Showing papers by "Kuo-Chuan Ho published in 2009"

Tunable Novel Cyclopentadithiophene-Based Copolymers Containing Various Numbers of Bithiazole and Thienyl Units for Organic Photovoltaic Cell Applications

Abstract: Six novel conjugated copolymers (P1−P6) containing coplanar cyclopentadithiophene (CPDT) units (incorporated with bithiazole/thienyl-based monomers) were synthesized and developed for the applications of polymer solar cells (PSCs). Copolymers P1−P6 covered broad absorption ranges from UV to near-infrared (400−800 nm) with narrow optical band gaps of 1.70−1.94 eV, which are compatible with the maximum solar photon reflux. Partially reversible p- and n-doping processes of P1−P6 in electrochemical experiments were observed. Compared with those previously reported CPDT-based narrow band gap polymers, the proper molecular design for HOMO/LUMO levels of P1−P6 induced relatively high photovoltaic open-circuit voltages in the PSC devices. Powder X-ray diffraction (XRD) analyses suggested that these copolymers formed highly self-assembled π−π stackings. Under 100 mW/cm2 of AM 1.5 white-light illumination, bulk heterojunction PSC devices containing an active layer of electron donor copolymers P1−P6 blended with ele...

Highly porous PProDOT-Et2 film as counter electrode for plastic dye-sensitized solar cells.

Abstract: A poly(3,3-diethyl-3,4-dihydro-2H-thieno-[3,4-b][1,4]dioxepine) (PProDOT-Et2) counter electrode was incorporated in a plastic dye-sensitized solar cell (DSSC) to substitute for Pt electrode. The surface morphology and I-/I3- redox behaviors based on PProDOT-Et2 and sputtered-Pt electrodes were characterized, and their performances as counter electrodes in the plastic-DSSCs were compared. Cells fabricated with a PProDOT-Et2 counter electrode showed a higher conversion efficiency of 5.20% compared with cell fabricated with sputtered-Pt (5.11%) electrodes under the illumination of 100 mW cm(-2). This enhancement was attributed to the increase in the effective surface area and good catalytic properties of PProDOT-Et2 for I3- reduction.

Electrochemical characterization of the solvent-enhanced conductivity of poly(3,4-ethylenedioxythiophene) and its application in polymer solar cells

Abstract: The influence of solvent on the electrochemical property and conductivity of PEDOT has been investigated by electrochemical and physical characterizations. The PEDOT treated with different solvents reveals a different reversibility of ionic transport and cycling stability, which is associated with the conformational rearrangement from aggregated to linear polymer chains, as evidenced from atomic force microscopy (AFM). The conductivity of the PEDOT thin film can also be enhanced while the degree of linear polymer chains is higher. The application of highly conductive PEDOT thin film as a buffer layer in the polymer photovoltaic devices was realized. A PCE of 4.27% for photovoltaic devices based on P3HT–PCBM under simulated sun light is achieved by using a PEDOT thin film treated with DMSO.

Detection of nitrite using poly(3,4-ethylenedioxythiophene) modified SPCEs

Abstract: The poly(3,4-ethylenedioxythiophene) (PEDOT)- and PEDOT/multi-wall carbon nanotubes- (PEDOT/MWCNTs) modified screen-printed carbon electrodes (SPCEs) were fabricated and their catalytic properties towards nitrite were studied. Due to the electrostatic interaction between the negatively-charged nitrite ions and the positively-charged PEDOT film, the operating potential for nitrite oxidation was shifted about 160 mV to negative side, compared to bare SPCE, as a PEDOT film was deposited on the SPCE. The diffusion coefficient obtained from RDE experiment is 2.05×10−5 cm2 s−1. The electron transfer coefficient (α) was increased from 0.515 to 0.615 as the sensing electrode was changed from PEDOT-modified to PEDOT/MWCNTs-modified electrode. Therefore, PEDOT/MWCNTs composite shows the superior catalytic property towards nitrite and the operating potential was further shifted about 100 mV to the negative side. The sensitivity and limit of detection (LOD) for the PEDOT- and PEDOT/MWCNTs-modified SPCEs are about 100 mA cm−2 M−1, 1.72 μM and 140 mA cm−2 M−1, 0.96 μM, respectively. The possible interferences from several common ions were tested. The developed sensor was also applied to the determination of nitrite concentration in tap water sample.

Efficient and stable plastic dye-sensitized solar cells based on a high light-harvesting ruthenium sensitizer

Abstract: A high light-harvesting ability heteroleptic ruthenium complex dye, SJW-E1, was examined as a sensitizer for the plastic dye-sensitized solar cells (DSSCs) constructed by a low-temperature electrode preparation method using binder-free TiO2 paste and an ITO-PEN substrate. The effects of a TiOxbuffer layer, electrolyte composition and co-adsorbents on the cell performance as well as the cell long-term stability were investigated. The TiOxbuffer layer has not only enhanced the adhesion between TiO2 thin film and the ITO/PEN substrate but also reduced the electron recombination, resulting in the improvement of the fill factor (FF) and therefore the photovoltaic performance of the solar cells. The optimized solar cell based on SJW-E1dye showed an efficiency of 6.31%. Furthermore, the plastic DSSCs based on the SJW-E1 dye shows a better cell stability compared to that based on N719dye after a full sunlight soaking (at ca. 50 °C) for 500 h. These results demonstrated that the flexible DSSCs based on the high light-harvesting, well-functionalized heteroleptic ruthenium dye could achieve both high performance and good stability.

Using a PEDOT:PSS modified electrode for detecting nitric oxide gas

Abstract: PEDOT:PSS thick films, prepared by the drop-coated method, were used in this study for sensing nitric oxide (NO) gas The thickness of PEDOT-PSS film was controlled by dropping different volumes of PEDOT-PSS solution to improve the response of PEDOT-PSS film Due to its porous structure, the thicker the PEDOT-PSS film is, the higher the noticeable surface area Thus, a larger response is found However, since the concentration of NO gas used was low (10 ppm), the effect of the surface area was not noticeable when the thickness of the film was greater than 5 μm In the range of 25–10 ppm NO, the relationship between the response of the PEDOT-PSS film and the NO concentration was linear The limit of detection ( S / N = 3), response time ( t 95 ), and recovery time ( t 95 ) were about 350 ppb, 527 s, and 1780 s, respectively The response of PEDOT-PSS film to 10 ppm NO gas was dramatically affected by the presence of either O 2 or CO The standard deviation, with respect to the sensitivity of the NO gas sensor based on PEDOT:PSS film, was 22% The sensitivity of the sensor remained at about 745% that of a fresh one

Fabrication of multilayer organic solar cells through a stamping technique

Abstract: In this article, we demonstrate a simple and reliable stamping technique for fabricating multi-layer solar cells. A poly(di-methylsilane) (PDMS) stamp is used for transferring the active layers onto the substrate. An intermediate solvent treatment is introduced to temporarily modify the PDMS surface; therefore, the polymer film can be uniformly formed on top of the PDMS surface. This method is involves non-contaminative and non-invasive processes, therefore it can avoid possible degradation or contamination of the polymer film and the PDMS stamp can be reused. Devices realized through this stamping technique both by direct and inverted structures exhibited power conversion efficiencies of 3.2 and 2.83% respectively.

Binary room-temperature ionic liquids based electrolytes solidified with Si02 nanoparticles for dye-sensitized solar cells

Abstract: In this study, binary ionic liquids (bi-IL) of imidazolium salts containing cations with different carbon side chain lengths (C = 2, 4, 6, 8) and anions such as iodide (I ― ), tetrafluoroborate (BF 4 ― ), hexafluorophosphate (PF 6 ― ) and trifluoromethansulfonate (SO 3 CF 3 ― ) were used as electrolytes in dye-sensitized solar cells (DSSCs). On increasing the side chain length of imidazolinium salts, the diffusion coefficients of I 3 ― and the cell conversion efficiencies decreased; however, the electron lifetimes in TiO 2 electrode increased. As for different anions, the cell which contains 1-butyl-3-methyl imidazolium trifluoromethansulfonate (BMISO 3 CF 3 ) electrolyte has better performance than those containing BMIBF 4 and BMIPF 6 . From the impedance measurement, the cell containing BMISO 3 CF 3 electrolyte has a small charge transfer resistance (R ct2 ) at the TiO 2 /dye/electrolyte interface. Moreover, the characteristic frequency peak for TiO 2 in the cell based on BMISO 3 CF 3 is less than that of BMIBF 4 and BMIPF 6 , indicating the cell with bi-IL electrolyte based on BMISO 3 CF 3 has higher electron lifetime in TiO 2 electrode. Finally, the solid-state composite was introduced to form solid-state electrolytes for highly efficient DSSCs with a conversion efficiency of 4.83% under illumination of 100 mW cm ―2 . The long-term stability of DSSCs with a solidified bi-IL electrolyte containing SiO 2 nanoparticles, which is superior to that of a bi-IL electrolyte alone, was also presented.

Solvent-Annealing-Induced Self-Organization of Poly(3-hexylthiophene), a High-Performance Electrochromic Material

Abstract: We have systematically studied the self-organization of poly(3-hexylthiophene) (P3HT), an electrochromic material, upon control of the solvent evaporation rate. We characterized these polymer films using atomic force microscopy and X-ray diffraction measurements. Well-ordered P3HT structures were developed after solvent annealing; these highly crystalline structures exhibited enhanced electrochromic contrast and reduced resistance within the film, leading to larger coloration efficiencies and faster switching times. The optical contrast (Δ%T), coloration efficiency, and switching time of the P3HT films increased from 54.2%, 182.6 cm2 C−1, and 5.3 s, respectively, prior to solvent annealing to 64.8%, 293.5 cm2 C−1, and 3.2 s, respectively, after application of the solvent-annealing conditions.

Effects of nanomorphological changes on the performance of solar cells with blends of poly[9,9'-dioctyl-fluorene-co-bithiophene] and a soluble fullerene.

Abstract: Controlled nanophase segregation within the blended films of a conjugated polymer and a soluble fullerene has enabled us to form a continuous transfer pathway for the carriers, thereby increasing the photocurrent generation for polymer photovoltaic devices. Here, we study the effects of nanomorphological changes on the performance of polymer solar cells using blended films of poly[9,9'-dioctyl-fluorene-co-bithiophene] (F8T2) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Different weight ratios of the F8T2 and PCBM blends in various solvents were studied at different annealing temperatures. The morphology of the films seems to be a strong function of the processing conditions. The power conversion efficiency (PCE) of the photovoltaic devices has improved significantly from 0.34% to 2.14% under air mass 1.5 simulated solar illumination (100 mW cm−2), which could be attributed to the nanomorphological changes in the films.

High efficiency quasi-solid-state dye-sensitized solar cell based on polyvinyidene fluoride-co-hexafluoro propylene containing propylene carbonate and acetonitrile as plasticizers

Abstract: Quasi-solid-state dye-sensitized solar cells (DSSCs) with different weight ratios of polyvinyidene fluoride- co -hexafluoro propylene (PVDF-HFP) containing two different plasticizers such as propylene carbonate (PC) and acetonitrile (AN) were fabricated and the effects of TiO 2 morphology, light intensities as well as different organic iodides on the solar cell performance were studied. Two TiO 2 photoelectrodes were designed by the coating of low (P1) and high molecular weight poly(ethylene glycol) (P2) incorporated into the TiO 2 suspension. The DSSCs fabricated with the P2 TiO 2 electrode show better performance in terms of short-circuit current densities ( J SC ) and conversion efficiencies than the P1 for all the weight percentages of PVDF-HFP containing both plasticizers. Further, the maximum current density ( J SC ) and conversion efficiency of PVDF-HFP containing different organic iodides follow the order: TBAI > TPAI > NH 4 I irrespective of the solvents and light intensity. A good conversion efficiency of 6.74% with J SC of 16.04 mA/cm 2 , an open-circuit voltage ( V OC ) of 0.657 V and a fill factor of 0.64 under illumination of 100 mW/cm 2 was obtained for the DSSC with 10% of PVDF-HFP containing 0.4 M of TBAI and 0.04 M of I 2 in PVDF-HFP/AN system.

Enhanced photovoltaic performance by synergism of light-cultivation and electronic localization for highly efficient dye-sensitized solar cells

Abstract: Two ruthenium sensitizers, [Ru(dcbpy)(opip)(NCS)2] (JF-1, dcbpy = 4,4′-dicarboxylic acid-2,2′-bipyridine, opip = 2-(4-octylphenyl)-1H-imidazo[4,5-f][1,10]phenanthroline) and [Ru(dcbpy)(otip)(NCS)2] (JF-2, otip = 2-(5-octylthiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline), with unusually high power-conversion efficiency in comparison with other ruthenium complexes containing 1,10-phenanthroline-based ligands were designed. The power-conversion efficiency of JF-2 is 20% higher than that of JF-1, due to the modification of the ancillary ligand with a thiophene moiety. The origins of this device performance diversity are illustrated by photophysical properties, electrochemical data and density functional theory (DFT) studies. The greater device performance of JF-2 compared to JF-1 was caused from the broader MLCT distribution, the appropriate localization of the frontier orbitals and the stronger driving force of the charge injection and regeneration.

Fabricating an Amperometric Cholesterol Biosensor by a Covalent Linkage between Poly(3-thiopheneacetic acid) and

Abstract: In this study, use of the covalent enzyme immobilization method was proposed to attach cholesterol oxidase (ChO) on a conducting polymer, poly(3-thiopheneacetic acid), (poly(3-TPAA)). Three red-orange poly(3-TPAA) films, named electrodes A, B and C, were electropolymerized on a platinum electrode by applying a constant current of 1.5 mA, for 5, 20 and 100 s, respectively. Further, 1-ethyl-3-(3-dimethylamiopropyl)carbodiimide hydrochloride (EDC·HCl) and N-hydroxysuccinimide (NHS) were used to activate the free carboxylic groups of the conducting polymer. Afterwards, the amino groups of the cholesterol oxidase were linked on the activated groups to form peptide bonds. The best sensitivity obtained for electrode B is 4.49 mA M -1 cm -2 , with a linear concentration ranging from 0 to 8 mM, which is suitable for the analysis of cholesterol in humans. The response time (t95) is between 70 and 90 s and the limit of detection is 0.42 mM, based on the signal to noise ratio equal to 3. The interference of species such as ascorbic acid and uric acid increased to 5.2 and 10.3% of the original current response, respectively, based on the current response of cholesterol (100%). With respect to the long-term stability, the sensing response retains 88% of the original current after 13 days.

Fabricating an Amperometric Cholesterol Biosensor by a Covalent Linkage between Poly(3-thiopheneacetic acid) and Cholesterol Oxidase

Abstract: In this study, use of the covalent enzyme immobilization method was proposed to attach cholesterol oxidase (ChO) on a conducting polymer, poly(3-thiopheneacetic acid), [poly(3-TPAA)]. Three red-orange poly(3-TPAA) films, named electrodes A, B and C, were electropolymerized on a platinum electrode by applying a constant current of 1.5 mA, for 5, 20 and 100 s, respectively. Further, 1-ethyl-3-(3-dimethylamiopropyl)carbodiimide hydrochloride (EDC · HCl) and N-hydroxysuccinimide (NHS) were used to activate the free carboxylic groups of the conducting polymer. Afterwards, the amino groups of the cholesterol oxidase were linked on the activated groups to form peptide bonds. The best sensitivity obtained for electrode B is 4.49 mA M−1 cm−2, with a linear concentration ranging from 0 to 8 mM, which is suitable for the analysis of cholesterol in humans. The response time (t95) is between 70 and 90 s and the limit of detection is 0.42 mM, based on the signal to noise ratio equal to 3. The interference of species such as ascorbic acid and uric acid increased to 5.2 and 10.3% of the original current response, respectively, based on the current response of cholesterol (100%). With respect to the long-term stability, the sensing response retains 88% of the original current after 13 days.