Showing papers by "Kuo-Chuan Ho published in 2008"

2,3-Disubstituted Thiophene-Based Organic Dyes for Solar Cells

Abstract: New organic dyes that contain variable lengths of conjugation, featuring oligothiophene and arylamines at the 2- and 3-position, have been synthesized. These compounds are characterized by photophysical, electrochemical, and theoretical computational methods. Nanocrystalline TiO2-based dye-sensitized solar cells were fabricated using these molecules as light-harvesting sensitizers. The overall efficiencies of the sensitized cells range from 4.11 to 6.15%, compared to a cis-di(thiocyanato)-bis(2,2′-bipyridyl)-4,4′-dicarboxylate ruthenium(II)-sensitized device (7.86%) fabricated and measured under similar conditions. The devices made from these compounds have higher open-circuit voltage (VOC) compared to oligothiophene congeners with arylamines at the 2-position only. The hydrophobic segment at the 3-position appears to help retarding the charge transfer from the conduction band of TiO2 to the electrolyte, I3−. Supplementary studies of the transient photovoltage and electrochemical impedance are in support ...

Complementary inverter circuits based on p-SnO2 and n-In2O3 thin film transistors

Abstract: Thin film transistors (TFTs) of indium oxide (In2O3) and tin oxide (SnO2) were fabricated on SiO2 gate dielectric using reactive evaporation process. Structural investigation of the films revealed that In2O3 films were polycrystalline in nature with preferred (222) orientation and SnO2 films exhibited amorphous nature. The x-ray photoelectric spectroscopy measurements suggest that SnO2 films were oxygen rich and presume mixed oxidation states of Sn, namely Sn2+ and Sn4+. While the In2O3 based TFTs possess n-type channel conduction, SnO2 based TFTs exhibited anomalous p-type conductivity. Integration of these n- and p-type devices resulted in complementary inverter with a gain of 11.

Enhancement of Photocurrent of Polymer-Gelled Dye-Sensitized Solar Cell by Incorporation of Exfoliated Montmorillonite Nanoplatelets

Abstract: Poly(n-isopropylacrylamide) (PNIPAAm) and its nanocomposite with exfoliated montmorillonite (MMT) were prepared by soap-free emulsion polymerization and individually applied to gel the electrolyte systems for the dye-sensitized solar cells (DSSCs). Each exfoliated MMT nanoplatelet had a thickness of ∼ 1 nm, carried ∼ 1.8 cation/nm2, and acted like a two-dimensional electrolyte. The DSSC with the LiI/I2/tertiary butylpyridine electrolyte system gelled by this polymer nanocomposite had higher short-circuit current density (Jsc) compared to that gelled by the neat PNIPAAm. The former has a Jsc of 12.6 mA/cm2, an open circuit voltage (Voc) of 0.73 V, and a fill factor (FF) of 0.59, which harvested 5.4% electricity conversion efficiency (η) under AM 1.5 irradiation at 100 mW/cm2, whereas the latter has Jsc = 7.28 mA/cm2, Voc = 0.72 V, FF = 0.60, and η = 3.17%. IPCE of the nanocomposite-gelled DSSC were also improved. Electrochemical impedance spectroscopy of the DSSCs revealed that the nanocomposite-gelled electrolytes significantly decreased the impedances in three major electric current paths of DSSCs, that is, the resistance of electrolytes and electric contacts, impedance across the electrolytes/dye-coated TiO2 interface, and Nernstian diffusion within the electrolytes. The results were also consistent with the increased molar conductivity of nanocomposite-gelled electrolytes. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 47–53, 2008

Anomalous p -channel amorphous oxide transistors based on tin oxide and their complementary circuits

Abstract: In this article, we report the fabrication of SnO2 thin film transistors (TFTs) fabricated by reactive evaporation. Different from the previous reports, the fabricated TFTs exhibit p-type conductivity in its undoped form. The postdeposition annealing temperature was tuned to achieve p-channel SnO2 TFTs. The on/off ratio and the field-effect mobility were ∼103 and 0.011cm2∕Vs, respectively. To demonstrate inverter circuit, two devices with different threshold voltages were combined and an output gain of 2.8 was achieved. The realization of p-channel oxide TFTs would open up new challenges in the area of transparent electronics.

Macromolecular Nanotechnology Performance of gelled-type dye-sensitized solar cells associated with glass transition temperature of the gelatinizing polymers

Abstract: Poly(methyl acrylate) (PMA), poly(vinyl acetate) (PVAc) and poly(n-isopropylacrylamide) (PNIPAAm) with their respective Tg of 6, 32, and 145 C were employed to gel the LiI/I2/tertiary butylpyridine electrolyte system for preparation of the gelled-type dye-sensitized solar cells (DSSC). The light-to-electricity conversion efficiencies of DSSCs gelled by PMA, PVAc, and PNIPAAm were 7.17%, 5.62%, and 3.17%, respectively under simulated AM 1.5 sunlight irradiation, implying that utilizing the polymer of lower Tg to gel the electrolytes leaded to better performance of the DSSCs. Their short-circuit current density and IPCE also showed the similar trend. Electrochemical impedance spectroscopy of the gelled DSSCs revealed that utilizing the polymer of lower Tg resulted in lower impedance associated with the Nernstian diffusion within the electrolytes. The results were consistent with the observation that the molar conductivity of gelled electrolytes was higher as the polymer of lower Tg was applied, which can be justified by Vogel–Tammann–Fulcher (VTF) equation.

Controlled Growth of Nanofiber Network Hole Collection Layers with Pore Structure for Polymer−Fullerene Solar Cells

Abstract: In this study, we compare a series of hole collector layers (HCLs) with pore structure fabricated via an electrochemical method to construct polymer−fullerene solar cells. The HCLs with a pore structure can offer a large interface to enhance hole collection; however, the series resistances are also increased by the relatively pore morphology. Photovoltaic device with the largest short circuit current (Jsc) and efficiency is achieved using poly(3,4-propylenedioxythiophene) (PProDoT) as HCLs due to its highly porous structure and reasonable series resistance. By further optimizing the thickness of the HCLs in the solar cell, a power efficiency of 3.57% under simulated sun light is achieved.

Multimode optoelectrochemical detection of cysteine based on an electrochromic Prussian blue electrode

Abstract: In the present work, multiple detection modes of an electrochromic (EC) sensor were studied and compared. We utilized a Prussian blue (PB) thin film modified F-doped tin oxide (FTO) electrode to detect l -cysteine (Cys), a naturally occurring amino acid bearing a thiol group. The sensing was triggered by a cyclic voltammetric (CV) scan and functioned upon the catalytic oxidation of Cys at the surface of a PB/FTO electrode that had been oxidized to the Berlin green (BG) state. With the EC property of PB and the use of transparent FTO electrode, the Cys concentration, denoted as [Cys], could be detected both electrochemically and optically. As a result, the following four types of calibration curves were obtained simultaneously from the same in situ optoelectrochemical measurement: amperometry (current versus [Cys]), coulometry (charge versus [Cys]), potentiometry (potential versus [Cys]), and absorptometry (optical density change versus [Cys]). This proof-of-concept study suggests that the EC detection can provide more informative results than pure electrochemical or optical sensing approach does.

Integrating an Enzyme‐Entrapped Conducting Polymer Electrode and a Prereactor in a Microfluidic System for Sensing Glucose

Abstract: In this study, the flow injection analysis was applied to the enzyme-entrapped electrode on a chip for sensing glucose. The on-chip microelectrode was fabricated by the standard photolithography in clean-room environment and the microfluidic channel height of 100 μm on the chip was formed by poly(dimethylsiloxane). The conducting polymer, poly(3,4-ethylenedioxythiophene), PEDOT, was electropolymerized to entrap the coexisting glucose oxidase (GOD) by cyclic voltammetry (CV). The amount of enzyme entrapped in the matrix measured spectroscopically was about 0.101 U/cm2. At a flow rate of 10 ml/hr, the working electrode (Pt/PEDOT/GOD, WE1) was set at 0.7 V (vs. Ag/AgCl) and sensing of H2O2 was carried out by injecting samples with various concentrations of glucose (Glu). A linear relationship between the sensing current and the glucose concentration, ranging from 1 to 20 mM, was obtained with a sensitivity of 8 nA mm−2 mM−1. The response time and the recovery time were about 30 and 230 s, respectively. For a single-potential test, the oxidation currents of 0.08 mM ascorbic acid (AA) and a blend of 0.08 mM AA and 10 mM Glu reached 31.3% and 145.5%, respectively, when compared with the oxidation current of 10 mM Glu alone. However, when a pre-reactor (WE2) was set at the same potential (0.7 V) before the main enzyme integrated electrode (WE1), the oxidation current for the above mixed solution reached 99.6% of the original one.

Method for improving surface plasmon resonance by using conducting metal oxide as adhesive layer

Abstract: Surface plasmon resonance (SPR) sensing technique which provides high specificity and accuracy has been an important method for molecular sensing technology. In the past, in order to affix 45 nm gold film onto glass or silicon substrate, several nanometers of chromium (Cr) or titanium (Ti) has been used as adhesive layer for the attachment of Au film. However, the existence of Cr or Ti thin film deteriorates the performance of SPR sensor due to their characteristic optical absorption. Our experimental results have confirmed the uses of conducting metal oxide, specifically, ITO and Zinc Oxide (ZnO) can be used to replace Cr or Ti for better performance in terms of SPR resonant properties (resonant angle and HMBW) and sensitivity enhancement for 3 to 15 times than traditional ones. It would contribute significantly to the SPR applications in both biosensors and gas sensors.

A study of partially irreversible characteristics in a TTF–TCNQ gas sensing system

Abstract: The irreversible gas sensing behavior is investigated for TTF–TCNQ complex in the presence of NO 2 or O 2 . Reactions with the gas molecules are the main reason to cause the irreversibility, which has been reported and supported by analytical data. The totally irreversible behavior was noticed when a TTF–TCNQ thin film was brought in contact with NO 2 gas. As for O 2 gas, however, only partially irreversible phenomenon was observed. For a TTF–TCNQ thin film that interacts with NO 2 or O 2 gas, the degree of irreversibility is determined by the competition ratio of the desorption rate to that of the reaction rate. A theory based on the competition concept was proposed and a general expression for three possible behaviors (totally reversible, totally irreversible, and partially reversible cases) in a gas sensing system was obtained. The O 2 sensing data match the theoretical prediction when the reaction and the adsorption are limited at the surface.

NO gas sensor of PEDOT: PSS nanowires by using direct patterning DPN

Abstract: Nitric oxide (NO) detection is a critical issue for environmental safety and medical diagnosis due reasons with regard to the toxic properties for human body and metabolic index for respiratory disease, respectively. Development of gas sensor with high sensitivity is very important because the concentration of NO gas in the environment and respiratory tract is extremely low, therefore not readily detectable. The material with nanostructure can improve the sensitivity of sensor owning to surface effect and size effect. Herein, we developed a new type of gaseous nanosensor assembled by 34 nanowires of conducting polymer, PEDOT: PSS. The nanowires were fabricated by dip pen nanolithography (DPN) with the length of 55 um and diameter of 300 nm between golden wires. The NO gas measurement is based on chemiresistor based methods. The result of dynamic measurement of NO gas at 100 ppm shows repeatability and stability; the recovery time is 10.4 minutes. Moreover, the lowest concentration of NO gas in static measurement is 10ppm at 80 C, which also shows the ability sensing at low temperature.

PH Buffering Hybrid Material and the Forming Method Thereof

Abstract: The present invention discloses a pH buffering hybrid material and the forming method thereof. The pH buffering hybrid material comprises a substrate, a conductive polymer layer on the substrate, and a ZnO nanorod layer produced by deposition of ZnO particles as nucleuses on the conductive polymer layer, and the ZnO particles growing into the ZnO nanorods via hydrothermal reaction. The pH buffering hybrid material has the pH turning ability and the potential of conductivity.