Browsing by Author "Hoshi, Yusuke"

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Effect of ALD-Al2O3 Passivated Silicon Quantum Dot Superlattices on p/i/n(+) Solar Cells
(2017-07-01)
Rahman, Mohammad Maksudur
;
Tsai, Yi-Chia
;
Lee, Ming-Yi
;
Higo, Akio
;
Li, Yiming
The photovoltaic (PV) nature of the silicon (Si) quantum dot super lattice (QDSL) is studied with an atomic-layer-deposited aluminum oxide film (ALD-Al2O3) and a conventional sputtered-grown amorphous silicon carbide film (a-SiC). The QDSL structures act as an intermediate layer in a p/i/n(+) Si solar cell. The QDSL consists of 4-nm Si on 2-nm SiC nanodisks (NDs) arrayed in an ALD-Al2O3 and a-SiC passivation matrix. Formation of Si-NDs was confirmed by bright field scanning transmission electron microscope. A significant PV response in generating a high photocurrent density J(sc) of 30.15mA/cm(2), open circuit voltage V-oc of 0.50 V, fill factor FF of 0.61, and efficiency. of 9.12% was observed in ALD-Al2O3/QDSL solar cell with respect to a-SiC/QDSL solar cell with J(sc) of 26.94 mA/cm(2), V-oc of 0.50 V, FF of 0.47, and eta of 6.42%. A wide range of photo-carrier transports by the ALD-Al2O3/QDSL structure is possible in the external quantum efficiency spectra with respect to a-SiC/QDSL solar cell. The enhanced PV performance of the QD solar cells was clarified in terms of simulating the absorption contributions for all possible transitions in the nanostructure with different passivation films.
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
;
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.