Browsing by Author "Yang, Tung-Ting"

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Antireflective scheme for InGaP/InGaAs/Ge triple junction solar cells based on TiO2 biomimetic structures
(2012)
Hung, Kuo-Hsuan
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Chen, Ting-Gang
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Yang, Tung-Ting
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Yu, Peichen
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Hong, Chung-Yu
In this work, we demonstrate the device design, characterization, fabrication and analysis of biomimetic anti reflective structures on III-V multi-junction solar cell. The cell without anti reflective structure has a severe change of refractive index between the cell and air, causing a huge reflection (about 30%) and decrease the cell efficiency significantly. We can reduce light reflection by coating a proper material on the cell, diminishing the refractive index difference between cell and air interface. The optimization of single antireflection coating and biomimetic structure will be discussed and the experimental results will also be presented.
Compound biomimetic structures for efficiency enhancement of Ga0.5In0.5P/GaAs/Ge triple-junction solar cells
(2014-03-10)
Hung, Mu-Min
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Han, Hau-Vei
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Hong, Chung-Yu
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Hong, Kuo-Hsuan
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Yang, Tung-Ting
Biomimetic nanostructures have shown to enhance the optical absorption of Ga0.5In0.5P/GaAs/Ge triple junction solar cells due to excellent antireflective (AR) properties that, however, are highly dependent on their geometric dimensions. In practice, it is challenging to control fabrication conditions which produce nanostructures in ideal periodic arrangements and with tapered side-wall profiles, leading to sacrificed AR properties and solar cell performance. In this work, we introduce compound biomimetic nanostructures created by depositing a layer of silicon dioxide (SiO2) on top of titanium dioxide(TiO2) nanostructures for triple junction solar cells. The device exhibits photogenerated current and power conversion efficiency that are enhanced by similar to 8.9% and similar to 6.4%, respectively, after deposition due to their improved antireflection characteristics. We further investigate and verify the optical properties of compound structures via a rigorous coupled wave analysis model. The additional SiO2 layer not only improves the geometric profile, but also serves as a double-layer dielectric coating. It is concluded that the compound biomimetic nanostructures exhibit superior AR properties that are relatively insensitive to fabrication constraints. Therefore, the compound approach can be widely adopted for versatile optoelectronic devices and applications. (C)2014 Optical Society of America
Impact of Light Management on Photovoltaic Characteristics of GaAs Solar Cells with Photonic Crystals and Quasi-Photonic Crystals
(2014)
Lai, Yi-Chun
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Yang, Tung-Ting
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Yu, Peichen
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Hung, Mu-Min
;
Charlton, Martin
In detailed balance model, the efficiency of single-junction solar cells can be potentially as high as 33.5% under AM 1.5G illumination. However the best state-of-the-art devices are still far lower than those figures, even the electronic quality is nearly perfect. Therefore the efficiency gap should stem from the light management inside solar cells. Recently, external radiation efficiency (eta ext) derived from detailed balance model is emphasized to evaluate light management and photon recycling, which aggregates the loss of backward emission into substrate and non-radiative recombination. This factor can be highly relevant to the cell\'s performance, especially open-circuit voltage (Voc), and maximizing Voc is generally considered as the last mile to approach ultra-high efficiency limit. In this work, we try to quantify the Voc enhancement in GaAs solar cells by enhancing light extraction. The simulation tools are RCWA simulation and photon recycling model NREL developed recently. The top structures we simulate here are TiO2 cones arranged in three PC/QPC lattices. After our calculation, the QPC 12-folds symmetry can make the biggest Voc enhancement 11.21meV compared with bare one, and the structure also possess extraordinary omni-directional anti-reflection ability for maintaining high Jsc. Our results also show that using this way to enhance Voc is especially suitable for cells with ordinary material quality. Therefore, the requests of ideal top structures for solar cells\' use are not only near-perfect anti-reflection, but the ability to maximize light extraction if no feature of angular filter exists.
Photovoltaic Characteristics of GaAs Solar Cells with Selective Filters
(2015)
Hong, Chung-Yu
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Hung, Mu-Min
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Yang, Tung-Ting
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Wang, Yi-Chin
;
Lin, Yu-Chen
Enhancing the photon recycling process in a solar cell can boost the open-circuit voltage (V-oc). In this work, we employ a selective filter realized by alternative TiO2 and SiO2 dielectric layers with different cutoff wavelengths as the front surface structures, and a distributed Bragg reflector (DBR) grown by epitaxy on the rear side of GaAs solar cells to form an optical cavity. The idea is to suppress the radiative recombination emission loss at the material bandgap toward the front and rear side by increasing photon-recycling via a cavity design with minimal auxiliary impact on light current. From our experiment, when cut-off wavelength was designed at 840nm, the V-oc of the cell increase by 1.1mV compared with the device without the selective filter. Moreover, we successfully developed an optical model that combines a rigorous couple wave analysis (RCWA) and photon recycling calculation NREL developed recently to quantify the V-oc enhancement from different optical design on GaAs solar cells. Based on theoretical optimizations of the experimental data, if we can optimize the back DBR reflector or using metal as the back mirror, we can obtain a large V-oc enhancement by 36.4mV using the selective filter with a cut-off wavelength of 840 nm. However, although we can use selective filter as top structure to improve the V-oc, the power conversion efficiency is still limited due to the implementation of selective filters has affected light absorption at the desired spectral range. Nevertheless, this concept of light management may be further improved by using angular filters in order to prevent the loss of light current while improving the V-oc and power conversion efficiency at the same time.