Browsing by Author "Igarashi, Makoto"

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50% Efficiency Intermediate Band Solar Cell Design Using Highly Periodical Silicon Nanodisk Array
(2012)
Hu, Weiguo
;
Igarashi, Makoto
;
Lee, Ming-Yi
;
Li, Yiming
;
Samukawa, Seiji
A high-quality Si nanodisk superlattice is fabricated by our top-down process. For the first time, a 3D finite element method (FEM) is developed to calculate energy band structure, optical and electrical properties, as well as the intermediate band solar cell (IBSC) operation for the realistic structure. Both the experiments and simulations reveal that miniband formation enhances the optical and electrical collections. Consequently, detailed electronic structure and conversion efficiency are examined to guide optimal design of minibands. A theoretically predicted maximal efficiency of the explored Si nanodisk superlattice is 50.3%, which is promising, compared with well-known complicated Si tandem solar cells.
Impact of silicon quantum dot super lattice and quantum well structure as intermediate layer on p-i-n silicon solar cells
(2016-06)
Rahman, Mohammad Maksudur
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Lee, Ming-Yi
;
Tsai, Yi-Chia
;
Higo, Akio
;
Sekhar, Halubai
The photovoltaic effect of the silicon (Si)/silicon carbide (SiC) quantum dot super lattice (QDSL) and multi-quantum well (QW) strucutres is presented based on numerical simulation and experimental studies. The QDSL and QW structures act as an intermediate layer in a p-i-n Si solar cell. The QDSL consists of a stack of four 4-nm Si nano disks and 2-nm SiC barrier layers embedded in a SiC matrix fabricated with a top-down etching process. The Si nano disks were observed with bright field-scanning transmission electron microscopy. The simulation results based on the 3D finite element method confirmed that the quantum effect on the band structure for the QDSL and QW structures was different and had different effects on solar cell operation. The effect of vertical wave-function coupling to form a miniband in the QDSL was observed based on the solar-cell performance, showing a dramatic photovoltaic response in generating a high photocurrent density J(sc) of 29.24mA/cm(2), open circuit voltage V-oc of 0.51V, fill factor FF of 0.74, and efficiency eta of 11.07% with respect to a i-QW solar cell with J(sc) of 25.27mA/cm(2), V-oc of 0.49V, FF of 0.69, and eta of 8.61% and an i-Si solar cell with J(sc) of 27.63mA/cm(2), V-oc of 0.55V, FF of 0.61, and eta of 10.00%. A wide range of photo-carrier transports by the QD arrays in the QDSL solar cell is possible in the internal quantum efficiency spectra with respect to the internal quantum efficiency of the i-QW solar cell. Copyright (C) 2015 John Wiley & Sons, Ltd.
Modeling miniband for realistic silicon nanocrystal array
(2013-07-01)
Hu, Weiguo
;
Budiman, Mohd Fairuz
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Igarashi, Makoto
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Lee, Ming-Yi
;
Li, Yiming
Within the envelop-function framework, we developed the finite element method to calculate the minibands in the realist Silicon nanocrystal array. This method clearly reveals the miniband formation and accurately calculates the E-K dispersion relationship. In the simple 1D array, the deduced miniband structure matches well with the analytic Kronig-Penney method. More importantly, it can better simulate the 2D and 3D nanocrystal array, which avoids approximations of the quantum cubic box and the independent periodic potential of the multi-dimension Kronig-Penney method. Further, this model is utilized to calculate miniband structure of realistic 2D-array Silicon nanodisk array for guiding quantum dot solar cell design. (C) 2012 Elsevier Ltd. All rights reserved.
Realistic quantum design of silicon quantum dot intermediate band solar cells
(2013-07-05)
Hu, Weiguo
;
Igarashi, Makoto
;
Lee, Ming-Yi
;
Li, Yiming
;
Samukawa, Seiji
A highly periodical Si nanodisk superlattice has been fabricated by our top-down process. Based on the realistic structure, a 3D simulation program using the finite element method is developed to calculate energy band structure, optical and electrical properties, as well as the intermediate band solar cell operation. Both the experiments and simulations reveal that miniband formation enhances the optical and electrical collections. Consequently, detailed electronic structure and conversion efficiency are examined to guide the optimal design of minibands. A theoretically predicted maximal efficiency of the explored Si nanodisk superlattice is 50.3%, which is promising, compared with well-known complicated Si tandem solar cells.
Type-II Ge/Si Quantum Dot superlattice for Intermediate-band Solar Cell Applications
(2013)
Hu, Weiguo
;
Fauzi, Mohd Erman
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Igarashi, Makoto
;
Higo, Akio
;
Lee, Ming-Yi
A Ge/Si type-II quantum dot (QD) has been developed for use in all-Si intermediate-band solar cell (IBSC) applications. A top-down process is used to fabricate the ultra-high-quality QD superlattice. A newly developed 3D finite element method was used to solve several key design problems in achieving a practical structure. Theoretical calculations revealed that a heavy hole state can act as an ideal intermediate band when the interdot space ranges from 0.5 to 4 nm. An IBSC based on this superlattice dramatically enhanced conversion efficiency for concentration applications. For one-sun applications, H-passivizing Si and/or regrowthing amorphous SiC have a great potential to improve the conversion efficiency.