Showing papers by "Kuo-Chuan Ho published in 2010"

Molecularly Imprinted Electrochemical Sensors

Abstract: In this review, the applications of molecularly imprinted polymer (MIP) materials in the area of electrochemical sensors have been explored. The designs of the MIPs containing different polymers, their preparation and their immobilization on the transducer surface have been discussed. Further, the employment of various transducers containing the MIPs based on different electrochemical techniques for determining analytes has been assessed. In addition, the general protocols for getting the electrochemical signal based on the binding ability of analyte with the MIPs have been given. The review ends with describing scope and limitations of the above electrochemical based MIP sensors.

A high performance dye-sensitized solar cell with a novel nanocomposite film of PtNP/MWCNT on the counter electrode

Abstract: An imide-functionalized material, poly(oxyethylene)-segmented polymer, was synthesized from the reaction of poly(oxyethylene)diamine of 2000 g mol−1Mw and 4,4′-oxydiphthalic anhydride and used to disperse hybrid nanomaterials of platinum nanoparticles and multi-wall carbon nanotubes (PtNP/MWCNT). The composite material was spin-coated into film and further prepared as the counter electrode (PtNP/MWCNT-CE) for a dye-sensitized solar cell (DSSC). The short-circuit current density (JSC) and power-conversion efficiency (η) of the DSSC with PtNP/MWCNT-CE were found to be 18.01 ± 0.91 mA cm−2 and 8.00 ± 0.23%, respectively, while the corresponding values were 14.62 ± 0.19 mA cm−2 and 6.92 ± 0.07% for a DSSC with a bare platinum counter electrode (Pt-CE). The presence and distribution of PtNP/MWCNT on the CE were characterized by using scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The attachment of PtNPs on MWCNTs was observed by transmission electron microscopy (TEM). Cyclic voltammetry (CV), incident-photo-to-current efficiency (IPCE) and electrochemical impedance spectra (EIS) were correlated to explain the efficacy of this nanocomposite system.

Iodine-free high efficient quasi solid-state dye-sensitized solar cell containing ionic liquid and polyaniline-loaded carbon black

Abstract: An incombustible and non-volatile paste with carbon black (CB), a conducting polymer (CP), and an ionic liquid (1-buty-3-methylimidazolium iodide, BMII or 1-methyl-3-propyl imidazolium iodide, PMII) was placed between the dye-sensitized porous TiO2 and the Pt counter electrode to fabricate a quasi solid-state DSSC, without the addition of iodine. While the solar-to-electricity efficiencies (η) were measured to be 4.38% and 3.68% for the cells with PMII/CB and BMII/CB, respectively, the corresponding values without CB were 0.6% and 0.3%; indicating the remarkable role played by the carbon material in the electrolyte. When the CB was replaced with polyaniline-loaded carbon black (PACB), an efficiency of 5.81% was obtained, at 100 mW cm−2 AM1.5 illumination using PMII, the highest ever reported for a quasi solid-state DSSC made without iodine. High thermal stability up to 250 °C for each component in the composite electrolytes was confirmed by thermogravimetric analyses (TGA). At-rest durability of the DSSC with PACB was studied both at room temperature and at 70 °C and was found to be far superior to that of a cell with an organic solvent electrolyte. Electrochemical impedance spectroscopy (EIS) and dark current measurements were used to substantiate the results.

A ternary cascade structure enhances the efficiency of polymer solar cells

Abstract: In this study, a novel solution-processed small molecule (TQTFA) for use as an electron donor has been incorporated into organic solar cells based on poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl C71-butyric acid methyl (PC[70]BM). The combination of TQTFA with P3HT and PC[70]BM allows not only a broad absorption but also tuning of the inter energy level leading to a higher short-circuit current (JSC) and open-circuit voltage (VOC). The best performing devices exhibited a power conversion efficiency of 4.50%. The efficiency is increased by almost 15% when compared to the one without TQTFA.

Fabrication of NOx gas sensors using In2O3-ZnO composite films

Abstract: In 2 O 3 –ZnO composite films were fabricated and their NO x sensing characteristics were investigated in this study. The content of ZnO in In 2 O 3 –ZnO film was controlled by adjusting the Zn 2+ /In 3+ molar ratio ( r ) during the film preparation. With suitable amount of ZnO incorporated into the In 2 O 3 films, the responses of the composite films to NO x at operation temperatures below 200 °C were greatly improved. However, as the ZnO content was further increased, the grain of the composite film started to merge into big ones, thus decreasing the surface area and resulting in lower sensor responses. The detection limit ( S / N = 3) of In 2 O 3 –ZnO composite film ( r = 0.67) reached 12 ppb at 150 °C. Both pure In 2 O 3 ( r = 0) and In 2 O 3 –ZnO composite films ( r = 0.67) showed no response to CO gas.

Fabrication of a ZnO film with a mosaic structure for a high efficient dye-sensitized solar cell

Abstract: A flexible photoanode with zinc oxide film on titanium foil was prepared and its application in a dye-sensitized solar cell (DSSC) was investigated. The ZnO film with a mosaic structure, composed of densely packed ZnO nanosheets (ZnONS), was obtained by calcining a film of layered hydroxide zinc carbonate (LHZC), which was previously grown directly on a Ti foil via chemical bath deposition (CBD). The highly porous ZnONS film with a film thickness of about 25 μm could be facilely prepared within 4 h under CBD conditions. Owing to the intrinsic properties of the ZnONS film, i.e., high porosity, high surface area, and effective electron transport, a solar-to-electricity conversion efficiency (η) of 5.41% was achieved for the pertinent back-illuminated DSSC, which is the highest ever reported value for a back-illuminated DSSC based on a ZnO photoanode. The effect of the sputtering time of platinum (Pt) and iodine concentration on the photovoltaic performance of the DSSC were also investigated. Films on the substrates were characterized by X-ray diffraction (XRD) patterns, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Transmission spectra were obtained to characterize Pt films. Electrochemical impedance spectra (EIS) were obtained to analyze the charge transfer resistance and Warburg diffusion process in the DSSCs. Incident photon-to-current conversion efficiency (IPCE) curves were used to support the behavior of short-circuit photocurrent (JSC) of DSSCs and also to calculate its values. Electron lifetimes in photoanodes were determined using Bode-phase plots.

Detection of uric acid based on multi-walled carbon nanotubes polymerized with a layer of molecularly imprinted PMAA

Abstract: A molecularly imprinted poly-methacrylic acid (PMAA), polymerizing on the surface of multi-walled carbon nanotubes (MWCNTs), was synthesized. The MWCNTs were modified by a layer of carboxylic acid and reacted with 1-ethyl-3-(3-dimethylamino-propyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) to activate the carboxylic acid, which was prepared for the purpose of bonding allyl amine and getting an unsaturated side chain (–CH CH 2 ). The molecularly imprinted polymers (MIPs) based on PMAA were polymerized on the surface of MWCNTs–CH CH 2 with the addition of uric acid (UA). The non-imprinted polymers (NIPs) were polymerized without adding UA. The adsorbed amount of UA approached the equilibrium value upon 10 min adsorption. The adsorption isotherms suggest that the MIP particles adsorb higher amount of UA than that of NIP particles and possess a good imprinting efficiency of about 4.41. The adsorption isotherms were correlated successfully by the Freundlich model and the micro-pore adsorption behavior was considered. Amperometric detection also declared similar aspect than the adsorption results and shows high selective property due to the electro-active ascorbic acid (AA).

All-solid-state dye-sensitized solar cells incorporating SWCNTs and crystal growth inhibitor

Abstract: A solid organic ionic crystal, 1-ethyl-3-methylimidazolium iodide (EMII), was employed as a charge transfer intermediate (CTI) to fabricate all-solid-state dye-sensitized solar cells (DSSCs). In addition, single wall carbon nanotubes (SWCNTs) were incorporated into the CTI as the extended electron transfer materials (EETM), which can reduce charge diffusion length and serve simultaneously as catalyst for the electrochemical reduction of I3−. An all-solid-state DSSC with this hybrid SWCNT-EMII achieved a higher cell efficiency (1.88%), as compared to that containing bare EMII (0.41%). To further improve the cell efficiency, we utilized 1-methyl-3-propylimidazolium iodine (PMII), which acts simultaneously as a co-charge transfer intermediate and crystal growth inhibitor. The binary CTI (EMII mix with PMII) is in the form of solid as the weight percentage of PMII reaches 60%, at which a smoother surface morphology for the binary CTI is observed. The highest cell efficiency (3.49%) was obtained using a hybrid SWCNT-binary CTI. At-rest durability of the DSSC with the hybrid SWCNT-binary CTI was also studied and found to be far superior to that of a cell with an organic solvent electrolyte. Electrochemical impedance spectroscopy (EIS) and laser-induced photo-voltage transient were used to substantiate the results.

The Influence of Charge Trapping on the Electrochromic Performance of Poly(3,4-alkylenedioxythiophene) Derivatives

Abstract: This paper describes the electrochromic properties of a series of poly(3,4-alkylenedioxythiophene) (PXDOT) derivatives featuring various ring sizes and substitutions. The presence of a bulky group on the monomer resulted in a polymer possessing a more-open morphology, which promoted reversible ionic transfer. We used an electrochemical quartz crystal microbalance and cyclic voltammetry to investigate the properties of these polymers. We found that both cations and anions were involved in the charge compensation process. Furthermore, PXDOT derivatives possessing larger ring sizes and/or longer alkyl substituents exhibited less trapping of ions within the polymer during the redox process. The long-term electrochromic stability of these PXDOTs depended strongly on the number of trapped ions. Although the transmittance attenuation of poly(3,4-ethylenedioxythiophene) (PEDOT) decreased from 53 to 42%, we observed no significant decay for poly(diethyl-3,4-dihydro-2H-thieno[3,4-b]-[1,4]dioxepine) (PProDOT-Et2) af...

An efficient flexible dye-sensitized solar cell with a photoanode consisting of TiO2 nanoparticle-filled and SrO-coated TiO2 nanotube arrays

Abstract: Three types of flexible dye-sensitized solar cells (DSSC) were fabricated, using as the photoanode an array of TiO2 nanotubes (TNT) or TiO2 nanotubes filled with TiO2 nanoparticles (TNT-TNP, particle size 14 nm) or TiO2 nanotubes not only filled with nanoparticles but also coated with a layer of strontium oxide (TNT-TNP-SrO). The nanotubes were obtained by electrochemical oxidation of a Ti sheet and their lengths (0.5 μm to 18.8 μm) were controlled by varying the anodization period from 0.25 to 18 h. The DSSC using titanium nanotube arrays as the photoanode (hereafter called TNT-DSSC) showed a solar-to-electricity conversion efficiency (η) of 3.46%, when the anodization period was 12 h. When TNT-TNP was used as the anode, the efficiency of the DSSC (hereafter called TNT-TNP-DSSC) has increased to 4.56%. An efficiency of 5.39% was obtained when TNT-TNP-SrO was used as the photoanode for the DSSC (hereafter called TNT-TNP-SrO-DSSC). Our own dye, coded as CYC-B1 was used in all the cases. The morphologies of TNT and TNT-TNP were characterized by FE-SEM. XRD was used to characterize the TNT. Explanations on the photovoltaic performances of the DSSCs are substantiated by using electrochemical impedance spectra (EIS), incident photon to current conversion efficiency (IPCE) curves, and Mott-Schottky plots.

Using a low temperature crystallization process to prepare anatase TiO2 buffer layers for air-stable inverted polymer solar cells

Abstract: In this study, we fabricated inverted polymer solar cells featuring titanium dioxide (TiO2) as the electron collection layer and vanadium (V) oxide (V2O5) as the hole collection layer. TiO2 films (anatase phase) were prepared by combining electrochemical deposition with high-pressure crystallization. The low temperature process used to obtain the TiO2 films minimized interdiffusion of Ti and In species between the TiO2 and ITO films and maintained the conductivity of the indium tin oxide substrate. The inverted device reached a power conversion efficiency of 3.22% and exhibited much better stability under ambient conditions relative to that of the corresponding conventional device.

Heteroleptic ruthenium antenna-dye for high-voltage dye-sensitized solar cells

Abstract: A new ruthenium photosensitizer, coded CYC-B7, incorporating a bithienyl-carbazole antenna ligand was designed and prepared for improving the open-circuit voltage (Voc) of a dye-sensitized solar cell (DSC) device. This new sensitizer displays the low energy MLCT transition band centered at 551 nm with a high molar absorption coefficient of 2.19 × 104 M−1 cm−1. In addition, a simple approach to reduce the aggregation of bulky ruthenium dyes assembled onto the surface of TiO2 film is demonstrated. The cell based on this new heteroleptic ruthenium dye provides a high Voc of 788 mV and an overall conversion efficiency (η) of 8.96%. The functionality of carbazole in CYC-B7 resulting in the increases of the Voc value of the corresponding device is verified by comparing with the performance of the DSC sensitized with a structurally similar dye without carbazole.

Efficient bilayer polymer solar cells possessing planar mixed-heterojunction structures

Abstract: We have investigated the influence of thermal annealing on the performance of polymer bilayer solar cell devices incorporating poly{2,6-(4,4-bis[2-ethylhexyl]-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)} (PCPDTTBT) as the donor and two kinds of fullerenes (C60, C70) as acceptors. The higher absorption of C70 increased the external quantum efficiency in the spectral range 400–600 nm. We observed morphological changes of the polymer films when the pre-annealing temperature was near the crystalline temperature (Tc, 207 °C). These nanostructural transformations resulted in a modified interfacial morphology of the donor phases and, therefore, greatly influenced the device performance. Post-annealing treatment reorganized the interface between the donor and acceptor phases, leading to better contact. The highest power conversion efficiency (2.85%) was obtained when we performed device pre- and post-annealing both at 200 °C for 30 min; the open-circuit voltage was 0.69 V and the short-circuit current was 8.42 mA cm−2.

Modulation of Donor-Acceptor Interface through Thermal Treatment for Efficient Bilayer Organic Solar Cells

Abstract: In this article, we demonstrate the effect of donor−acceptor (D-A) interface on the performance of bilayer organic solar cells. Solution processing was used to develop liquid crystal poly(9,9′-dioctylfluorene-co-bithiophene) (F8T2) polymer films and variable morphology of the films was achieved by varying the annealing temperature. The morphology of the annealed active layers signature a well-aligned nanodomain feature with an interdegitated structure at 200 °C. The devices with bilayer configuration, ITO/PEDOT:PSS/F8T2/C70/Al, have yielded a power conversion efficiency (PCE) of 3.4(±0.2)% under 1 sun incident radiation. We attribute the high PCE to the increased D-A junction interface and balanced charge transport between electron/hole transport layers.

Monitoring the 3D nanostructures of bulk heterojunction polymer solar cells using confocal lifetime imaging.

Abstract: In this study, the exciton lifetime images within the photoactive layers of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are revealed by confocal optical microscopy combined with the fluorescence module. The images reveal that the active layers during slow solvent evaporation provide 3D pathways for charge transport and the concentration gradient through the film which reflects the better cell performance. This technique offers a great help to investigate the 3D optical-physical property without destroying the blends.

Toward Optimization of Oligothiophene Antennas: New Ruthenium Sensitizers with Excellent Performance for Dye-Sensitized Solar Cells

Abstract: This paper reports on the design and synthesis of three new ruthenium sensitizers, as well as the optimization of their linear or dendritic light-harvesting oligothiophene antennas to achieve superior device performance. The three new ruthenium sensitizers, [Ru(dcbpy)(obtip)(NCS)2] (JF-5, dcbpy =4,4′-dicarboxylic acid-2,2′-bipyridine, obtip =2-(5-octyl-(2,2′-bithiophen)-5′-yl)-1H-imidazo[4,5-f][1,10]phenanthroline), [Ru(dcbpy)(ottip)(NCS)2] (JF-6, ottip =2-(5-octyl-2,2′,5′,2′′-terthiophen)-5′′-yl)-1H-imidazo[4,5-f][1,10]phenanthroline), and [Ru(dcbpy)(dottip)(NCS)2] (JF-7, dottip =2-(2,3-di-(5-octylthiophen-2-yl)thiophen-5-yl)-1H-imidazo[4,5-f][1,10]phenanthroline), were synthesized in a typical one-pot reaction. The ruthenium sensitizer JF-5 incorporating a linear and planar 2,2′-bithiophene antenna showed the best DSCs performance (9.5%; compared to N3, 8.8%). The difference in the performance of these sensitizers demonstrates that elongating the linear and planar light-harvesting antenna result in an e...

A High Contrast Hybrid Electrochromic Device Containing PEDOT, Heptyl Viologen, and Radical Provider TEMPO

Abstract: An anodic radical provider, 2,2,6,6-tetramethyl-1-piperidinyloxy TEMPO, and two electrochromic EC materials, poly3,4ethylenedioxythiophenePEDOT and heptyl viologen HVBF42, were utilized to fabricate a hybrid electrochromic device ECD. PEDOT and HVBF42 were used as film and solution-type cathodic EC materials, respectively. The ECD exhibited two-stage redox reactions with high absorbance attenuation in the visible region. With the variation in the operating voltage, a maximum transmittance change T of 20% at 610 nm was observed in the first stage 0.5 to 0.8 V, whereas a maximum T of 68% was observed in the second stage 0.8‐1.5 V. Furthermore, fast switching times of 6.9 and 2.1 s were estimated for bleaching and darkening, respectively. The coloration efficiencies at 610 nm were 171.9 and 91.0 cm 2 C