Browsing by Author "Hsieh, Tung-Po"

Now showing 1 - 12 of 12

A look into the origin of shunt leakage current of Cu(In,Ga)Se-2 solar cells via experimental and simulation methods
(2013-10-01)
Liao, Yu-Kuang
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Kuo, Shou-Yi
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Hsieh, Ming-Yang
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Lai, Fang-I
;
Kao, Ming-Hsuan
This study investigates how to apply space-charge-limited (SCL) current to describe shunt leakage current in a CIGS solar cell. Possible factors inducing SCL current have been observed through conductive atomic force microscopy (C-AFM), which supports the SCL current theory, describing the shunt current of a CIGS solar cell. In simulations derived from experimental data, deviation of dark IV curves is due to flaws in the real device. These flaws are absent in simulation, but investigation verifies the characteristics of SCL current component's experimental IV curves within shunt leakage current. A device with a metal/CIGS/metal structure could simulate SCL current and confirm its characteristics. Such a simulated structure, representing flaws inserted into a CIGS solar cell, generates the same dark-current behavior revealed in experimental dark IV curves. This study investigates the response of dark current to varying sizes of the flaw within the CIGS solar cell. (C) 2013 Elsevier B.V. All rights reserved.
Breakthrough to Non-Vacuum Deposition of Single-Crystal, Ultra-Thin, Homogeneous Nanoparticle Layers: A Better Alternative to Chemical Bath Deposition and Atomic Layer Deposition
(2017-04-01)
Liao, Yu-Kuang
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Liu, Yung-Tsung
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Hsieh, Dan-Hua
;
Shen, Tien-Lin
;
Hsieh, Ming-Yang
Most thin-film techniques require a multiple vacuum process, and cannot produce high-coverage continuous thin filmswith the thickness of a fewnanometers on rough surfaces. We present a new "paradigm shift" non-vacuum process to deposit high-quality, ultra-thin, single-crystal layers of coalesced sulfide nanoparticles (NPs) with controllable thickness down to a few nanometers, based on thermal decomposition. This provides high-coverage, homogeneous thickness, and large-area deposition over a rough surface, with little material loss or liquid chemical waste, and deposition rates of 10 nm/min. This technique can potentially replace conventional thin-film deposition methods, such as atomic layer deposition (ALD) and chemical bath deposition (CBD) as used by the Cu(In, Ga) Se2 (CIGS) thin-film solar cell industry for decades. We demonstrate 32% improvement of CIGS thin-film solar cell efficiency in comparison to reference devices prepared by conventional CBD deposition method by depositing the ZnS NPs buffer layer using the new process. The new ZnS NPs layer allows reduction of an intrinsic ZnO layer, which can lead to severe shunt leakage in case of a CBD buffer layer. This leads to a 65% relative efficiency increase.
Crystalline Engineering Toward Large-Scale High-Efficiency Printable Cu(In,Ga)Se-2 Thin Film Solar Cells on Flexible Substrate by Femtosecond Laser Annealing Process
(2017-04-26)
Chen, Shih-Chen
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She, Nian-Zu
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Wu, Kaung-Hsiung
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Chen, Yu-Ze
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Lin, Wei-Sheng
Ink-printing method emerges as a viable way for manufacturing large-scale flexible Cu(In,Ga)Se-2 (CIGS) thin film photovoltaic (TFPV) devices owing to its potential for the rapid process, mass production, and low-cost nonvacuum device fabrication. Here, we brought the femtosecond laser annealing (fs-LA) process into the ink-printing CIGS thin film preparation. The effects of fs-LA treatment on the structural and optoelectronic properties of the ink-printing CIGS thin films were systematically investigated. It was observed that, while the film surface morphology remained essentially unchanged under superheating, the quality of crystallinity was significantly enhanced after the fs-LA treatment. Moreover, a better stoichiometric composition was achieved with an optimized laser scanning rate of the laser beam, presumably due to the much reduced indium segregation phenomena, which is believed to be beneficial in decreasing the defect states of In-se, V-Se, and In-cu. Consequently, the shunt leakage current and recombination centers were enhancement in photovoltaic conversion efficiency. both greatly decreased, resulting in a near 20%
Enhancing luminescence efficiency of InAs quantum dots at 1.5 mu m using a carrier blocking layer
(2006-07-31)
Hsieh, Tung-Po
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Chiu, Pei-Chin
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Chyi, Jen-Inn
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Chang, Hsiang-Szu
;
Chen, Wen-Yen
The authors report an effective way to enhance the optical efficiency of InAs quantum dots (QDs) on GaAs emitting at the wavelength of 1.5 mu m. It is found that the loss of holes from QDs to their proximity via the high indium composition InGaAs overgrown layer, which is necessary for achieving long wavelength emission, is the origin of photoluminescence intensity degradation at high temperature. Inserting a 4 nm thick Al0.45Ga0.55As layer, acting as a carrier blocking layer, into the GaAs capping matrix can improve the room temperature photoluminescence peak intensity by five and two times for the ground and first excited states, respectively.
Exciton fine structures and energy transfer in single InGaAs quantum-dot molecules
(2009)
Lin, Hsuan
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Wang, Sheng-Yun
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Lin, Chia-Hsien
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Chang, Wen-Hao
;
Cheng, Shun-Jen
We present a spectroscopic study of single quantum-dot molecules (QDMs) formed by two closely stacked In(0.5)Ga(0.5)As/GaAs layers. It was found that the interdot coupling and directional energy transfer between the two adjacent dots can be controlled by temperature tuning. Direct and indirect excitons, as well as charged excitons in single QDMs were classified and identified by excitation-power dependent, excitation-energy dependent and polarization-resolved microphotoluminescence measurements. With the increasing temperature, the direct-exciton intensity decreases while the indirect-exciton intensity increases. A rate equation model considering phonon mediated processes has been developed. The directional energy transfer in QDMs is explained in terms of the phonon-assisted tunnelling of hole between the two adjacent dots. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Highly Efficient Flexible Hybrid Nanocrystal-Cu(In,Ga)Se-2 (CIGS) Solar Cells
(2015-01-21)
Liao, Yu-Kuang
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Brossard, Mael
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Hsieh, Dan-Hua
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Lin, Tzu-Neng
;
Charlton, Martin D. B.
A novel scheme for hybridizing inkjet-printed thin film Cu(In,Ga)Se-2 (CIGS) solar cells with self-assembled clusters of nanocrystal quantum dots (NQDs), which provides a 10.9% relative enhancement of the photon conversion efficiency (PCE), is demonstrated. A non-uniform layer of NQD aggregates is deposited between the transparent conductive oxide and a CdS/CIGS p-n junction using low cost pulsed-spray deposition. Hybridization significantly improves the external quantum efficiency of the hybrid devices in the absorption range of the NQDs and in the red to near-IR parts of the spectrum. The low wavelength response enhancement is found to be induced by luminescent down-shifting (LDS) from the NQD layer, while the increase at longer wavelengths is attributed to internal scattering from NQD aggregates. LDS is demonstrated using time-resolved spectroscopy, and the morphology of the NQD layer is investigated in fluorescence microscopy and cross-sectional transmission electron microscopy. The influence of the NQD dose on the PCE of the hybrid devices is investigated and an optimum value is obtained. The low costs and limited material consumptions associated with pulsed-spray deposition make these flexible hybrid devices promising candidates to help push thin-film photovoltaic technology towards grid parity.
Low-density quantum dots embedded in photonic-crystal nanocavities for single-photon generations
(2007)
Chang, Wen-Hao
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Chen, Wen-Yen
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Chang, Hsiang-Szu
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Hsieh, Tung-Po
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Chyi, Jen-Inn
An efficient single-photon source based on low-density InGaAs quantum dots in a photonic-crystal nanocavity is demonstrated. The single-photon source features the effects of photonic band gap, yielding a single-mode spontaneous emission coupling efficiency as high as beta=92% and a linear polarization degree up to p=95%. This appealing performance makes it well-suited for practical implementation of polarization-encoded schemes in quantum cryptography.
Nonresonant carrier transfer in single InGaAs/GaAs quantum dot molecules
(2008-06-01)
Chang, Wen-Hao
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Lin, Hsuan
;
Wang, Sheng-Yun
;
Lin, Chia-Hsien
;
Cheng, Shun-Jen
We present a spectroscopic study of single quantum dot molecules (QDMs) formed by two closely stacked In(0.5)Ga(0.5)As layers. The exciton fine structures as well as direct and indirect excitonic species associated with QDMs were identified by power dependent and polarization resolved microphotoluminescence measurements. As the temperature was increased, a directional energy transfer between the direct and indirect excitons in single QDMs was observed. A rate-equation model was developed to explain our data. We show that a phonon-assisted nonresonant tunneling of the hole between the two adjacent dots is responsible for such directional energy transfers in QDMs.
Origins of nonzero multiple photon emission probability from single quantum dots embedded in photonic crystal nanocavities
(2009-04-20)
Chang, Hsiang-Szu
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Chen, Wen-Yen
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Hsu, Tzu-Min
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Hsieh, Tung-Po
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Chyi, Jen-Inn
This work explores the origins of nonzero multiphoton emission probability for quantum dots embedded in photonic crystal nanocavities using different excitation energies to inject excitons into either the GaAs barrier or the quantum-dot excited state. The detected multiphoton events are established to arise from both the recapture of excitons and background emissions from the wetting layer tail states. The exciton emission is analyzed using rate-equation calculations, which suggest that multiphoton emission is dominated by the recapture effect.
Single photon emission from an InGaAs quantum dot precisely positioned on a nanoplane
(2007-02-12)
Hsieh, Tung-Po
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Chyi, Jen-Inn
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Chang, Hsiang-Szu
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Chen, Wen-Yen
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Hsu, Tzu Min
This work demonstrates single photon emissions from a site-controlled quantum dot (QD) grown on a self-constructed nanoplane. The size of the nanoplane on the micron-sized multifacet structure is accurately controlled by a low surface reducing rate (similar to 16 nm/min). Single QD spectral lines were resolved and identified. The antibunching behavior reveals that single photons are emitted from the positioned QD. (c) 2007 American Institute of Physics.
Toward Omnidirectional Light Absorption by Plasmonic Effect for High-Efficiency Flexible Nonvacuum Cu(In,Ga)Se-2 Thin Film Solar Cells
(2014-09-01)
Chen, Shih-Chen
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Chen, Yi-Ju
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Chen, Wei Ting
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Yen, Yu-Ting
;
Kao, Tsung Sheng
We have successfully demonstrated a great advantage of plasmonic Au nanoparticles for efficient enhancement of Cu(In,Ga)Se-2(CIGS) flexible photovoltaic devices. The incorporation of Au NPs can eliminate obstacles in the way of developing ink-printing CIGS flexible thin film photovoltaics (TFPV), such as poor absorption at wavelengths in the high intensity region of solar spectrum, and that occurs significantly at large incident angle of solar irradiation. The enhancement of external quantum efficiency and photocurrent have been systematically analyzed via the calculated electromagnetic field distribution. Finally, the major benefits of the localized surface plasmon resonances (LSPR) in visible wavelength have been investigated by ultrabroadband pump-probe spectroscopy, providing a solid evidence on the strong absorption and reduction of surface recombination that increases electron hole generation and improves the carrier transportation in the vicinity of pn-juction.
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
;
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