Browsing by Author "Chou, Chun-Hsien"

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Controllable lasing performance in solution-processed organic-inorganic hybrid perovskites
(2016)
Kao, Tsung Sheng
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Chou, Yu-Hsun
;
Hong, Kuo-Bin
;
Huang, Jiong-Fu
;
Chou, Chun-Hsien
Solution-processed organic-inorganic perovskites are fascinating due to their remarkable photo-conversion efficiency and great potential in the cost-effective, versatile and large-scale manufacturing of opto-electronic devices. In this paper, we demonstrate that the perovskite nanocrystal sizes can be simply controlled by manipulating the precursor solution concentrations in a two-step sequential deposition process, thus achieving the feasible tunability of excitonic properties and lasing performance in hybrid metal-halide perovskites. The lasing threshold is at around 230 mu J cm(-2) in this solution-processed organic-inorganic lead-halide material, which is comparable to the colloidal quantum dot lasers. The efficient stimulated emission originates from the multiple random scattering provided by the micro-meter scale rugged morphology and polycrystalline grain boundaries. Thus the excitonic properties in perovskites exhibit high correlation with the formed morphology of the perovskite nanocrystals. Compared to the conventional lasers normally serving as a coherent light source, the perovskite random lasers are promising in making low-cost thin-film lasing devices for flexible and speckle-free imaging applications.
Flexible luminescent waveguiding photovoltaics exhibiting strong scattering effects from the dye aggregation
(2015-07-01)
Chou, Chun-Hsien
;
Hsu, Min-Hung
;
Chen, Fung-Chung
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光電工程學系
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Department of Photonics
Luminescent solar concentrators have received renewed interest because they can harvest solar radiation without the need for expensive tacking systems. In this work, highly efficient luminescent waveguiding photovoltaic devices exhibiting mechanical flexibility and solar concentration ability have been prepared by integrating Si solar cells with soft polydimethylsiloxane (PDMS) waveguides. We observed that segregated dyes in the PDMS waveguides induce strong scattering effects in the long-wavelength range. The scattered photons were transported effectively to the solar cells, leading to high power conversion efficiencies (PCEs). A single module exhibited a remarkable power conversion efficiency of 4.62 +/- 0.02%. After stacking two waveguides, we achieved PCEs as high as 5.23 +/- 0.01%, with a projected PCE approaching 12%. (C) 2015 Elsevier Ltd. All rights reserved.
High-Performance Flexible Waveguiding Photovoltaics
(2013-07-22)
Chou, Chun-Hsien
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Chuang, Jui-Kang
;
Chen, Fang-Chung
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光電學院
;
光電工程學系
The use of flat-plane solar concentrators is an effective approach toward collecting sunlight economically and without sun trackers. The optical concentrators are, however, usually made of rigid glass or plastics having limited flexibility, potentially restricting their applicability. In this communication, we describe flexible waveguiding photovoltaics (FWPVs) that exhibit high optical efficiencies and great mechanical flexibility. We constructed these FWPVs by integrating poly-Si solar cells, a soft polydimethylsiloxane (PDMS) waveguide, and a TiO2-doped backside reflector. Optical microstructures that increase the light harvesting ability of the FWPVs can be fabricated readily, through soft lithography, on the top surface of the PDMS waveguide. Our optimized structure displayed an optical efficiency of greater than 42% and a certified power conversion efficiency (PCE) of 5.57%, with a projected PCE as high as approximately 18%. This approach might open new avenues for the harvesting of solar energy at low cost with efficient, mechanically flexible photovoltaics.
Lasing behaviors upon phase transition in solution-processed perovskite thin films
(2014-12-08)
Kao, Tsung Sheng
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Chou, Yu-Hsun
;
Chou, Chun-Hsien
;
Chen, Fang-Chung
;
Lu, Tien-Chang
In this paper, the temperature dependent lasing characteristics of solution-processed organic-inorganic halide perovskite CH3NH3PbI3 films have been demonstrated. The lasing temperature can be sustained up to a near room temperature at 260 K. Via the temperature dependent photoluminescence (PL) measurements, an emerged phase-transition band can be observed, ascribing to the crystalline structures changed from the orthorhombic to tetragonal phase states in the perovskites as a function of a gradual increase in the ambient temperature. The optical characteristics of the PL emission peaks and the anomalous shifts of the peak intensities are highly correspondent with the phase states in perovskites at different temperatures, showing a low-threshold lasing behavior at the phase transition. The laser cavities may be formed under multiple random scattering provided by the polycrystalline grain boundary and/or phase separation upon the phase transition. Since the threshold gain is potentially high in the random cavities, the large material gain exhibited by the solution-processed perovskite would be very promising in making practical laser devices. (C) 2014 AIP Publishing LLC.
Plasmonic Effects on Bulk Heterojunction Polymer Solar Cells: A Transient Photovoltage and Differential Charging Study
(2017-08-01)
Kok, Soon Yie
;
Hsieh, Zong-Chun
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Chou, Chun-Hsien
;
Yang, Shun-Shing
;
Chuang, Ming-Kai
Transient photovoltage and differential charging experiments have been carried out to investigate the plasmonic effects in organic photovoltaic devices (OPVs). We observed that the carrier lifetimes became longer after the Au nanoparticles were blended into the OPVs. Additionally, the charge carrier densities also became higher in the bulk of the device. The carrier lifetime, however, usually follows an inverse power relationship with the increasing charge density in OPVs fabricated base on the concept of bulk heterojunctions. Therefore, we conclude that one of the limitations for the plasmonic approaches could be the strong bimolecular recombination.
Plasmonic nanostructures for light trapping in organic photovoltaic devices
(2014-08-07)
Chou, Chun-Hsien
;
Chen, Fang-Chung
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光電工程學系
;
顯示科技研究所
;
Department of Photonics
Over the past decade, we have witnessed rapid advances in the development of organic photovoltaic devices (OPVs). At present, the highest level of efficiency has surpassed 10%, suggesting that OPVs have great potential to become competitive with other thin-film solar technologies. Because plasmonic nanostructures are likely to further improve the efficiency of OPVs, this Article reviews recent progress in the development of metal nanostructures for triggering plasmonic effects in OPVs. First, we briefly describe the physical fundamentals of surface plasmons (SPs). Then, we discuss recent approaches toward increasing the light trapping efficiency of OPVs through the incorporation of plasmonic structures. Finally, we provide a brief outlook into the future use of SPs in highly efficient OPVs.