Browsing by Author "Chen, Chia-Hsiang"

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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
;
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.
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.
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
;
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.
Ultrafast carrier dynamics in Cu(In,Ga)Se-2 thin films probed by femtosecond pump-probe spectroscopy
(2012-06-04)
Chen, Shih-Chen
;
Liao, Yu-Kuang
;
Chen, Hsueh-Ju
;
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