Showing papers by "Wen-Chang Chen published in 2015"

Conjugated Polymer Nanoparticles as Nano Floating Gate Electrets for High Performance Nonvolatile Organic Transistor Memory Devices

Abstract: A molecular nano-floating gate (NFG) of pentacene-based transistor memory devices is developed using conjugated polymer nanoparticles (CPN) as the discrete trapping sites embedded in an insulating polymer, poly (methacrylic acid) (PMAA). The nanoparticles of polyfluorene (PF) and poly(fluorene-alt-benzo[2,1,3]thiadiazole (PFBT) with average diameters of around 50–70 nm are used as charge-trapping sites, while hydrophilic PMAA serves as a matrix and a tunneling layer. By inserting PF nanoparticles as the floating gate, the transistor memory device reveals a controllable threshold voltage shift, indicating effectively electron-trapping by the PF CPN. The electron-storage capability can be further improved using the PFBT-based NFG since their lower unoccupied molecular orbital level is beneficial for stabilization of the trapped charges, leading a large memory window (35 V), retention time longer than 104 s with a high ON/OFF ratio of >104. In addition, the memory device performance using conjugated polymer nanoparticle NFG is much higher than that of the corresponding polymer blend thin films of PF/polystyrene. It suggests that the discrete polymer nanoparticles can be effectively covered by the tunneling layer, PMAA, to achieve the superior memory characteristics.

Single‐Crystal C60 Needle/CuPc Nanoparticle Double Floating‐Gate for Low‐Voltage Organic Transistors Based Non‐Volatile Memory Devices

Abstract: Low-voltage organic field-effect transistor memory devices exhibiting a wide memory window, low power consumption, acceptable retention, endurance properties, and tunable memory performance are fabricated The performance is achieved by employing single-crystal C60 needles and copper phthalocyanine nanoparticles to produce an ambipolar (hole/electron) trapping effect in a double floating-gate architecture

Effect of Spacer Length of Siloxane‐Terminated Side Chains on Charge Transport in Isoindigo‐Based Polymer Semiconductor Thin Films

Abstract: A series of isoindigo-based conjugated polymers (PII2F-CmSi, m = 3–11) with alkyl siloxane-terminated side chains are prepared, in which the branching point is systematically “moved away” from the conjugated backbone by one carbon atom. To investigate the structure–property relationship, the polymer thin film is subsequently tested in top-contact field-effect transistors, and further characterized by both grazing incidence X-ray diffraction and atomic force microscopy. Hole mobilities over 1 cm2 V−1 s−1 is exhibited for all soluble PII2F-CmSi (m = 5–11) polymers, which is 10 times higher than the reference polymer with same polymer backbone. PII2F-C9Si shows the highest mobility of 4.8 cm2 V−1 s−1, even though PII2F-C11Si exhibits the smallest π–π stacking distance at 3.379 A. In specific, when the branching point is at, or beyond, the third carbon atoms, the contribution to charge transport arising from π–π stacking distance shortening becomes less significant. Other factors, such as thin-film microstructure, crystallinity, domain size, become more important in affecting the resulting device's charge transport.

A silole copolymer containing a ladder-type heptacylic arene and naphthobisoxadiazole moieties for highly efficient polymer solar cells

Abstract: We report a combination of a silole containing ladder-type heptacylic arene and naphthobisoxadiazole moieties for highly efficient polymer solar cells. This new class of PSiNO polymer possesses a planar, rigid backbone and a low-ordering framework. This unique feature facilitates chain extension, leading to high hole mobility and hence a high PCE of 8.37% without further thermal annealing.

Oligosaccharide Carbohydrate Dielectrics toward High‐Performance Non‐volatile Transistor Memory Devices

Abstract: Oligosaccharides are one of the most promising biomaterials because they are abundant, renewable, diversified, and biosourced. The use of oligo- or polysaccharides for high-performance non-volatile organic field-effect-transistor memory is demonstrated herein. The charge-storage mechanism is attributed to charged hydroxyl groups that induce stronger hydrogen bonding, thus leading to the stabilization of trapped charges. This study reveals a promising future for green memory devices.

Interplay of Molecular Orientation, Film Formation, and Optoelectronic Properties on Isoindigo- and Thienoisoindigo-Based Copolymers for Organic Field Effect Transistor and Organic Photovoltaic Applications

Abstract: A systematic study on the effects of heteroarenes on the solid state structure and optoelectronic properties of isoindigo analogues, namely, PBDT-IIG and PBDT-TIIG, used in solution-processed organic field effect transistors (OFETs) and organic photovoltaics (OPVs) is reported. We discover that the optical absorption, frontier orbitals, backbone coplanarity, molecular orientation, solubility, film morphology, charge carrier mobility, and solar cell performance are critically influenced by the heteroarenes in the acceptor subunits. PBDT-IIG exhibits good p-type OFET performance with mobility up to 1.03 × 10–1 cm2 V–1 s–1, whereas PBDT-TIIG displays ambipolar mobilities of μh = 7.06 × 10–2 cm2 V–1 s–1 and μe = 2.81 × 10–4 cm2 V–1 s–1. PBDT-IIG and PBDT-TIIG blended with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) yield promising power conversion efficiencies (PCEs) of 5.86% and 2.55%, respectively. The excellent mobility of PBDT-IIG can be attributable to the growing fraction of edge-on packing by t...

Electrospun Poly(3‐hexylthiophene) Nanofibers with Highly Extended and Oriented Chains Through Secondary Electric Field for High‐Performance Field‐Effect Transistors

Abstract: An extra electric fi eld is introduced below the spinneret in an electrospinning setup for producing poly(3-hexylthiophene) (P3HT) nanofi bers. The liquid jet is greatly prolonged by the additional extensional force and thinner fi bers can thus be obtained. The chain conformation and orientation in fiare probed by differential scanning calorimetry and X-ray diffraction techniques. Under the infl uence of the secondary electric fi eld, P3HT chains are extensively stretched and aligned along the fi ber axis. The electrospun P3HT nanofi bers are fabricated into fi eld-effect transistors and the charge carrier mobilities of the nanofi bers with and without secondary electric fi eld are found to be 1.54 × 10 −4 and 1.62 × 10 −1 cm 2 V −1 s −1 , respectively. The dramatic enhancement of mobility by more than 1000 times is due to the effective charge transport through the delocalization of electrons along the highly extended and oriented P3HT backbones rather than the ordinary π‐π stacking. In addition to P3HT, it is found that this simple method also works for poly(3-alkylthiophene).

Electrospun nanofibers with dual plasmonic-enhanced luminescent solar concentrator effects for high-performance organic photovoltaic cells

Abstract: We fabricated dual functional electrospun (ES) nanofibers by a coaxial electrospinning technique for enhancing the organic photovoltaic (OPV) device efficiency. The nanofibers contained poly[2,7-(9,9-dihexylfluorene)-alt-4,7-(2,1,3-benzothiadiazole)] (PFBT) nanoparticles as the luminescent solar concentrator (LSC) and Ag nanoparticles for the surface plasmon resonance (SPR) effect. Aligned- and crossed-fiber architecture patterns were fabricated to compare the effects of the architecture on the OPV efficiency. The plasmonic-enhanced LSC ES nanofibers with crosslinked poly(methacrylic acid) could be directly integrated into the conventional OPV configuration without sacrificing the coverage area of the active layer. In addition, the in situ reduction of Ag nanoparticles simultaneously enhanced the exciton generation of PFBT and the active materials with the SPR effect. The dual functional ES nanofibers with a crossed-pattern embedded into OPV devices provided significant light harvesting through down conversion and enhanced exciton generation. They led to PCE values of 4.11 and 7.12% for P3HT (poly(3-hexylthiophene)) : PC61BM ([6,6]-phenyl C61-butyric acid methyl ester) and PTB7 (polythieno[3,4-b]-thiophene-co-benzodithiophene) : PC71BM ([6,6]-phenyl C71-butyric acid methyl ester) ([6,6]-phenyl) photovoltaic cells, respectively, which are 18% enhancements compared to their parent devices. This interface-modification approach using plasmonic-enhanced LSC ES nanofibers provides a new approach for enhancing the OPV device performance.

Poly(3-hexylthiophene)–graphene composite-based aligned nanofibers for high-performance field effect transistors

Abstract: We report the morphology and field effect transistor (FET) characteristics of aligned electrospun nanofibers prepared from poly(3-hexylthiophene) (P3HT)–graphene composites. The graphene flakes were more uniformly distributed in the nanofibers compared with spin-coated films, leading to different FET characteristics. The geometrical confinement from electrospun nanofibers resulted in enhanced π–π molecular packing with highly ordered orientation and reduced the grain boundaries under strong stretching forces, thereby increasing carrier mobility. The graphene behaved as an electrically conducting bridge between the P3HT domains in the composites, and thus the FET mobility generally increased as the graphene composition increased. Remarkably, the ES-PG4 FET had the highest hole mobility of 1.82 cm2 V−1 s−1 and a moderately high ION/IOFF of 5.88 × 104, which also exhibited good environmental stability for its transfer characteristics. The experimental results indicated that semiconducting composites based one-dimensional nanofiber devices offer advantages over conventional spin-coated thin films and provide a simple strategy for producing high-performance FET devices.

Synthesis of Oligosaccharide-Based Block Copolymers with Pendent π-Conjugated Oligofluorene Moieties and Their Electrical Device Applications

Abstract: We report the synthesis and electric device applications of oligosaccharide-based diblock copolymers consisting of a maltoheptaose (MH) block and a poly(4-oligofluorenylstyrene) block (PStFln, n = 1 or 2), referred to as MH-b-PStFln. MH-b-PStFln was prepared by the Cu(I)-catalyzed click reaction of azido-terminated PStFln (PStFln-N3), which was obtained from the azidation reaction of the bromo-terminated PStFln (PStFln-Br), with excess ethynyl-terminated MH in the THF/DMF mixture solvent. The resulting diblock copolymers self-assembled to spherical microdomains with sub-10 nm sizes in both bulk and thin film state after annealing process. Thereafter, the MH-b-PStFln thin film (∼50 nm) with the self-assembled nanoscale spherical aggregates was used as the charge storage layer for the pentacene-based field-effect transistor type memory devices. The MH-b-PStFln-based devices had the excellent hole mobility (0.25–0.52 cm2 V–1 s–1) and the high ON/OFF current (ION/IOFF) ratio of 107–108, of which the MH-b-PStF...

Nonvolatile memories using the electrets of conjugated rod-coil block copolymer and its nanocomposite with single wall carbon nanotubes

Abstract: We report high performance pentacene based organic field-effect transistor (OFET) memory devices using the electrets of conjugated rod-coil block copolymers, poly[2,7-(9,9-dihexylfluorene)]-block-poly(stearyl acrylate) (PF-b-PSA) and their nanocomposites with single-wall carbon nanotubes (SWCNT). The self-assembled PF-b-PSA electret, with the PF nanorods covered by the crystalline PSA block, exhibited a distinct hole-trapping capability due to the high electrical field generated in the confined dimension of the nanorods. Thus, it could effectively reduce the current leakage and stabilize data retention with a large memory window (35.8 V) and a high ON/OFF ratio over 104 s. Furthermore, the memory window of the device was further improved to 49.2 V by wrapping well-dispersed single-wall carbon nanotubes (SWCNT) in PF-b-PSA. The bundles of PF nanorods along the SWCNT effectively capture electrons and maintain retention characteristics similar to that of the PF-b-PSA device. This study demonstrated that the self-assembled conjugated rod-coil block copolymers and their nanocomposites could act as charge-storage electrets for high performance OFET memory devices through the precise morphology control.

Synthesis of monodispersed polystyrene–silver core–shell particles and their application in the fabrication of stretchable large-scale anisotropic conductive films

Abstract: Monodispersed core–shell conductive particles are designed and produced as efficient electron transporting materials for anisotropic conductive films. Traditionally, particle size control was required usually owing to the demand of anisotropic conductive films. Here, an innovative and facile method is proposed to prepare large-scale anisotropic conductive films by incorporating organic–inorganic core–shell conductive particles. First of all, monodispersed polystyrene–silver (PS–Ag) core–shell particles were prepared by emulsifier-free emulsion polymerization and a modified electroless plating process. A series of variables were used to synthesize the PS–Ag conductive particles to enhance the mobility of electrons in a given medium. The resulting PS–Ag conductive particles had excellent bulk conductivity with Ag nanoshells compactly embedded on the surface of PS colloids. In addition, the PS–Ag conductive particles were further mixed with soft latex particles of poly(styrene-co-butyl acrylate), P(St–BA), and then followed by the film-forming process. After the formation of large-scale anisotropic conductive films by the gravity sedimentation method, a remarkable flexible behavior with good conductivity was obtained. The presented method shows the significance of developments in electronic fields and is expected to be a practical, facile, and general approach for the fabrication of anisotropic conductive films with good flexibility and stretchability.

Biaxially Extended Conjugated Polymers with Thieno[3,2-b]thiophene Building Block for High Performance Field-Effect Transistor Applications

Abstract: Biaxially thiophene side chain extended thieno[3,2-b]thiophene (TT2T)-based polymers, PTTT2T, P2TTT2T, PTTTT2T, and PTVTTT2T, were synthesized by Stille coupling polymerization with different conjugated moieties of thiophene (T), bithiophene (2T), thieno[3,2-b]thiophene (TT), and thiophene–vinylene–thiophene (TVT), respectively. The electronic properties of the prepared polymers could be effectively tuned because the variant π-conjugated building block affected the backbone conformation and the resulted morphology. The morphology of the thin films characterized by atomic force microscopy and grazing incidence X-ray diffraction showed that P2TTT2T and PTVTTT2T thin films possessed a better molecular packing with a nanofiber structure owing to their coplanar backbone. The average field-effect mobilities of PTTT2T, P2TTT2T, PTTTT2T, and PTVTTT2T were 6.7 × 10–6, 0.36, 2.2 × 10–3, and 0.64 cm2 V–1 s–1 (maximum 0.71), respectively, attributed to the coplanarity of polymer skeleton. In addition, the fabricated ...

High Sensitivity $17~\mu \text{m}$ Pixel Pitch $640\times 512$ Uncooled Infrared Focal Plane Arrays Based on Amorphous Vanadium Oxide Thin Films

Abstract: This letter presents a $17~\mu \text{m}$ pixel pitch $640\times 512$ uncooled infrared focal plane arrays based on the double sacrificial layer microbolometer technology incorporating amorphous vanadium oxide thin film and frequency selective structure The amorphous vanadium oxide thin-film features low-noise and high-thermal coefficient of resistance characteristics, which help to improve the radiometric performance of the microbolometer By incorporating a frequency selective second platform, the responsivity of the microbolometer was improved by nearly 30% over $8\sim 14\mu \text{m}$ spectra band Noise equivalent temperature difference of less than 35 mK was obtained at 300 K ambient temperature with f/10 optics

Effect of Clay Types on the Properties of Silane Compatibilzied Metallocene Polyethylene/Clay Nanocomposites:

Abstract: The interaction between the intercalant within clay and the compatibilizer is essential to the properties of nanocomposites, and the compatibilizer properties are often neglected. In this work, we ...

Intelligent Synchronous Control via Self-Tuning PID Controller for Gantry Position Stage

Abstract: An intelligent synchronous control via self-tuning proportional-integral-derivative (PID) controller is proposed in this study for the precision contours tracking of a gantry position stage. First, a Lagrangian equation based 3-DOF dynamic model for the gantry position stage is derived. Then, to achieve accurate trajectory tracking performance with robustness, an intelligent control approach using self-tuning PID is proposed for the gantry position stage. In the proposed approach, the on-line learning algorithms of the self-tuning PID are derived using back-propagation (BP) method to guarantee the convergence of the network. Finally, some experimental results of the gantry position stage for optical inspection application are obtained to show the validity of the proposed control approach.

Method for producing patterned metal nanowires, electrode using the patterned metal nanowires, and transistor using the patterned metal nanowire electrode

Abstract: The present invention relates to a method of producing patterned silver nanowire, comprising: coating a photosensitive polyamide acid polymer solution on a silica substrate and dried; using a photomask to paste on the photosensitive polyamic acid and illuminates by ultraviolet; using a developer to obtain a patterned polyamide acid template; coating a metal nanowire suspension on the patterned template; and removing the metal nanowire outside of the patterned polyamic acid. The present invention also discloses an electrode using the patterned metal nanowire and a transistor using the patterned metal nanowire electrode.

Nanofiber and photovoltaic device comprising patterned nanofiber

Abstract: This invention provides a nanofiber, including: a core, which extends along the axis of the nanofiber, and its main component includes Ag(NH3)2 + or AgNO3; a shell, which extends along the nanofiber and coats the core of the nanofiber, and its main component of the shell structure includes: PVP, TBAP, SDS, grapheme, PMAA or PFBT nanoparticle. Moreover, the invention also provides a photovoltaic device which comprises the patterned nanofibers.