12-1-S9-10 O-okayama, Meguro-ku, Tokyo 152-8552, Japan 2 PRESTO, JST, 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan 3 Photovoltaics Research Center (PVREC), Tokyo Institute of Technology, 2-12-1-S9-10 Ookayama, Meguro-ku, Tokyo 152-8552, Japan 4 Advanced Materials Laboratory, Nissan Research Center, 1 Natsushima-cho, Yokosuka-shi, Kanagawa 237-8523, Japan ABSTRACT The electrical characteristics of silicon nanowire (SiNW) solar cells with p-type hydrogenated amorphous silicon oxide (Eg=1.9 eV)/n-type SiNWs embedded in SiO2/n-type hydrogenated amorphous silicon (Eg=1.7 eV) structure have been investigated using a twodimensional device simulator with taking the quantum size effects into account. The average bandgap of a SiNW embedded in SiO2 increased from 1.15 eV to 2.71 eV with decreasing the diameter from 10 nm to 1 nm due to the quantum size effect. It should be noted that under the sunlight with AM1.5G the open-circuit voltage (Voc) of SiNW solar cells also increased to 1.54 V with decreasing the diameter of the SiNWs to 1 nm. This result suggests that it is possible to enhance the Voc by the quantum size effect and a SiNW is a promising material for the all silicon tandem solar cells. INTRODUCTION Recently many researchers have shown an interest in silicon nanostructures, such as silicon quantum dots [1,2], silicon nanowires (SiNW) [3-5] and so on, to apply to solar cell structure. Since a SiNW embedded in a wide-gap material can make carriers confined in it, the bandgap can be tuned due to the quantum size effect. Thus, it is possible to apply the SiNW to all silicon tandem solar cells [6], which have possibility to overcome the Shockley-Queisser limit [7]. There is little study to apply the quantum size effect to SiNW solar cell structure. Kurstjens et al. fabricated 2.5-13 nm diameter SiNW arrays with 193 nm DUV immersion lithography, dry etching, and post-oxidation [8]. Kato et al., have fabricated diameter-controlled SiNW arrays to metal assisted chemical etching with silica nanoparticles (MACES) to apply to the solar cell structure [9]. However, a detailed analysis of the electrical properties of SiNW solar cells has been also little investigated, although there are some studies about numerical simulation of the optical properties of SiNWs [10]. It is needed to understand influences which quantum confinement gives the electrical properties of SiNWs. In this paper, we numerically analyze the effects of wire diameter on electrical properties of SiNW solar cells with taking quantum effects into account. Especially, the quantum size effect on the open-circuit voltage (Voc) was investigated, since Voc is the most important factor to realize tandem solar cells with high efficiency.
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