Browsing by Author "Ke, L."

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    A complementary electrochromic device with highly improved performance based on brick-like hydrated tungsten trioxide film
    (American Scientific Publishers, 2012) Jiao, Z.; Wang, J.; Ke, L.; Sun, X. W.; Demir, Hilmi Volkan
    Uniform and well adhesive nanostructured hydrated tungsten trioxide (3WO 3•H 2O) films were grown on fluorine doped tin oxide (FTO) substrate via a facile and template-free crystal-seed-assisted hydrothermal method by addition of ammonium sulfate ((NH 4) 2SO 4) and hydrogen peroxide (H 2O 2). X-ray diffraction (XRD) studies indicated that the films are of orthorhombic structure. Scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) analysis showed that the film was composed of brick-like nanostructures with a preferred growing direction along (002). The influence of seed layer, (NH 4) 2SO 4 and H 2O 2 on the products were also studied. The film showed good cyclic stability, comparable switching speed and coloration efficiency (30.1 cm 2 C -1). A complementary electrochromic device based on the film and Prussian blue depicted highly improved color contrast, coloration/bleaching response (1.8 and 3.7 s respectively) and coloration efficiency (164.6 cm 2 C -1).
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    Dye-sensitized solar cell with a pairof carbon-based electrodes
    (IOP Publishing, 2012-04-02) Kyaw, A. K. K.; Tantang, H.; Wu, T.; Ke, L.; Wei, J.; Demir, Hilmi Volkan; Zhang, Q.; Sun, X. W.
    We have fabricated a dye-sensitized solar cell (DSSC) with a pair of carbon-based electrodes using a transparent, conductive carbon nanotubes (CNTs) film modified with ultra-thin titanium-sub-oxide (TiOx) as the working electrode and a bilayer of conductive CNTs and carbon black as the counter electrode. Without TiOx modification, the DSSC is almost nonfunctional whereas the power conversion efficiency (PCE) increases significantly when the working electrode is modified with TiOx. The performance of the cell could be further improved when the carbon black film was added on the counter electrode. The improved efficiency can be attributed to the inhibition of the mass recombination at the working electrode/electrolyte interface by TiOx and the acceleration of the electron transfer kinetics at the counter electrode by carbon black. The DSSC with a pair of carbon-based electrodes gives the PCE of 1.37%.
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    Dye-sensitized solar cell with a titanium-oxide-modified carbon nanotube transparent electrode
    (American Institute of Physics, 2011-07-15) Kyaw, A. K. K.; Tantang, H.; Wu, T.; Ke, L.; Peh, C.; Huang, Z. H.; Zeng, X. T.; Demir, Hilmi Volkan; Zhang, Q.; Sun, X. W.
    Transparent and conductive carbon-based materials are promising for window electrodes in solid-state optoelectronic devices. However, the catalytic activity to redox reaction limits their application as a working electrode in a liquid-type dye-sensitized solar cell (DSSC). In this letter, we propose and demonstrate a transparent carbon nanotubes (CNTs) film as the working electrode in a DSSC containing iodide/triiodide redox couples. This implementation is realized by inhibiting the charge-transfer kinetics at CNT/redox solution interface with an aid of thin titanium oxide film that facilitates the unidirectional flow of electrons in the cell without sacrificing the electrical and optical properties of CNT.
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    Efficient synthesis of plate-like crystalline hydrated tungsten trioxide thin films with highly improved electrochromic performance
    (Royal Society of Chemistry, 2011) Jiao, Z.; Wang, X.; Wang, J.; Ke, L.; Demir, Hilmi Volkan; Koh, T. W.; Sun, X. W.
    Plate-like hydrated tungsten trioxide (3WO(3)center dot H(2)O) films were grown on a fluorine doped tin oxide (FTO) coated transparent conductive substrate via an efficient, facile and template-free hydrothermal method. The film exhibited a fast coloration/bleaching response (t(c90%) = 4.3 s and t(b90%) = 1.4 s) and a high coloration efficiency (112.7 cm(2) C(-1)), which were probably due to a large surface area.
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    Electrochromic properties of nanostructured tungsten trioxide (hydrate) films and their applications in a complementary electrochromic device
    (Elsevier, 2011-12-26) Jiao, Z.; Wang, J.; Ke, L.; Liu, X.; Demir, Hilmi Volkan; Yang, M. F.; Sun, X. W.
    Orthorhombic hydrated tungsten trioxide (3WO(3)center dot H2O) films consisted of nanosticks and nanoparticles were prepared on fluorine doped tin oxide (FTO)-coated substrate by a facile and template-free hydrothermal method using ammonium acetate (CH3COONH4) as the capping agent. Irregular nanobrick films were obtained without capping agent. Due to the highly rough surface, the nanostick/nanoparticle film depicts faster ion intercalation/deintercalation kinetics and a greater coloration efficiency (45.5 cm(2)/C) than the nanobrick film. A complementary electrochromic device based on the nanostick/nanoparticle 3WO(3)-H2O film and Prussian blue (PB) was assembled. As a result, the complementary device shows a higher optical modulation (54% at 754 nm), a larger coloration efficiency (151.9 cm(2)/C) and faster switching responses with a bleaching time of 5.7 s and a coloring time of 1.3 s than a single 3WO(3).H2O layer device, making it attractive for a practical application.
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    A fast-switching light-writable and electric-erasable negative photoelectrochromic cell based on Prussian blue films
    (Elsevier, 2011) Jiao, Z.; Song, J. L.; Sun, X. W.; Liu, X. W.; Wang, J. M.; Ke, L.; Demir, Hilmi Volkan
    We report a fast-switching negative photoelectrochromic cell composed of a dye-sensitized nanocrystalline TiO2 electrode and Prussian blue counter electrode sandwiching a LiI electrolyte. The cell can be bleached under illumination with shorted TiO2 and Prussian blue electrodes, and re-colored by applying an appropriate external voltage. The photo-bleaching and electric-coloring processes are fast and reversible. A maximum absorbance modulation of 0.44 recorded at 700 nm is obtained between bleached and colored states for the cell when the PB film's thickness is 452 nm. Illuminated under different levels of light intensity or durations of time, the shorted cell shows adjustable optical absorption from 470 to 840 nm. The in-situ transmittance response depicts that the photo-bleaching response is 6.2 s for 70% transmittance change under 100 mW/cm(2) illumination in short circuit configuration, and the re-coloration time is about 600 ms under 2 V bias recorded at 780 nm, with an electrochromic coloration efficiency of 103.4 cm(2)/C. The cell shows a good reversible stability and can be potentially applied in erasable displays.
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    Morphology-tailored synthesis of tungsten trioxide (Hydrate) thin films and their photocatalytic properties
    (ACS Publications, 2011-01-10) Jiao, Z. H.; Wang, J. M.; Ke, L.; Sun, X. W.; Demir, Hilmi Volkan
    Tungsten trioxide hydrate (3WO(3)center dot H(2)O) films with different morphologies were directly grown on fluorine doped tin oxide (FTO) subsi:rate via a facile crystal-seed-assisted hydrothermal method. Scanning electron microscopy (SEM) analysis showed that 3WO(3)center dot H(2)O thin films composed of platelike, wedgelike, and sheetlike nanostructures could be selectively synthesized by adding Na(2)SO(4), (NH(4))(2)SO(4), and CH(3)COONH(4) as capping agents, respectively. X-ray diffraction (XRD) studies indicated that these films were of orthorhombic structure. The as-prepared thin films after dehydration showed obvious photcicatalytic activities. The best film grown using CH(3)COONH(4) as a capping agent generated anodic photocurrents of 1.16 mA/cm(2) fork oxidization of methanol and 0.5 mA/cm(2) for water splitting with the highest photoconversion efficiency of about 0.3% under simulated solar illumination.
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    Solution Processed Tungsten Oxide Interfacial Layer for Efficient Hole-Injection in Quantum Dot Light-Emitting Diodes
    (Wiley-VCH Verlag, 2014) Yang, X.; Mutlugun, E.; Zhao, Y.; Gao, Y.; Leck, K. S.; Ma, Y.; Ke, L.; Tan, S. T.; Demir, Hilmi Volkan; Sun, X. W.
    A highly efficient and stable QLED using an inorganic WO3 nanoparticle film as a hole injection layer is demonstrated.The resulting WO3 nanoparticle-based QLEDs also exhibit superior performance compared to that of the present PEDOT:PSS-based QLEDs. The results indicate that WO3 nanoparticles are promising solution-processed buffer layer materials and serve as a strong candidate for QLED technology towards the practical applications in the next-generation lighting and displays. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.