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Now showing 1 - 10 of 35

Wavelength-tunable InGaAs-capped quantum-dot infrared photodetectors for multi-color detection
(2011-05-01)
Lin, Wei-Hsun
;
Lin, Shih-Yen
;
Tseng, Chi-Che
;
Kung, Shu-Yen
;
Chao, Kuang-Ping
A two-terminal quantum-dot infrared photodetector (QDIP) with stacked 5-period InAs/GaAs and InGaAs-capped InAs/GaAs QD structures is investigated in this paper. The device has exhibited distinct responses at mid-wavelength and long-wavelength infrared regions under positive and negative biases, respectively. Also observed for the device are the equal normal absorption ratios under different voltage biases for the device under either MWIR or LWIR ranges. The device has revealed its potential in the application of voltage-tunable and multi-color detections. (C) 2010 Elsevier B.V. All rights reserved.
Efficiency enhancement of non-selenized Cu(In,Ga)Se-2 solar cells employing scalable low-cost antireflective coating
(2014-07-04)
Jheng, Bao-Tang
;
Liu, Po-Tsun
;
Wu, Meng-Chyi
;
光電工程學系
;
顯示科技研究所
In this study, a non-selenized CuInGaSe2 (CIGS) solar device with textured zinc oxide (ZnO) antireflection coatings was studied. The ZnO nanostructure was fabricated by a low-temperature aqueous solution deposition method. With controlling the morphology of the solution-grown tapered ZnO nanorod coatings, the average reflectance of the CIGS solar device decreased from 8.6% to 2.1%, and the energy conversion efficiency increased from 9.1% to 11.1%. The performance improvement in the CuInGaSe2 thin-film solar cell was well explained due to the gradual increase of the refractive index between air and the top electrode of solar cell device by the insertion of the ZnO nanostructure. The results demonstrate a potential application of the ZnO nanostructure array for efficient solar device technology.
A promising sputtering route for dense Cu2ZnSnS4 absorber films and their photovoltaic performance
(2014-09-01)
Jheng, Bao-Tang
;
Liu, Po-Tsun
;
Wu, Meng-Chyi
;
光電工程學系
;
顯示科技研究所
Copper zinc tin sulfide (Cu2ZnSnS4, CZTS) is highly abundant in nature. It is an important absorber material for the development of low-cost and sustainable next-generation I-2-II-IV-VI4 thin-film solar cells because it has a the tunable direct band gap energy, inexpensive constituent elements, and a large absorption coefficient in the visible wavelength region. This work develops an efficient one-step vacuum-based approach to depositing CZTS films without the need to supply excess sulfur during/after deposition or to perform any post-sulfurization treatment. This one-step RF sputtering process produces CZTS films that are crystalline, phase-pure, dense, smooth, and continuous. Air Mass 1.5 G power conversion efficiencies of as high as 6% have been achieved with an antireflection coating, demonstrating that this new approach has great potential as a low-cost alternative for high-efficiency CZTS solar cell production. (C) 2014 Elsevier B.V. All rights reserved.
Solution-Processed Small-Molecule Bulk Heterojunction Ambipolar Transistors
(2014-04-01)
Cheng, Shiau-Shin
;
Huang, Peng-Yi
;
Ramesh, Mohan
;
Chang, Hsiu-Chieh
;
Chen, Li-Ming
Solution-processed small-molecule bulk heterojunction (BHJ) ambipolar organic thin-film transistors are fabricated based on a combination of [2-phenylbenzo[d,d \']thieno[3,2-b;4,5-b \']dithiophene (P-BTDT) : 2-(4-n-octylphenyl)benzo[d,(d) under bar \']thieno[3,2-b;4,5-b\']dithiophene (OP-BTDT)] and C-60. Treating high electrical performance vacuum-deposited P-BTDT organic semiconductors with a newly developed solution-processed organic semiconductor material, OP-BTDT, in an optimized ratio yields a solution-processed p-channel organic semiconductor blend with carrier mobility as high as 0.65 cm(2) V-1 s(-1). An optimized blending of P-BTDT:OP-BTDT with the n-channel semiconductor, C-60, results in a BHJ ambipolar transistor with balanced carrier mobilities for holes and electrons of 0.03 and 0.02 cm(2) V-1 s(-1), respectively. Furthermore, a complementary-like inverter composed of two ambipolar thin-film transistors is demonstrated, which achieves a gain of 115.
Efficiency Improvement of Blue LEDs Using a GaN Burried Air Void Photonic Crystal With High Air Filling Fraction
(2014-05-01)
Liu, Jia-Zhe
;
Charlton, Martin D. B.
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Lin, Chung-Hsiang
;
Lee, Kang-Yuan
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Krishnan, Chirenjeevi
In this paper, we investigate the efficiency enhancement of blue InGaN/GaN light-emitting diodes (LEDs) by incorporating a burried air void photonic crystal (BAVPC) layer within the epitaxial structure. As compared with the conventional patterned sapphire substrate (C-PSS) LEDs and flat sapphire substrate LEDs with BAVPC, the fabricated patterned sapphire substrate (PSS) LEDs with BAVPC exhibit the lowest full-width at half-maximum of (002) and (102) diffraction peaks, the highest light output power of 20.6 mW, and the highest external quantum efficiency of 37.4%. Remarkable performance improvement in the PSS LED with BAVPC is attributed to the better epitaxial quality with threading dislocations terminated by the BAVPC and the higher scattering at interface between GaN and air-void. By positioning the BAVPC directly below the multiple quantum wells (MQWs), it would cause the reduction in the number of trapped optical modes. The methodology optically isolates the MQWs from the underlying substrate and increases the optical output power. Moreover, threading dislocations are significantly suppressed using the BAVPC with high air filling fraction of similar to 50%. It is well proposed that this methodology provides a promising alternative to C-PSS LEDs.
Star-shaped self-assembly of an organic thin film transistor sensor in the presence of Cu2+ and CN- ions
(2014-02-01)
Ramesh, Mohan
;
You, Yuan-Ruei
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Shellaiah, Muthaiah
;
Wu, Meng-Chyi
;
Lin, Hong-Cheu
In this study we developed organic thin film transistors (OTFTs) for the sensing of metal ions and anions through the self-assembly of a pentacene/Schiff base pyrene derivative. Our bilayer OTFTs displayed attractive device parameters: an electron mobility (mu) of 0.12 cm(2) V-1 s(-1), a threshold voltage (Vth) of 22.20 V, and a five-orders-of-magnitude on/off ratio. This device was sensitive toward Cu2+ among 13 metal cations and toward CN among nine anions, as measured through changes in the values of Vth and I-off in the presence of Cu2+ cations and a change in the value of I-sat in the presence of CN anions. We observed selectivity toward both of these ions in mixed ion solutions, with sensitivity over different concentrations (from 20 to 350 mu M for Cu2+; from 100 to 350 mu M for CN ) as well as in sea water. The pyrene derivative self-assembled through pyrene-pyrene coordination in the presence of Cu2+ ions; the rods of the pyrene derivative broke into smaller pieces upon formation of benzoxazole rings in the presence of CN ions, as confirmed using atomic force microscopy and fourier transform attenuated total reflection spectroscopy. (C) 2013 Elsevier B.V. All rights reserved.
Effects of ZnO-nanostructure antireflection coatings on sulfurization-free Cu2ZnSnS4 absorber deposited by single-step co-sputtering process
(2013-07-29)
Jheng, Bao-Tang
;
Liu, Po-Tsun
;
Wang, Min-Chuan
;
Wu, Meng-Chyi
;
電子工程學系及電子研究所
ZnO nanostructures as anti-reflective coatings were synthesized by using hydrothermal technique for a sulfurization-free Cu2ZnSnS4 absorber prepared by co-sputtering deposition. By controlling the morphology of solution-grown ZnO nanostructures, the average reflectance of the Cu2ZnSnS4 solar cell with branched ZnO nanorods decreased from 7.6% to 1.12%, and the energy conversion efficiency promoted by 10.4% from the initial value of 4.8% to 5.3%. The efficiency improvement was well studied with the effects of the gradually increased refractive index between the air and the top electrode of Cu2ZnSnS4 solar device, due to the presence of the ZnO nanostructure. (C) 2013 AIP Publishing LLC.
Long-wavelength electroluminescence of InGaAs-capped type-II GaSb/GaAs quantum-rings at room temperature
(2013-09-01)
Lin, Wei-Hsun
;
Wang, Kai-Wei
;
Lin, Shih-Yen
;
Wu, Meng-Chyi
;
光電學院
The room-temperature photoluminescence (PL) and electroluminescence (EL) exceeding 1.3 mu m are observed for InGaAs-capped GaSb quantum-ring (QR) structures. With increasing In composition, the emission wavelength would shift from 1.18 to 131 mu m. The InGaAs-capped GaSb QRs also exhibit a higher injection current and stronger EL intensity at the same applied voltage. With the observation of low-temperature PL spectra, the transition mechanisms of the standard and InGaAs-capped QRs are further investigated. (c) 2012 Elsevier B.V. All rights reserved.
Temperature-dependent photoluminescence and carrier dynamics of standard and coupled type-II GaSb/GaAs quantum rings
(2013-09-01)
Lin, Wei-Hsun
;
Wang, Kai-Wei
;
Lin, Shih-Yen
;
Wu, Meng-Chyi
;
光電學院
Temperature-dependent photoluminescence (PL) and the corresponding carrier dynamics of standard and coupled type-II GaSb/GaAs quantum rings (QRs) are investigated in this article. Compared with standard QRs, the slower PL intensity decay of coupled QRs with increasing temperature is attributed to the depression of thermal quenching. More intense PL intensity is also observed for the coupled-QR sample at room temperature. With further reducing the GaAs spacer layer thickness to 2 nm, near two-times PL enhancement is observed. The results indicate that with the enhanced luminescence intensity of coupled-QR structure, type-II nano-structures may be utilized for light-emitting device applications. (c) 2013 Elsevier B.V. All rights reserved.
Solution-processed benzotrithiophene-based donor molecules for efficient bulk heterojunction solar cells
(2013)
Patra, Dhananjaya
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Chiang, Chao-Cheng
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Chen, Wei-An
;
Wei, Kung-Hwa
;
Wu, Meng-Chyi
In this study we used convergent syntheses to prepare two novel acceptor-donor-acceptor (A-D-A) small molecules (BT4OT, BT6OT), each containing an electron-rich benzotrithiophene (BT) unit as the core, flanked by octylthiophene units, and end-capped with electron-deficient cyanoacetate units. The number of octylthiophene units affected the optical, electrochemical, morphological, and photovoltaic properties of BT4OT and BT6OT. Moreover, BT4OT and BT6OT possess low-energy highest occupied molecular orbitals (HOMOs), providing them with good air stability and their bulk heterojunction (BHJ) photovoltaic devices with high open-circuit voltages (V-oc). A solar cell device containing BT6OT and [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) in a 1 : 0.75 ratio (w/w) exhibited a power conversion efficiency (PCE) of 3.61% with a short-circuit current density (J(sc)) of 7.39 mA cm(-2), a value of V-oc of 0.88 V, and a fill factor (FF) of 56.9%. After adding 0.25 vol% of 1-chloronaphthalene (CN) as a processing additive during the formation of the blend film of BT6OT: PC71BM (1 : 0.75, w/w), the PCE increased significantly to 5.05% with values of J(sc) of 9.94 mA cm(-2), V-oc of 0.86 V, and FF of 59.1% as a result of suppressed nanophase molecular aggregation.

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