Browsing by Author "Lin, Zhan-Hong"

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Design of novel TiO2-SiO2 core-shell helical nanostructured anti-reflective coatings on Cu(In,Ga)Se-2 solar cells with enhanced power conversion efficiency
(2019-05-14)
Chen, Chia-Wei
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Tsai, Hung-Wei
;
Wang, Yi-Chung
;
Su, Teng-Yu
;
Yang, Chen-Hua
Introducing an anti-reflective coating (ARC) is the last step of fabricating Cu(In,Ga)Se-2 solar cells with enhanced photo-generated current by reducing the reflectance of visible light. The use of nanostructures in ARC has been intensively investigated because this can prolong the optical path length by a scattering effect or by the formation of a refractive index gradient. Herein, we proposed the use of TiO2 helical nanostructures using glancing angle deposition (GLAD), and then synthesized SiO2 surrounding the helical nanostructures to further decrease the reflectance by producing a refractive index gradient. The optimized values of TiO2 and SiO2 thicknesses are 150 nm and 3 nm determined by the finite-difference time-domain (FDTD) simulation on Cu(In,Ga)Se-2 solar cells. The suppression of reflectance led to enhanced light absorption across a broad wavelength range, and boosted the J(SC) from 20.66 to 22.51 mA cm(-2), resulting in improved power conversion efficiency (PCE) from 6.32 to 7.00% after applying the TiO2-SiO2 core-shell nanostructures as the ARC. This 10.75% PCE enhancement suggests that the novel TiO2-SiO2 core-shell nanostructures have great potential as ARC for Cu(In,Ga)Se-2 solar cells, and it would be beneficial for development in the photovoltaic field in both research and applications.
Generation of optical chirality patterns with plane waves, evanescent waves and surface plasmon waves
(2020-01-06)
Zhang, Jiwei
;
Huang, Shiang-Yu
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Lin, Zhan-Hong
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Huang, Jer-Shing
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電子物理學系
We systematically investigate the generation of optical chirality patterns by applying the superposition of two waves in three scenarios, namely free-space plane waves, evanescent waves of totally reflected light at dielectric interface and propagating surface plasmon waves on a metallic surface. In each scenario, the general analytical solution of the optical chirality pattern is derived for different polarization states and propagating directions of the two waves. The analytical solutions are verified by numerical simulations. Spatially structured optical chirality patterns can be generated in all scenarios if the incident polarization states and propagation directions are correctly chosen. Optical chirality enhancement can be obtained from the constructive interference of free-space circularly polarized light or enhanced evanescent waves of totally reflected light. Surface plasmon waves do not provide enhanced optical chirality unless the near-field intensity enhancement is sufficiently high. The structured optical chirality patterns may find applications in chirality sorting, chiral imaging and circular dichroism spectroscopy. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Optical microresonator arrays of fluorescence-switchable diarylethenes with unreplicable spectral fingerprints
(2020-07-01)
Okada, Daichi
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Lin, Zhan-Hong
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Huang, Jer-Shing
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Oki, Osamu
;
Morimoto, Masakazu
High-security identification requires authentication that is hard to counterfeit and replicate. For anti-counterfeiting data storage and rewritable memory devices, chromic materials are adoptable, where the dichromatic colours can be switched by external stimuli. If further individual information is embedded in each pixel, a much higher-level security system beyond the zero/one data array will be realized. For this purpose, a fine whispering gallery mode (WGM) fingerprint pattern from a microresonator is applicable. Here we propose that photoswitchable optical microresonators made of a fluorescent photochromic organic material function as anti-counterfeiting, rewritable optical memories. The WGM photoluminescence of the resultant microspheres can be switched on and off repeatedly by irradiation with ultraviolet and visible light. The shape of the micro-resonator varies from a sphere to an oblate ellipsoid and hemisphere, depending on the self-assembly process, and the WGM spectral pattern depends sensitively on the morphology of the resonators. Furthermore, surface self-assembly on a hydrophobic/hydrophilic micropatterned substrate affords a highly integrated array of microresonators as dense as millions of pixels per square centimetre. The spectral fingerprints of all pixels are different from one another; therefore, the photoswitchable microarrays are applicable as an ultimate anti-counterfeiting system which is hard to replicate.
Stress-Induced 3D Chiral Fractal Metasurface for Enhanced and Stabilized Broadband Near-Field Optical Chirality
(2019-08-01)
Tseng, Ming Lun
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Lin, Zhan-Hong
;
Kuo, Hsin Yu
;
Huang, Tzu-Ting
;
Huang, Yi-Teng
Metasurfaces comprising 3D chiral structures have shown great potential in chiroptical applications such as chiral optical components and sensing. So far, the main challenges lie in the nanofabrication and the limited operational bandwidth. Homogeneous and localized broadband near-field optical chirality enhancement has not been achieved. Here, an effective nanofabrication method to create a 3D chiral metasurface with far- and near-field broadband chiroptical properties is demonstrated. A focused ion beam is used to cut and stretch nanowires into 3D Archimedean spirals from stacked films. The 3D Archimedean spiral is a self-similar chiral fractal structure sensitive to the chirality of light. The spiral exhibits far- and near-field broadband chiroptical responses from 2 to 8 mu m. With circularly polarized light (CPL), the spiral shows superior far-field transmission dissymmetry and handedness-dependent near-field localization. With linearly polarized excitation, homogeneous and highly enhanced broadband near-field optical chirality is generated at a stably localized position inside the spiral. The effective yet straightforward fabrication strategy allows easy fabrication of 3D chiral structures with superior broadband far-field chiroptical response as well as strongly enhanced and stably localized broadband near-field optical chirality. The reported method and chiral metasurface may find applications in broadband chiral optics and chiral sensing.