The Optical Analysis and Application of Size-controllable Si Quantum Dots Fabricated by Multi-hollow Discharge Plasma Ch
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The Optical Analysis and Application of Size-controllable Si Quantum Dots Fabricated by Multi-hollow Discharge Plasma Chemical Vapor Deposition Hyunwoong Seo1,2, Yuting Wang1, Giichiro Uchida1, Kunihiro Kamataki1, Naho Itagaki1, Kazunori Koga1, and Masaharu Shiratani1,2 1 Graduate School of Information Science and Electrical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan 2 Center of Plasma Nano-interface Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan ABSTRACT Quantum dot-sensitized solar cells (QDSCs) based on the multiple exciton generation (MEG) of QD are attractive in the field of photochemical cells because the improvement of conventional sensitized solar cells has been stagnant recently. The distinctive characteristics of QDs are their strong photo-response in the visible region and quantum confinement effects. Its theoretical efficiency is much higher than that of solar cell based on the single exciton generation (SEG). Moreover, QDs have tunable optical properties and band-gaps depending on the particle size. But QD materials widely used for QDSC have some disadvantages of toxicity and scarcity. On the other hand, Si as one of good QD materials is abundant and not toxic. Also, Si QD has high stability against light soaking and a high optical absorption coefficient due to quantum size effects. However, the research on Si QD is rare although the quantum effect of Si was already verified. It is one of reasons that the fabrication and collection of Si nano-particles are too difficult. Therefore, this work proposed multi-hollow plasma discharge chemical vapor deposition (CVD). It is possible to collect Si particles unlike conventional CVD and solve the problems of the wet process. The optical properties of Si particles were controlled by varying experimental conditions. In this work, Si particles were fabricated with various sizes and their characteristics were analyzed. Based on the results, Si QD was applied to Si QDSC. INTRODUCTION QD has attracted considerable attraction in the research field of photochemical cells such as dye-sensitized and organic solar cells. Its unique characteristics are advantageous as light harvesting assembly in the photovoltaics. Size quantization allows tuning the photo-response and varying the band gaps to modulate the charge transfer according to different sized particles [1-3]. In addition, QD based on the MEG is able to generate multiple photo-excited electrons by the absorption of a single photon. Therefore, QDSCs have the potential to improve the photovoltaic performance and reduce heat loss while conventional sensitized solar cells based on the SEG generate one photo-excited electron by the absorption of a single photon and have about 47% of heat loss by the extra energy. Accordingly, the theoretical efficiency of QDSC is 11% higher than that of conventional one [4]. There are many kinds of QDs such as CdSe, CdS, PbSe, PbS, and Ag2S developed so far [5-8]. Cd based solar cell has the best conversion efficiency at
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