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Find video protocols related to scientific articles indexed in Pubmed.
Random copolymers: novel diketopyrroloppyrrole random copolymers: high charge-carrier mobility from environmentally benign processing (adv. Mater. 38/2014).
Adv. Mater. Weinheim
PUBLISHED: 10-11-2014
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On page 6612, D. S. Chung, Y.-H. Kim, S.-K. Kwon, and co-workers demonstrate a smart molecular-design strategy of polymer semiconductors to achieve their processability in environmentally benign solvents. Random copolymerization between two different DPP-based repeating units enables the polymer to be soluble in a wide range of green solvents including tetralin, and also leads to excellent charge-transport characteristics with a charge-carrier mobility of >5 cm(2) V(-1) s(-1) .
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Naphtho[2,1-b:3,4-b']dithiophene-based Bulk Heterojunction Solar Cells: How Molecular Structure Influences Nanoscale Morphology and Photovoltaic Properties.
Chemphyschem
PUBLISHED: 08-21-2014
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Organic bulk heterojunction photovoltaic devices based on a series of three naphtho[2,1-b:3,4-b']dithiophene (NDT) derivatives blended with phenyl-C71 -butyric acid methyl ester were studied. These three derivatives, which have NDT units with various thiophene-chain lengths, were employed as the donor polymers. The influence of their molecular structures on the correlation between their solar-cell performances and their degree of crystallization was assessed. The grazing-incidence angle X-ray diffraction and atomic force microscopy results showed that the three derivatives exhibit three distinct nanoscale morphologies. We correlated these morphologies with the device physics by determining the J-V characteristics and the hole and electron mobilities of the devices. On the basis of our results, we propose new rules for the design of future generations of NDT-based polymers for use in bulk heterojunction solar cells.
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Interface engineering of a highly sensitive solution processed organic photodiode.
Phys Chem Chem Phys
PUBLISHED: 07-30-2014
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We report on tuning of the interfacial properties of a highly sensitive organic photodiode by introducing a buffer layer between the anode and the semiconductor layer. The effects of different buffer layers consisting of a self-assembled monolayer (SAM), PEDOT:PSS, and pentacene on the morphology and crystallinity of the upper-deposited bulk heterojunction semiconductor layer are carefully analyzed combined with electrical analysis. The active layer is controlled to be nearly homogeneous and to have low crystallinity by using a SAM or PEDOT:PSS buffer layers, whereas a highly crystalline morphology is realized by using the pentacene buffer layer. When exposed to light pulses, the external quantum efficiency and thus the photocurrent are slightly higher for the PEDOT:PSS-based photodiode; however the dark current is the lowest for the pentacene-based photodiode. We discuss the origin of the high sensitivity (a detectivity of 1.3 × 10(12) Jones and a linear dynamic range of 95 dB) of the pentacene-based photodiode, particularly in terms of the morphology-driven low dark current.
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High performance organic nonvolatile flash memory transistors with high-resolution reduced graphene oxide patterns as a floating gate.
ACS Appl Mater Interfaces
PUBLISHED: 05-28-2014
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High-performance organic nonvolatile memory transistors (ONVMTs) are demonstrated, the construction of which is based on novel integration of a highly conductive polymer as a semiconductor layer, hydroxyl-free polymer as a tunneling dielectric layer, and high-resolution reduced graphene oxide (rGO) patterns as a floating gate. Finely patterned rGO, with a line width of 20-120 ?m, was embedded between SiO2 and the polymer dielectric layer, which functions as a nearly isolated charge-trapping center. The resulting ONVMTs demonstrated ideal memory behavior, and the transfer characteristics promptly responded to writing and erasing the gate bias. In particular, the retention time of written/erased states tended to increase as the rGO line width was reduced, implying that the line width is a critical factor in suppressing charge release from rGO. Using a 20-?m-wide rGO pattern, a nonvolatile large memory window (>20 V) was retained for more than 5 × 10(5) s, which is 50 times longer than non-patterned rGO films.
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High mobility polymer based on a ?-extended benzodithiophene and its application for fast switching transistor and high gain photoconductor.
Sci Rep
PUBLISHED: 05-08-2014
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Here we present synthesis and electronic properties of a new alternating copolymer composed of dithieno[2,3-d;2',3'-d']benzo[1,2-b;4,5-b']dithiophene (DTBDT) and diketopyrrolopyrrole units, poly dithienobenzodithiophene-co-diketopyrrolopyrrolebithiophene (PDPDBD). The resulting polymer showed hysteresis free, fast switching and highly reliable organic thin-film transistor properties comparable to a-Si. Hole mobility of the polymer is about 2.7 cm(2)V(-1)s(-1), which is remarkably improved compared with its benzodithiophene (BDT)-analougue that contains a smaller aromatic ring of BDT in the place of DTBDT. This is mainly due to much increased intramolecular charge transport originated from PDPDBD's rigid molecular backbone. Furthermore, photoconductor devices fabricated by using PDPDBD as an active layer showed a high performance with the highest photoconductive gain of ~10(5). Taken together, the successful PDPDBD's transistor and photoconductor performances with high device stability demonstrated practical applicability of PDPDBD in low-cost and flexible optoelectronic devices.
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Al2O3/TiO2 nanolaminate thin film encapsulation for organic thin film transistors via plasma-enhanced atomic layer deposition.
ACS Appl Mater Interfaces
PUBLISHED: 04-18-2014
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Organic electronic devices require a passivation layer that protects the active layers from moisture and oxygen because most organic materials are very sensitive to such gases. Passivation films for the encapsulation of organic electronic devices need excellent stability and mechanical properties. Although Al2O3 films obtained with plasma enhanced atomic layer deposition (PEALD) have been tested as passivation layers because of their excellent gas barrier properties, amorphous Al2O3 films are significantly corroded by water. In this study, we examined the deformation of PEALD Al2O3 films when immersed in water and attempted to fabricate a corrosion-resistant passivation film by using a PEALD-based Al2O3/TiO2 nanolamination (NL) technique. Our Al2O3/TiO2 NL films were found to exhibit excellent water anticorrosion and low gas permeation and require only low-temperature processing (<100 °C). Organic thin film transistors with excellent air-stability (52 days under high humidity (a relative humidity of 90% and a temperature of 38 °C)) were fabricated.
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The effect of branched versus linear alkyl side chains on the bulk heterojunction photovoltaic performance of small molecules containing both benzodithiophene and thienopyrroledione.
Phys Chem Chem Phys
PUBLISHED: 03-25-2014
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To evaluate the effect of side chain characteristics on the photovoltaic performance of small molecules containing both benzodithiophene (BDT) and thienopyrroledione (TPD), we designed and synthesized two such molecules, one containing a branched 2-ethylhexyl (2EH) side chain on the BDT unit (BDTEH-TTPD) and the other containing a linear n-octyl (C8) side chain on the BDT unit (BDTO-TTP). The optical and electrochemical properties and crystalline structures of these molecules were examined. Compared to BDTO-TTPD, BDTEH-TTPD, showed stronger light absorption, longer-range ordering and shorter ?-? stacking distances between backbones. As a result, the power conversion efficiency of a bulk heterojunction solar cell based on BDTEH-TTPD (2.40%) was substantially higher than that of the BDTO-TTPD device (1.12%).
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Novel diketopyrroloppyrrole random copolymers: high charge-carrier mobility from environmentally benign processing.
Adv. Mater. Weinheim
PUBLISHED: 02-24-2014
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The random copolymerization between two different diketopyrrolopyrole-based conducting units represents a suitable synthetic strategy to increase the solubility of polymer semiconductors in a non-chlorinated solvent, without compromising the high charge-carrier mobility. Highly performing thin-film transistors processed from environmentally benign solvents such as tetralin are demonstrated for the first time, resulting in a mobility of greater than 5 cm(2) V(-1) s(-1) .
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Achieving high sensitivity in hybrid photodetectors based on an organic single crystal and an inorganic nanocrystal array.
Nanotechnology
PUBLISHED: 12-17-2013
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We demonstrate an approach to enhance the photosensitivity of an organic single-crystal photodetector by combining it with a nanocrystal (NC) array. A systematic study of the dependence of the photodetector performance on illumination wavelength and light power together with the charge carrier mobility reveals that charge separation at the single-crystal/CdSe NC interface and subsequent electron trapping in the CdSe NCs generates effective photoconductive gain by hole circulation through the high-mobility single crystal. As a result, the responsivity and specific detectivity reached values up to 50 A W(-1) and 2 × 10(9) cm Hz(1/2) W(-1), respectively.
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Record high hole mobility in polymer semiconductors via side-chain engineering.
J. Am. Chem. Soc.
PUBLISHED: 09-25-2013
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Charge carrier mobility is still the most challenging issue that should be overcome to realize everyday organic electronics in the near future. In this Communication, we show that introducing smart side-chain engineering to polymer semiconductors can facilitate intermolecular electronic communication. Two new polymers, P-29-DPPDBTE and P-29-DPPDTSE, which consist of a highly conductive diketopyrrolopyrrole backbone and an extended branching-position-adjusted side chain, showed unprecedented record high hole mobility of 12 cm(2)/(V·s). From photophysical and structural studies, we found that moving the branching position of the side chain away from the backbone of these polymers resulted in increased intermolecular interactions with extremely short ?-? stacking distances, without compromising solubility of the polymers. As a result, high hole mobility could be achieved even in devices fabricated using the polymers at room temperature.
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Charge transport characteristics of a high-mobility diketopyrrolopyrrole-based polymer.
Phys Chem Chem Phys
PUBLISHED: 08-03-2013
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In this study, we attempt to unveil the charge-transport abnormality of the widely studied diketopyrrolopyrrole (DPP)-based polymers with exceptionally high charge carrier mobility [>5 cm(2) V(-1) s(-1)]. Based on the electric field and temperature dependence of the charge-transport characteristics of the field effect transistor (FET) geometry of one of the highly conductive DPP derivatives, namely, (poly[2,5-bis(7-decylnonadecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-(E)-(1,2-bis(5-(thiophen-2-yl)selenophen-2-yl)ethene) (PDPPDTSE), we show that the high gate-source bias drew the carriers closer to the interface of the semiconductor/dielectric layers where the density of state (DOS) of the charge carrier is significantly broader than the bulk. We argue that the intrinsically narrow DOS in the PDPPDTSE bulk resulted in significantly different charge-transport behavior between the semiconductor bulk and the semiconductor/dielectric interface, which was not visible in the other low-mobility organic semiconductors that contain intrinsically high density of trap states in their bulk. To avoid these charge transport abnormalities, we try to operate the FETs under low gate bias without compromising the accumulated charge carrier density. By carefully employing a thin metal oxide covered with a self-assembled monolayer (SAM) as a dielectric layer, we can demonstrate low-voltage PDPPDTSE FETs with near-ideal performance both in terms of hysteresis-free operation and operating reliability while maintaining a high charge carrier mobility of ~2.8 cm(2) V(-1) s(-1).
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Effect of solvent on detectivity of solution-processed polymer photodetectors.
Opt Lett
PUBLISHED: 08-02-2013
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We demonstrate a high-performance solution-processed polymer photodetector (PPD) whose detectivity (D*) exceeds 10(11) Jones over almost the entire range of visible light. PPDs processed from a chlorobenzene solution using 1,8-diiodooctane (DIO) as an additive exhibit large crystalline domains with long-range order, in contrast to the featureless morphology of PPDs processed with pure solvent. Moreover, PPDs processed with DIO exhibit higher charge carrier mobility, and thus high photoconductive gain without compromising long carrier lifetime. Consequently, a high-loading ratio of DIO (3%) yielded a PPD whose D* in the visible range was over threefold higher than that of PPD without DIO.
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Synthesis and transistor properties of asymmetric oligothiophenes: relationship between molecular structure and device performance.
Chemistry
PUBLISHED: 07-04-2013
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A series of three thiophene-naphthalene-based asymmetric oligomers-5-decyl-2,2:5,2:5,2-quaterthiophene (DtT), 5-decyl-5-(naphthalen-2-yl)-2,2:5,2-terthiophene (D3TN), and 5-(4-decylphenyl)-5-(naphthalen-2-yl)-2,2-bithiophene (DP2TN)-was synthesized by Suzuki cross-coupling reactions. The long alkyl side chains improved both the solubility of the oligomers in solvents and their tendency to self-assemble. UV/Vis absorption measurements suggested that DtT, D3TN, and DP2TN form H-type aggregates with a face-to-face packing structure. In addition, the three oligomers were found to adopt vertically aligned crystalline structures in films deposited on substrates, as revealed by grazing-incidence wide-angle X-ray scattering. These oligomers were used as the active layers of p-type organic field-effect transistors, and the resulting devices showed field-effect mobilities of 3.3×10(-3) ?cm(2) ?V(-1) ?s(-1) for DtT, 1.6×10(-2) ?cm(2) ?V(-1) ?s(-1) for D3TN, and 3.7×10(-2) ?cm(2) ?V(-1) ?s(-1) for DP2TN. The differences in transistor performances were attributed to the degree of ? overlap and the morphological differences determined by the molecular structures.
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Synthesis of a low-bandgap fluorinated donor-acceptor copolymer and its optoelectronic application.
ACS Appl Mater Interfaces
PUBLISHED: 06-26-2013
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We demonstrate the synthesis of a new copolymer which is composed of dialkyl thienylated benzodithiophene and perfluororalkyl-carbonyl thienothiophene (DTBDT-TTFO) and the characterization of its optoelectronic properties. The introduction of thienyl groups enabled the extended delocalization of ? electrons in the DTBDT-TTFO backbone and efficient intermolecular charge transport as proved by the fairly high field effect mobility of 0.02 cm(2)/(V s). The introduction of perfluororalkyl-carbonyl side chains resulted in a significant red-shift of DTBDT-TTFO in the absorption spectra and a decrease in the HOMO and LUMO levels. The resulting energy levels of DTBDT-TTFO were not satisfactory for solar cell applications, especially in terms of charge separation at the polymer/PCBM interfaces. Rather, the DTBDT-TTFO showed better energy level matching with the colloidal nanocrystals (NCs) of CdSe. A photodetector based on the bulkheterojunction of DTBDT-TTFO and CdSe NCs with coplanar device geometry resulted in a high photoconductive gain (responsivity higher than 1A/W under a low operating voltage of 1 V), possibly arising from electron trapping at CdSe NCs such that the hole can travel along the detector and its surrounding circuit. More importantly, the photodetector revealed a time constant of a few hundreds of microseconds, which means that the response speed of the photodetector is fast enough for lag-free imaging applications.
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Enhanced performance of organic light emitting device by incorporating 4,4-bis(2,2-diphenylvinyl)-1,1-biphenyl as an efficient hole-injection nano-layer.
J Nanosci Nanotechnol
PUBLISHED: 06-13-2013
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Here we reported that 4,4-bis(2,2-diphenylvinyl)-1,1-biphenyl (DPVBi), known as blue emitting host material, could effectively manipulate the Schottky energy barrier between the indium tin oxide (ITO) and the emitting layer and thus significantly enhanced hole injection property. As a result, we could greatly improve the current and luminance efficiencies of organic light emitting diodes (OLEDs) as well as their stability. We attributed the enhanced performance of hole injection layer (HIL)-modified OLEDs to the lowered hole injection barrier. By analyzing the J-V characteristics of hole only devices as a function of temperature, we could show that the interfacial energy barrier between ITO and emitting layer was reduced by more than 0.2 eV by insertion of DPVBi HIL.
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Plum coatings of lemongrass oil-incorporating carnauba wax-based nanoemulsion.
J. Food Sci.
PUBLISHED: 06-05-2013
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Nanoemulsions containing lemongrass oil (LO) were developed for coating plums and the effects of the nanoemulsion coatings on the microbial safety and physicochemical storage qualities of plums during storage at 4 and 25 °C were investigated. The emulsions used for coating were produced by mixing a carnauba wax-based solution (18%, w/w) with LO at various concentrations (0.5% to 4.0%, w/w) using dynamic high pressure processing at 172 MPa. The coatings were evaluated for their ability to inhibit the growth of Salmonella Typhimurium and Escherichia coli O157:H7 and their ability to preserve various physicochemical qualities of plums. Uniform and continuous coatings on plums, formed with stable emulsions, initially inhibited S. Typhimurium and E. coli O157:H7 by 0.2 to 2.8 and 0.8 to 2.7 log CFU/g, respectively, depending on the concentration of LO and the sequence of coating. The coatings did not significantly alter the flavor, fracturability, or glossiness of the plums. The antimicrobial effects of the coatings against S. Typhimurium and E. coli O157:H7 were demonstrated during storage at 4 and 25 °C. The coatings reduced weight loss and ethylene production by approximately 2 to 3 and 1.4 to 4.0 fold, respectively, and also retarded the changes in lightness and the concentration of phenolic compounds in plums during storage. The firmness of coated plums was generally higher than uncoated plums when stored at 4 °C and plum respiration rates were reduced during storage. Coatings containing nanoemulsions of LO have the potential to inhibit Salmonella and E. coli O157:H7 contamination of plums and may extend plum shelf life.
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Solvent Additive to Achieve Highly Ordered Nanostructural Semicrystalline DPP Copolymers: Toward a High Charge Carrier Mobility.
Adv. Mater. Weinheim
PUBLISHED: 03-29-2013
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A facile spin-coating method in which a small percentage of the solvent additive, 1-chloronaphthalene (CN), is found to increase the drying time during film deposition, is reported. The field-effect mobility of a PDPPDBTE film cast from a chloroform-CN mixed solution is 0.46 cm(2) V(-1) s(-1) . The addition of CN to the chloroform solution facilitates the formation of highly crystalline polymer structures.
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Synthesis of poly(benzothiadiazole-co-dithienobenzodithiophenes) and effect of thiophene insertion for high-performance polymer solar cells.
Chemistry
PUBLISHED: 02-04-2013
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We describe herein the synthesis of novel donor-acceptor conjugated polymers with dithienobenzodithiophenes (DTBDT) as the electron donor and 2,1,3-benzothiadiazole as the electron acceptor for high-performance organic photovoltaics (OPVs). We studied the effects of strategically inserting thiophene into the DTBDT as a substituent on the skeletal structure on the opto-electronic performances of fabricated devices. From UV/Vis absorption, electrochemical, and field-effect transistor analyses, we found that the thiophene-containing DTBDT derivative can substantially increase the orbital overlap area between adjacent conjugated chains and thus dramatically enhance charge-carrier mobility up to 0.55?cm(2) ?V(-1) ?s(-1). The outstanding charge-transport characteristics of this polymer allowed the realization of high-performance organic solar cells with a power conversion efficiency (PCE) of 5.1?%. Detailed studies on the morphological factors that enable the maximum PCE of the polymer solar cells are discussed along with a hole/electron mobility analysis based on the space-charge-limited current model.
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Band-like transport, high electron mobility and high photoconductivity in all-inorganic nanocrystal arrays.
Nat Nanotechnol
PUBLISHED: 03-08-2011
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Flexible, thin-film electronic and optoelectronic devices typically involve a trade-off between performance and fabrication cost. For example, solution-based deposition allows semiconductors to be patterned onto large-area substrates to make solar cells and displays, but the electron mobility in solution-deposited semiconductor layers is much lower than in semiconductors grown at high temperatures from the gas phase. Here, we report band-like electron transport in arrays of colloidal cadmium selenide nanocrystals capped with the molecular metal chalcogenide complex In(2)Se(4)(2-), and measure electron mobilities as high as 16 cm(2) V(-1) s(-1), which is about an order of magnitude higher than in the best solution-processed organic and nanocrystal devices so far. We also use CdSe/CdS core-shell nanoparticles with In(2)Se(4)(2-) ligands to build photodetectors with normalized detectivity D* > 1 × 10(13) Jones (I Jones = 1 cm Hz(1/2) W(-1)), which is a record for II-VI nanocrystals. Our approach does not require high processing temperatures, and can be extended to different nanocrystals and inorganic surface ligands.
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A new amorphous semiconducting polythiophene for high-performance organic thin-film transistors.
ACS Appl Mater Interfaces
PUBLISHED: 04-15-2010
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A new amorphous semiconducting polymer containing dodecylthiophene rings and a rigid thieno[3,2-b]thiophene ring, poly(2,5-bis(3-dodecyl-2,2-bithiophen-5-yl)thieno[3,2-b]thiophene) (NAP), was synthesized via a microwave-assisted Stille coupling reaction. The presence of the flexible unsubstituted thiophene ring units next to the rigid fused thiophene ring caused NAP to have an amorphous structure. This structure was confirmed by XRD, AFM, and computational calculations. In particular, the out-of-plane XRD patterns of NAP thin films exhibited no reflection peaks before or after the annealing process, indicating that the films had amorphous microstructures. In addition, AFM images of the NAP thin films showed amorphous surface morphologies with very small root-mean-square (rms) surface roughnesses of 0.3-0.5 nm, independent of surface treatment or heat treatment. Computational calculations performed to investigate the preferred conformation of the polymer confirmed the amorphous characteristics of the NAP structure. On the basis of these findings, we propose how an amorphous NAP semiconductor can maintain high carrier mobility. A NAP-based TFT device exhibited a very high carrier mobility of 0.02 cm(2) V(-1) s(-1) with an on/off ratio of 1 x 10(5) and a very small threshold voltage of -2.0 V. This carrier mobility is the highest yet reported for TFTs based on amorphous semiconductors. Thus, the present findings suggest that an amorphous semiconductor layer comprised of NAP would be suitable for use in high-performance organic TFTs fabricated via simple processes in which neither surface treatment nor heat treatment is necessary.
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Solution-processed organic photovoltaic cells with anthracene derivatives.
ChemSusChem
PUBLISHED: 03-31-2010
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Solution-processed small-molecule bulk heterojunction photovoltaic cells are fabricated by using [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) as electron acceptor and triisopropylsilylethynyl anthracene (TIPSAnt) derivatives substituted with naphthalene (TIPSAntNa) and bithiophene (TIPSAntBT) as electron donors. In contrast to TIPS-pentacene, the TIPSAnt derivatives are not susceptible to Diels-Alder reactions with PCBM when processed in solution, as confirmed by UV/Vis measurements. Photoluminescence quenching measurements show exciton diffusion lengths of 5 and 3 nm for TIPSAntBT and TIPSAntNa, respectively. Blending TIPSAntBT and TIPSAntNa with PCBM (1:1, 1:2, 1:3, and 1:4 weight ratios) produces films that possess adequate hole and electron mobilities. The morphological changes that result from varying the blending ratio range from obvious phase-segregated crystalline domains at a 1:1 ratio to homogeneous, nearly amorphous phases at a 1:4 ratio. Bulk heterojunction solar cells prepared by using a TIPSAntBT:PCBM blend reach power conversion efficiencies as high as 1.4 %.
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New anthracene-thiophene-based copolymers that absorb across the entire UV-vis spectrum for application in organic solar cells.
Chem. Commun. (Camb.)
PUBLISHED: 01-13-2010
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We report a new class of anthracene-thiophene-based copolymers, PAT4. The UV-vis absorption spectrum of PAT4 was broad and covered the full range of the solar spectrum. The hole mobility of PAT4 was high, up to 0.037 cm(2) V(-1) s(-1). PAT4-based organic solar cells showed promising power conversion efficiencies of 1.7%.
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Solution-processed flexible ZnO transparent thin-film transistors with a polymer gate dielectric fabricated by microwave heating.
Nanotechnology
PUBLISHED: 10-22-2009
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We report the development of solution-processed zinc oxide (ZnO) transparent thin-film transistors (TFTs) with a poly(2-hydroxyethyl methacrylate) (PHEMA) gate dielectric on a plastic substrate. The ZnO nanorod film active layer, prepared by microwave heating, showed a highly uniform and densely packed array of large crystal size (58 nm) in the [002] direction of ZnO nanorods on the plasma-treated PHEMA. The flexible ZnO TFTs with the plasma-treated PHEMA gate dielectric exhibited an electron mobility of 1.1 cm(2) V(-1) s(-1), which was higher by a factor of approximately 8.5 than that of ZnO TFTs based on the bare PHEMA gate dielectric.
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High-mobility anthracene-based X-shaped conjugated molecules for thin film transistors.
Chem. Commun. (Camb.)
PUBLISHED: 07-28-2009
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New anthracene-based X-shaped conjugated molecules and for use as highly soluble p-type organic semiconductors were developed and exhibited large field-effect mobilities of 0.04 cm(2) V(-1) s(-1) (I(on)/I(off) = 2.8 x 10(5)) and 0.24 cm(2) V(-1) s(-1) (I(on)/I(off) = 5.4 x 10(6)) for devices of and , respectively.
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Effect of selenophene in a DPP copolymer incorporating a vinyl group for high-performance organic field-effect transistors.
Adv. Mater. Weinheim
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A new polymeric semiconductor, PDPPDTSE, is reported which is composed of a diketopyrrolopyrrole moiety and selenophenylene vinylene selenophene, with a high field-effect mobility achieved through intermolecular donor-acceptor interactions. The field-effect mobility of OFET devices based on PDPPDTSE by spin-casting is 4.97 cm(2) V(-1) s(-1) , which is higher than predecessor polymeric semiconductors.
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Morphology-driven high-performance polymeric photodetector.
ACS Appl Mater Interfaces
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The influence of polymer/fullerene morphology on photodetector performance is reported. Various morphologies of spin-coated films are generated by different blending ratio. Morphological study combined with measurement of charge carrier mobility reveals that blend films with an excess content of crystalline fullerene have a phase-separated morphology, resulting in enhanced charge carrier mobility. Under this phase separated morphology, photovoltaic performance is enhanced because of the generation of percolating pathways for charge carriers. Interestingly, however, a homogeneous morphology is found to be more beneficial for photodetector application than this phase separated morphology. An optimized device displayed 3 dB bandwidth up to 1 kHz and detectivities up to D = 1.1 × 10(10) cm Hz(1/2) W(-1). These results emphasize the importance of developing an independent strategy for designing high performance photodetectors separately from solar cell devices both in terms of materials and device geometry. Possible relations between morphology and various figures of merit of photodetectors are discussed.
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Symmetric long alkyl chain end-capped anthracene derivatives for solution-processed organic thin-film transistors.
J Nanosci Nanotechnol
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Three new anthracene derivatives, 2,6-bis(4-decylphenyl)anthracene (DDPAnt), 2-decyl-5-(2-(5-decylthiophen-2-yl)anthracen-6-yl)thiophene (DDTAnt), and 2,6-bis(4-decyloxy phenyl) anthracene (DDPXAnt) were synthesized by Suzuki cross-coupling reaction. The obtained oligomers were characterized by 1H NMR, FT-IR, Mass, UV-visible spectroscopy, cyclovotammetry, differencial scanning calorimetry, and thermogravimetric analysis. The thermal studies show that these oligomers are stable up to 400 degrees C. The solution processed OTFTs were fabricated using synthesized oligomers by spin-coating and drop casting processes on Si/SiO2. OTFTs based on DDPAnt showed the mobility of 7.6 x 10(-3) cm2/Vs and on/off ratio of 10(5).
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Effect of metal ions on photoluminescence, charge transport, magnetic and catalytic properties of all-inorganic colloidal nanocrystals and nanocrystal solids.
J. Am. Chem. Soc.
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Colloidal semiconductor nanocrystals (NCs) provide convenient "building blocks" for solution-processed solar cells, light-emitting devices, photocatalytic systems, etc. The use of inorganic ligands for colloidal NCs dramatically improved inter-NC charge transport, enabling fast progress in NC-based devices. Typical inorganic ligands (e.g., Sn(2)S(6)(4-), S(2-)) are represented by negatively charged ions that bind covalently to electrophilic metal surface sites. The binding of inorganic charged species to the NC surface provides electrostatic stabilization of NC colloids in polar solvents without introducing insulating barriers between NCs. In this work we show that cationic species needed for electrostatic balance of NC surface charges can also be employed for engineering almost every property of all-inorganic NCs and NC solids, including photoluminescence efficiency, electron mobility, doping, magnetic susceptibility, and electrocatalytic performance. We used a suite of experimental techniques to elucidate the impact of various metal ions on the characteristics of all-inorganic NCs and developed strategies for engineering and optimizing NC-based materials.
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Low voltage, hysteresis free, and high mobility transistors from all-inorganic colloidal nanocrystals.
Nano Lett.
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High-mobility solution-processed all-inorganic solid state nanocrystal (NC) transistors with low operation voltage and near-zero hysteresis are demonstrated using high-capacitance ZrO(x) and hydroxyl-free Cytop gate dielectric materials. The use of inorganic capping ligands (In(2)Se(4)(2-) and S(2-)) allowed us to achieve high electron mobility in the arrays of solution-processed CdSe nanocrystals. We also studied the hysteresis behavior and switching speed of NC-based field effect devices. Collectively, these analyses helped to understand the charge transport and trapping mechanisms in all-inorganic NCs arrays. Finally, we have examined the rapid thermal annealing as an approach toward high-performance solution-processed NCs-based devices and demonstrated transistor operation with mobility above 30 cm(2)/(V s) without compromising low operation voltage and hysteresis.
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Comparison of visceral fat and liver fat as risk factors of metabolic syndrome.
J. Korean Med. Sci.
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The principal objective of this study was to determine whether visceral fat or liver fat is a more relevant risk factor for metabolic syndrome. A total of 98 subjects aged 18-65 yr, who visited a health promotion center in a university hospital, were enrolled in this study. Metabolic syndrome was diagnosed based on the modified National Cholesterol Education Programs Adult Treatment Panel III report (NCEP-ATPIII) criteria. We defined the visceral obesity as a visceral fat area of ? 100 cm(2) which was acquired by CT at the L4-5 level. To evaluate fatty liver, we applied a liver-to-spleen attenuation ratio ? 1.1 as measured by CT at the T12 level. We employed binary logistic regression models that used the presence or absence of metabolic syndrome as a dependent variable and age, sex, and the presence or absence of visceral obesity and fatty liver as independent variables. Visceral obesity was not found to be an independent variable as a risk factor of metabolic syndrome (odds ratio 2.7; 95% confidence interval 0.55-13.30), but fatty liver was found to be significant in this model (odds ratio 71.3; 95% CI 13.04-389.53). Our study suggests that liver fat may be a more important risk factor than visceral fat in terms of its association with metabolic syndrome.
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