Size-Controlled Silicon Quantum Dots Superlattice for Thin-Film Solar Cell Applications
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1101-KK12-01
Size-Controlled Silicon Quantum Dots Superlattice for Thin-Film Solar Cell Applications Yasuyoshi Kurokawa, Shinsuke Miyajima, Akira Yamada, and Makoto Konagai Department of Physical Electronics, Tokyo Institute of Technology, 2-12-1-S9-9, O-okayama, Meguro-ku, Tokyo, 152-8552, Japan ABSTRACT We prepared size-controlled silicon quantum dots superlattices (Si-QDSLs) by thermal annealing of stoichiometric hydrogenated amorphous silicon carbide (a-SiC:H)/silicon rich hydrogenated amorphous silicon carbide (a-Si1+xC:H) multilayers. Transmission electron microscope (TEM) observation revealed that the size of silicon quantum dots can be controlled by the thickness of the a-Si1+xC:H layers. It was found that hydrogen plasma treatment (HPT) significantly enhanced the photoluminescence (PL) of the Si-QDSLs. From the results of the PL measurement, the bandgap of the Si-QDSLs can be controlled from 1.1 eV to 1.6 eV by varying the diameter of silicon quantum dots. ESR measurement indicated that HPT reduced the defect density in a Si-QDSL from 1.83 ×1019 to 1.67 ×1018 cm-3.
INTRODUCTION Recently, silicon nanocrystals have attracted our interest as one of the candidates of the application for the third generation solar cells [1]. Silicon nanocrystals have unique quantum effects, such as quantum size effect and multi-exciton generation effect [2]. It was reported that these effects lead to enhance the conversion efficiency of solar cells [3,4]. For the purpose to utilize the quantum size effect, we adopted silicon quantum dots superlattice structure (SiQDSL), in which silicon quantum dots are periodically aligned in an amorphous silicon carbide (SiC) matrix, as a candidate of the new material. Since the bandgap is able to be tuned by controlling the size of silicon quantum dots, it is possible to apply for all silicon tandem solar cells (Figure 1). Preparations of Si-QDSL were reported by several researchers [1,5]. They demonstrated that bandgap of a silicon quantum dot (Si-QD) in an amorphous silicon oxide (aSiO2) or nitride (a-Si3N4) matrix can be controlled by changing the dot size. Little study has been done to prepare Si-QDSL using an amorphous silicon carbide (a-SiC) [6,7]. Our calculations based on Kronig-Penney model pointed out that minibands are easily formed in a Si-QD/a-SiC superlattice compared with in a Si-QD/a-SiO2 or Si-QD/a-Si3N4 superlattice. In addition, Jiang et al. reported that Bloch carrier mobility is higher in a Si-QD/a-SiC superlattice than in a Si-QD/aSiO2 or Si-QD/a-Si3N4 superlattice [8]. Therefore, the Si-QD/a-SiC superlattice is a promising material for all silicon tandem solar cells. In this study, we have investigated the structural and optical properties of Si-QDSLs prepared using a-SiC superlattice. The effects of hydrogen plasma treatment (HPT) [9] for reducing defects in the Si-QDSLs are also discussed.
Conduction band (Wide gap material) Mini band Quantum Dot
Band gap
Mini band Valence band (Wide gap material) Figure 1. Schematic diagram of the band structure in Si-QDSL.
Si
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