Browsing by Author "Hung, Chen-Shiung"

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Design and Characterization of Novel Porphyrins with Oligo(phenylethylnyl) Links of Varied Length for Dye-Sensitized Solar Cells: Synthesis and Optical, Electrochemical, and Photovoltaic Investigation
(2009-01-15)
Lin, Ching-Yao
;
Lo, Chen-Fu
;
Luo, Liyang
;
Lu, Hsueh-Pei
;
Hung, Chen-Shiung
Novel zinc porphyrins with 1-4 pi-conjugated phenylethyinyl (PE) units (labeled PE1-PE4) as a link of controlled length were synthesized for fundamental tests and applications as a dye-serisitized solar cell (DSSC). The UV-visible spectra of the solution samples show clear absorption patterns of the PE groups in a region 300-400 nm, consistent with results calculated with density-functional theory. Cyclic voltammograms of PE1-PE4 in tetrahydrofuran show similar electrochemical potentials for each compound. Ferntosecond fluorescence up-conversion of solution samples and of porphyrin-sensitized TiO(2) films was measured with excitation at 420 or 430 nm and emission at 460, 470, 620, and 680 nm. When these porphyrins were fabricated into DSSC devices, the efficiency of power conversion of these devices decreased systematically with increasing length of the link: 2.5 +/- 0.2% (PE1), 2.0 +/- 0.1% (PE2), 0.78 +/- 0.09% (PE3), 0.25 +/- 0.02% (PE4). This great photovoltaic degradation from PE1 to PE4 is not interpretable according to the rate of electron injection independent of length; other factors, including electron transfer from the semiconductor back to the porphyrin cation or the electrolyte, must be considered to account for the observed dependence of photovoltaic performance on length.
Effects of potential shift and efficiency of charge collection on nanotube-based porphyrin-sensitized solar cells with conjugated links of varied length
(2010)
Luo, Liyang
;
Lin, Chia-Jung
;
Hung, Chen-Shiung
;
Lo, Chen-Fu
;
Lin, Ching-Yao
For dye-sensitized solar-cell devices fabricated from porphyrin sensitizers with links of varied length (PE1-PE4) adsorbed on anodic titanium-oxide nanotube arrays, we measured induced photocurrent and photovoltage decays under constant bias illumination; the evaluated efficiencies of charge collection of the devices show a systematic trend PE4 > PE3 > PE2 > PE1 at a large short-circuit current, implying that a long link would improve the charge separation if the electrons were effectively injected into the semiconductor.
Fabrication and Characterization of Anodic Titanium Oxide Nanotube Arrays of Controlled Length for Highly Efficient Dye-Sensitized Solar Cells
(2008-12-04)
Chen, Chien-Chon
;
Chung, Hsien-Wen
;
Chen, Chin-Hsing
;
Lu, Hsuch-Pei
;
Lan, Chi-Ming
The performance of dye-sensitized solar cells (DSSC), made of highly ordered anodic titanium oxide (ATO) nanotube (NT) arrays produced directly on Ti foil, depends on the length of these arrays. We controlled these lengths L from 4 to 41 mu m while varying the concentration (0.1, 0.25, 0.5, and 0.8 wt %) of the electrolyte (NH(4)F) in ethylene glycol in the presence of H(2)O (2 vol %) with anodization for various periods (t = 0.5-8 h). The compact and bundle layers introduced. during anodization were effectively removed upon simple ultrasonic cleaning in deionized water containing submicrometer particles of Al(2)O(3) in a small proportion. The photovoltaic performance of the NT-DSSC devices (NH4F at 0.5 wt %) made of ATO films, as prepared, increased from 3.0% to 5.2% as L was increased from 6 mu m (t = 0.5 h) to 30 mu m (t = 8 h). After treatment of the ATO films with TiCl(4) in a two-step annealing process, the optimized NT-DSSC device attained an overall efficiency of 7.0% power conversion.
Femtosecond Transient Absorption of Zinc Porphyrins with Oligo(phenylethylnyl) Linkers in Solution and on TiO(2) Films
(2009-07-09)
Chang, Chih-Wei
;
Luo, Liyang
;
Chou, Chung-Kung
;
Lo, Chen-Fu
;
Lin, Ching-Yao
We measured femtosecond transient absorption of dye solutions and TiO(2) films sensitized with two zinc porphyrins (PE1 and PE4) to investigate the interfacial dynamics of electron transfer in relation to the dependence of cell performance on the length of the linker (Lin, C.-Y.; Lo, C.-F.; Luo, L.; Lu, H.-P.; Hung, C.-S.; Diau, E. W.-G. J. Phys. Chem. C 2009, 113, 755-764). For both porphyrins adsorbed on TiO(2) films with S(1) excitation (lambda(ex) = 620 nm), the transient absorption kinetics probed at 630 nm and 4.9 mu m are complementary to each other because only the excited-state and ground-state species were observed at 630 nm whereas only the charge-separation intermediates were observed at 4.9 mu m. The transient of the PE1/TiO(2) film shows a single exponential decay with a large offset, whereas the transient of the PE4/TiO(2) film displays a biexponential decay with a small offset. Because of the existence of an additional ps component, the amount of free delocalized electrons (offset signal) in PE4/TiO(2) is smaller than that in PEI/TiO(2). Our results imply that back electron transfer at the TiO(2)/dye interface is an important factor to be considered to account for the cell performance of a device.
Femtosecond Transient Absorption of Zinc Porphyrins with Oligo(phenylethylnyl) Linkers in Solution and on TiO2 Films
(2009-07-09)
Chang, Chih-Wei
;
Luo, Liyang
;
Chou, Chung-Kung
;
Lo, Chen-Fu
;
Lin, Ching-Yao
We measured femtosecond transient absorption of dye solutions and TiO2 films sensitized with two zinc porphyrins (PE1 and PE4) to investigate the interfacial dynamics of electron transfer in relation to the dependence of cell performance on the length of the linker (Lin, C.-Y.; Lo, C.-F.; Luo, L.; Lu, H.-P.; Hung, C.-S.; Diau, E. W.-G. J. Phys. Chem. C 2009, 113, 755-764). For both porphyrins adsorbed on TiO2 films with S-1 excitation (lambda(ex) = 620 nm), the transient absorption kinetics probed at 630 nm and 4.9 mu m are complementary to each other because only the excited-state and ground-state species were observed at 630 nm whereas only the charge-separation intermediates were observed at 4.9 mu m. The transient of the PE1/TiO2 film shows a single exponential decay with a large offset, whereas the transient of the PE4/TiO2 film displays a biexponential decay with a small offset. Because of the existence of an additional ps component, the amount of free delocalized electrons (offset signal) in PE4/TiO2 is smaller than that in PEI/TiO2. Our results imply that back electron transfer at the TiO2/dye interface is an important factor to be considered to account for the cell performance of a device.
Novel Steroid-Sensing Model and Characterization of Protein Interactions Based on Fluorescence Anisotropy Decay
(2010-04-01)
Chang, Ko-Shing
;
Luo, Liyang
;
Chang, Chih-Wei
;
Huang, Yen-Chieh
;
Cheng, Chih-Yu
Intramolecular binding of a ligand with an alkyl link, (-CH(2))(3), covalently bound to a residue near the active site of the protein forms a novel steroid-sensing model. A genetically engineered Delta(5)-3-ketosteroid isomerase (KSI) was designed to conjugate uniquely with this ligand at its Cys-86 through the formation of a disulfide bond. The steady-state protein-ligand binding, mediated by hydrophobic interactions, was confirmed with fluorescence spectra, and the fluorophore-labeled peptide sequence was identified with tandem mass spectra. A comparison of steady-state fluorescence spectra of various fluorophore-labeled KS1 mutants reveals that the emission characteristics vary with environmental factors. An evaluation of the decay of the fluorescence anisotropy of the fluorophore indicates the existence of an intramolecular protein-ligand binding interaction. The measurement of time-resolved fluorescence anisotropy of various protein-ligand complexes yielded values of anisotropy decay representing the degrees of freedom of the fluorophore related to its location, inside or Outside the steroid-binding domain. When 19-norandrostenedione (19-NA) was added to this protein-ligand system, competitive binding between the ligand and the steroid was observed; this finding confirms the feasibility of the design of steroid detection with engineered KSI. On integration of this protein-ligand system with a silicon-based nanodevice (a p-type field-effect transistor with an Ultrathin body), it noncharged steroid, 19-NA, became detectable at it micromolar level (Biosens. Bioelectron. 2008, 23, 1883).