Browsing by Author "Lai, Chih-Huang"

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Fabrication of large-scale single-crystal Cu(In, Ga)Se-2 nanotip arrays solar cell by one-step ion milling processes
(2013-11-01)
Wang, Yi-Chung
;
Yen, Yu-Ting
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Liu, Chin-Hung
;
Chen, Chia-Hsiang
;
Kuo, Wei-Chen
Template-free, one step formation of Cu(In, Ga)Se-2 (CIGS) nanotip arrays (NTRs) to enhance device efficiency were discussed. Through Ar+ ion milling process, the CIGS NTRs could be formed directly on the CIGS layer. The angles and lengths of CIGS NTRs could be precisely controlled by incident angle of Ar+ beam and milling time, respectively. Mechanisms were proposed to be a self-masking effect by Cu segregation formed at early stage confirmed by Transmission Electron Microscopy, Grazing Incidence X-ray Diffraction, Energy Dispersive Spectroscopy, and Auger Electron Spectroscopy. Measurements of devices on various KCN washing time and thickness of CdS buffer layer were reported to achieve the highest efficiency of CIGS NTRs devices. This approach provides one-step fast process without templates, easy integration with in-line sputtering process, and no post-selenizatoin process for the formation of CIGS nanostructure, which can stimulate great attention not only in academic investigations but also in industrial side for practical applications. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.
Interplay between potassium doping and bandgap profiling in selenized Cu(In,Ga)Se-2 solar cells: A functional CuGa: KF surface precursor layer
(2018-05-01)
Cai, Chung-Hao
;
Chen, Rong-Zhi
;
Chan, Ting-Shan
;
Lu, Ying-Rui
;
Huang, Wei-Chih
The progress of selenized Cu(In,Ga)Se-2 (CIGSe) solar cells is limited by low open-circuit voltage (Voc), which results from the Ga-deficient surface and undesirable bandgap profile after selenization. Controlling the Ga grading, especially on the CIGSe surface, is challenging but critical for further efficiency improvement. Here, the simple sputtering route with K incorporation is presented to engineer single-or double-graded bandgap. The K incorporation through sputtered precursors can considerably affect the Ga profile in CIGSe during selenization, essentially distinct from reported KF post-deposition treatment, in which the Ga profile keeps unchanged. Using synchrotron-based X-ray absorption spectroscopy and first-principle calculations, we verify that Ga diffusion via Cu vacancies is restrained due to the presence of K-Cu defects. Therefore, by introducing a CuGa:KF surface layer on the bi-layer precursors, the surface Ga content of CIGSe is increased effectively, achieving a notch-like Ga distribution after selenization. This unique CuGa: KF layer significantly boosts the Voc and yields over 15% efficiency, even with a low reactive Se vapor for selenization. Our approach, completely compatible with the existing fabrication process, offers a new direction for engineering band structure without sulfurization.
Large Scale Single-Crystal Cu(In,Ga)Se(2) Nanotip Arrays For High Efficiency Solar Cell
(2011-10-01)
Liu, Chin-Hung
;
Chen, Chia-Hsiang
;
Chen, Szu-Ying
;
Yen, Yu-Ting
;
Kuo, Wei-Chen
In this paper, we demonstrated direct formation of large area Cu(In,Ga)Se(2), nanotip arrays (GIGS NTRs) by using one step Ar(+) milling process without template. By controlling milling time and incident angles, the length of CIGS NTRs with adjustable tilting orientations can be precisely controlled. Formation criteria of these CIGS NTRs have been discussed in terms of surface curvature, multiple components, and crystal quality, resulting in a highly anisotropic milling effect. The CIGS NTRs have very low reflectance <0.1% at incident wavelengths between 300 to 1200 nm. Open circuit voltage and short circuit current of CIGS NTRs solar cell were measured to be similar to 390 mV and similar to 22.56 mA/cm(2), yielding the filling factor and the efficiency of 59 and 5.2%, respectively. In contrast to CIGS thin film solar cell with efficiency of 3.2%, the nanostructured CIGS NTRs can have efficiency enhancement of similar to 160% due to the higher light absorption ability because of the nanostructure. The merits of current approach include the latest way via template-free direct creating process of nanostructured CIGS NTRs with controllable dimensionality and large scale production without postselenization process.
Large Scale Single-Crystal Cu(In,Ga)Se-2 Nanotip Arrays For High Efficiency Solar Cell
(2011-10-01)
Liu, Chin-Hung
;
Chen, Chia-Hsiang
;
Chen, Szu-Ying
;
Yen, Yu-Ting
;
Kuo, Wei-Chen
In this paper, we demonstrated direct formation of large area Cu(In,Ga)Se-2, nanotip arrays (GIGS NTRs) by using one step Ar+ milling process without template. By controlling milling time and incident angles, the length of CIGS NTRs with adjustable tilting orientations can be precisely controlled. Formation criteria of these CIGS NTRs have been discussed in terms of surface curvature, multiple components, and crystal quality, resulting in a highly anisotropic milling effect. The CIGS NTRs have very low reflectance <0.1% at incident wavelengths between 300 to 1200 nm. Open circuit voltage and short circuit current of CIGS NTRs solar cell were measured to be similar to 390 mV and similar to 22.56 mA/cm(2), yielding the filling factor and the efficiency of 59 and 5.2%, respectively. In contrast to CIGS thin film solar cell with efficiency of 3.2%, the nanostructured CIGS NTRs can have efficiency enhancement of similar to 160% due to the higher light absorption ability because of the nanostructure. The merits of current approach include the latest way via template-free direct creating process of nanostructured CIGS NTRs with controllable dimensionality and large scale production without postselenization process.
Misorientation Control and Functionality Design of Nanopillars in Self-Assembled Perovskite-Spinel Heteroepitaxial Nanostructures
(2011-05-01)
Liao, Sheng-Chieh
;
Tsai, Pei-Yu
;
Liang, Chen-Wei
;
Liu, Heng-Jui
;
Yang, Jan-Chi
In this study, advanced control of crystallographic orientations and magnetic properties of self-assembled nanostructures via rational selections of substrates is demonstrated. We show that in the perovskite spinel BiFeO(3)-CoFe(2)O(4) model system the crystal orientation of self-assembled CoFe(2)O(4) nanopillars can be tuned among (001), (011), and (111), while that of the BiFeO(3) matrix is fixed in (001). Moreover, the resultant CoFe(2)O(4) nanopIllars appear in various shapes: pyramid, roof, and triangular platform, respectively. The tunable nanostructures through this approach enable the control of material functionality such as the magnetic anisotropy of CoFe(2)O(4). This study opens a new pathway for the engineering of self-assembled heteroepitaxial nanostructures.
Non-antireflective Scheme for Efficiency Enhancement of Cu(In,Ga)Se-2 Nanotip Array Solar Cells
(2013-08-01)
Liao, Yu-Kuang
;
Wang, Yi-Chung
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Yen, Yu-Ting
;
Chen, Chia-Hsiang
;
Hsieh, Dan-Hua
We present systematic works in characterization of CIGS nanotip arrays (CIGS NTRs). CIGS NTRs are obtained by a one-step ion-milling process by a direct-sputtering process of CIGS thin films (CIGS TF) without a postselenization process. At the surface of CIGS NTRs, a region extending to 100 nm in depth with a lower copper concentration compared to that of CIGS TF has been discovered. After KCN washing, removal of secondary phases can be achieved and a layer with abundant copper vacancy (V-Cu) was left. Such compositional changes can be a benefit for a CIGS solar cell by promoting formation of Cd-occupied Cu sites (Cd-Cu) at the CdS/CIGS interface and creates a type-inversion layer to enhance interface passivation and carrier extraction. The raised V-Cu concentration and enhanced Cd diffusion in CIGS NTRs have been verified by energy dispersive spectrometry. Strengthened adhesion of Al:ZnO (AZO) thin film on CIGS NTRs capped with CdS has also been observed in SEM images and can explain the suppressed series resistance of the device with CIGS NTRs. Those improvements in electrical characteristics are the main factors for efficiency enhancement rather than antireflection.
Self-Assembled BiFeO3-epsilon-Fe2O3 Vertical Heteroepitaxy for Visible Light Photoelectrochemistry
(2016-09-21)
Le Thi Quynh
;
Chien Nguyen Van
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Bitla, Yugandhar
;
Chen, Jhih-Wei
;
Thi Hien Do
Self-assembled vertical heterostructure with a high interface-to-volume ratio offers tremendous opportunities to realize intriguing properties and advanced modulation of functionalities. Here, a heterostructure composed of two visible-light photocatalysts, BiFeO3 (BFO) and epsilon-Fe2O3 (epsilon-FO), is designed to investigate its photoelectrochemical performance. The structural characterization of the BFO-FO heterostructures confirms the phase separation with BFO nanopillars embedded in the epsilon-FO matrix. The investigation of band structure of the heterojunction suggests the assistance of photoexcited carrier separation, leading to an enhanced photoelectrochemical performance. The insights into the charge separation are further revealed by means of ultrafast dynamics and electrochemical impedance spectroscopies. This work shows a delicate design of the self-assembled vertical heteroepitaxy by taking advantage of the intimate contact between two phases that can lead to a tunable charge interaction, providing a new confi guration for the optimization of photoelectrochemical cell.
Self-Assembled Epitaxial Core-Shell Nanocrystals with Tunable Magnetic Anisotropy
(2015-09-02)
Liao, Sheng-Chieh
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Chen, Yong-Lun
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Kuo, Wei-Cheng
;
Cheung, Jeffrey
;
Wang, Wei-Cheng
Sharp variation in coercivity and magnetic interactions in patterned CoxNi1-x nanoarrays
(2013-08-14)
Yang, Chao-Yao
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Wang, Liang-Wei
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Chen, Po-An
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Lin, Hong-Ji
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Lai, Chih-Huang
We present a study concerning the unexpectedly large coercivity increase and associated magneto-structural properties of CoxNi1-x patterned arrays. An increase in x led to an face-center-cubic (FCC)-> hexagonal-close-packed (HCP) transition in CoxNi1-x arrays, accompanied by a 6-fold increase in coercivity and strong 3d exchange interactions probed by x-ray magnetic circular dichroism. Sum-rule analysis revealed that orbital moment involved very little in the variable coercivity and magnetic anisotropy; this is distinct from other nanostructures displaying variable coercivity. The sharp rise in coercivity can be attributed to the geometrical confinement of the arrays, causing the microstructure of the nano-clusters to switch magnetization reversal mechanism from fanning to coherent with increasing x, based on the chain-of-spheres model. First-order-reversal curves revealed that the FCC and HCP arrays comprised both soft and hard ferromagnetic components; however, the soft component of the FCC was much more pronounced, leading to differences in reversibility. This type of nanostructure provides a sharp control of magnetic hardness that could be tailored in related technologies. (C) 2013 AIP Publishing LLC.
Strong magnetic enhancement in self-assembled multiferroic-ferrimagnetic nanostructures
(2013)
Chen, Ying-Jiun
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Hsieh, Ying-Hui
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Liao, Sheng-Chieh
;
Hu, Zhiwei
;
Huang, Meng-Jie
In the past decade, self-assembled vertical nano-heterostructures have drawn considerable attention because a high interface-to-volume ratio can be used to tailor or create functionalities. We have systematically investigated the magnetic properties of oxide heterostructures consisting of the CoFe2O4 nanopillars embedded in the BiFeO3 matrix using macroscopic magnetization measurements and element-selective soft X-ray absorption magnetic circular dichroism (XMCD) at the Co- and Fe-L-2,L-3 edge. The magnetization and XMCD data show that the total ordered magnetic moment of Co2+ in CoFe2O4-BiFeO3 nano-heterostructures is strongly enhanced. This study clearly indicates that the high interface-to-volume ratio vertical nanostructure creates a strong ferromagnetic and antiferromagnetic magnetic coupling via an interface. Furthermore, the magnetic coupling can be tuned in the multiferroic-ferrimagnetic self-assembled heterostructures by controlling the spacing between nanopillars.
Tuning the formation and functionalities of ultrafine CoFe2O4 nanocrystals via interfacial coherent strain
(2013)
Hsieh, Ying-Hui
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Kuo, Ho-Hung
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Liao, Sheng-Chieh
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Liu, Heng-Jui
;
Chen, Ying-Jiun
Complex oxide nanocrystals with a spinel structure show their remarkable optical, electronic, mechanical, thermal, and magnetic properties. In this study, we present a simple yet versatile strategy to grow self-assembled epitaxial CoFe2O4 nanocrystals with well-controlled size (less than 10 nm) and single orientation. CoFe2O4 nanocrystals were fabricated via phase separation in a BiFeO3-CoF2O4 ultrathin film by pulsed laser deposition. The coherent strain at the BiFeO3-CoF2O4 interface suppressed the growth of the nanocrystals regardless of substrate temperatures. This strain also resulted in the ferromagnetic anisotropy and interesting conducting behaviors of ultrafine CFO nanocrystals.
Tuning the functionalities of a mesocrystal via structural coupling
(2015-07-14)
Liu, Heng-Jui
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Liu, Yun-Ya
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Tsai, Chih-Ya
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Liao, Sheng-Chieh
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Chen, Ying-Jiun
In the past decades, mesocrystal, a kind of nanocrystals with specific crystallographic orientation, has drawn a lot of attention due to its intriguing functionalities. While the research community keeps searching for new mesocrystal systems, it is equally crucial to develop new approaches to tune the properties of mesocrystals. In this work, a self-organized two-dimensional mesocrystal composed of highly oriented CoFe2O4 (CFO) nano-crystals with assistance of different perovskite matrices is studied as a model system. We have demonstrated that the strain state and corresponding magnetic properties of the CFO mesocrystal can be modulated by changing the surrounding perovskite matrix through their intimate structural coupling. Interestingly, this controllability is more strongly correlated to the competition of bonding strength between the matrices and the CFO mesocrystals rather than the lattice mismatch. When embedded in a matrix with a higher melting point or stiffness, the CFO mesocrystal experiences higher out-of-plane compressive strain and shows a stronger magnetic anisotropy as well as cation site-exchange. Our study suggests a new pathway to tailor the functionalities of mesocrystals.
Tuning the magnetic properties of self-assembled BiFeO3-CoFe2O4 heteroepitaxy by magneto-structural coupling
(2016)
Amrillah, Tahta
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Vandrangi, Suresh K.
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Bitla, Yugandhar
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Do, Thi Hien
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Liao, Sheng-Chieh
Magnetic and multiferroic nanocomposites with two distinct phases have been a topic of intense research for their profound potential applications in the field of spintronics. In addition to growing high-quality phase separated heteroepitaxial nanocomposites, the strain engineering that is conducive to enhance the tunability of material properties, in general, and the magnetic properties, in particular, is of utmost importance in exploring new possibilities. Here, we investigated the magneto-structural coupling between anti-ferromagnetic BiFeO3 (BFO) and ferrimagnetic CoFe2O4 (CFO) in self-assembled vertically aligned nanocomposites grown on LaAlO3 (LAO) and SrTiO3 (STO) substrates. We found that BFO exhibits tetragonal (T) and rhombohedral (R) structures as the stable phases and CFO has high magnetocrystalline anisotropy even in the form of nanocomposites. The temperature and magnetic field dependent magnetizations of T_ BFO-CFO/LAO and R_ BFO-CFO/STO nanocomposites primarily demonstrate the magnetoelastic coupling between these variants.
Ultrafast carrier dynamics in Cu(In,Ga)Se-2 thin films probed by femtosecond pump-probe spectroscopy
(2012-06-04)
Chen, Shih-Chen
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Liao, Yu-Kuang
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Chen, Hsueh-Ju
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Chen, Chia-Hsiang
;
Lai, Chih-Huang
Ultrafast carrier dynamics in Cu(In,Ga)Se-2 films are investigated using femtosecond pump-probe spectroscopy. Samples prepared by direct sputtering and co-evaporation processes, which exhibited remarkably different crystalline structures and free carrier densities, were found to result in substantially different carrier relaxation and recombination mechanisms. For the sputtered CIGS films, electron-electron scattering and Auger recombination was observed, whereas for the co-evaporated CIGS films, bandgap renormalization accompanied by band filling effect and hot phonon relaxation was observed. The lifetime of defect-related recombination in the co-evaporated CIGS films is much longer than that in the direct-sputtered CIGS films, reflecting a better quality with higher energy conversion efficiency of the former. (c) 2012 Optical Society of America
Using magnetic structure of Co40Pd60/Cu for the sensing of hydrogen
(2017-07-10)
Lang, Jaw-Yeu
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Pai, Yun-Chieh
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Lam, Tu-Ngoc
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Lin, Wen-Chin
;
Chan, Ting-Shan
This paper reports on a magnetic device with a [Co40Pd60/Cu](10)/Fe structure for use in the detection of H-2. In a magneto-optical, transport, and gas-detection system, the proposed device presented sharp, reproducible H-2-dependent magnetic/electrical properties. The device's saturation magnetization (induced resistance change) dropped (increased) by a factor of similar to 5 when a H-2 pressure of 75 kPa is given. Besides, the electrical signal-to-noise ratio of the device can be restored similar to 50% by exposing it to a magnetic field of 1000 Oe, even when the sensitivity of the device dropped at a low H-2 pressure (0.7 KPa). This demonstrates the applicability of the device for use as a low-pressure H-2 detector. Operando x-ray spectroscopy revealed that changes in H-2-induced magnetism arose from a Co-Pd charge transfer effect coupled to changes in the local-structure symmetry. Published by AIP Publishing.