Solution-processed Poly Research Articles

Biocompatible poly(vinylidene fluoride)/cyanoacrylate composite coatings with tunable hydrophobicity and bonding strength

Biocompatible composite coatings are produced from solution processable poly(vinylidene fluoride)/cyanoacrylate blends prepared in the presence of rosin and ZnO particle fillers, the latter for control of coating surface microstructure. Dispersions are spray coated and cured at 100 °C onto aluminum foils and fiberglass cloths suitable for tissue engineering applications. The elastic modulus of the composite films matches or exceeds that of polyethylene-based orthopedic implant materials. Contact angle measurements on coated fiberglass cloths reveal that wettability of hydrophobic coatings is maintained under strain for applied mechanical stress levels up to ∼15 kN/m2, whereas ultrahydrophobic coatings fail at ∼5 kN/m2.

Aggregation and Gelation Effects on the Performance of Poly(3-hexylthiophene)/Fullerene Solar Cells

Poly(3-hexylthiophene) formed gels and showed liquid crystalline structures at high concentrations. The absorption properties of poly(3-hexylthiophene) showed dramatic changes during gelation, which is an indication of strong intermolecular π-electronic coupling of the ordered self-assembled poly(3-hexylthiophene) gels. The effect of conformational transitions on the photovoltaic properties of solution-processed poly(3-hexylthiophene)/fullerene blends has been studied in this Article. It is shown that the photovoltaic performance is strongly affected by gelation, which alters the morphology of the photoactive layer. Device optimization yields solar cells with a power conversion efficiency of 3.78% under standard test conditions (AM 1.5, 100 mW/cm2).

Tetraalkoxylated-PPV derivative: An efficient and pure green electroluminescent polymer with good solution processability

A new solution-processable tetraalkoxy-substituted poly(1,4-phenylenevinylene) derivative, poly{[2-(3′,7′-dimethyloctyloxy)-3,5,6-trimethoxy]-1,4-phenylenevinylene} (TALK-PPV), was synthesized through a dehydrohalogenation polymerization route, and its light-emitting properties were investigated. The TALK-PPV showed highly blue-shifted UV–visible absorption and PL emission spectra compared to the dialkoxy-substituted PPV derivatives. This is because of the disturbance to the π-conjugation caused by a steric hindered structure. The TALK-PPV thin film exhibited an absorption peak at 446nm, with an onset at 515nm. Its PL emission maximum was at 554nm. Cyclic voltammetric analysis showed the HOMO and LUMO energy levels of the TALK-PPV to be 5.77 and 3.36eV, respectively. Light-emitting devices were fabricated with an ITO (indium-tin oxide)/PEDOT/polymer/Ca/Al configuration. The TALK-PPV component leads to pure green light emission with a CIE 1931 chromaticity of (0.20, 0.74) at 100cd/m2 brightness, which is very close to the standard green (0.21, 0.71) demanded by the NTSC (National Television System Committee). The maximum brightness of this device was 24,900cd/m2 with an efficiency of 1.45cd/A.

Supramolecularly Assembled Hybrid Materials via Molecular Recognition between Diaminopyrimidine-Functionalized Poly(hexylthiophene) and Thymine-Capped CdSe Nanocrystals

A solution processible poly(3-hexylthiophene) derivative containing O4-substituted diaminopyrimidine (ODAP) terminated side groups has been prepared by post-polymerization functionalization of the precursor copolymer, namely, regioregular poly(3-hexylthiophene-co-3-(6-bromohexyl)thiophene), with 2,4-diamino-6-hydroxypyrimidine. An interesting feature of this polymer is its capability of the hydrogen bond assisted formation of organic−inorganic composites with 1-(6-mercaptohexyl)thymine functionalized semiconductor nanocrystals (CdSe). The composites, obtained in a simple one-pot preparation step, exhibit a homogeneous distribution of nanocrystals within the polymer matrix in an extended three-dimensional network, whereas in blends without specific interaction between the constituents, phase segregation on a submicron level occurs.

Enhanced performance of solution-processed regioregular poly(3-hexylthiophene) thin-film transistors using planar bottom-contact architecture

The authors report on the solution-processed planar bottom-contact (pBC) organic thin-film transistors and contact effect on gate threshold voltage incorporating regioregular poly(3-hexylthiophene) active layer. By employing pBC configuration, the transistors on SiO2∕Si without surface modification show much higher mobility, lower threshold voltage, and narrower dispersion of threshold voltage when compared to the conventional bottom-contact counterparts. The high mobility and lower threshold voltage are attributed to an improved contact at the interface between the source/drain electrodes and the poly(3-hexylthiophene) active layer.

Synthesis and Characterization of Poly(N-arylcarbazole-alt-aniline) Copolymers as Blue-Emitting Host Matrix for Polymer Light-Emitting Diodes

Thermally stable and solution-processable poly(N-arylcarbazole-alt-aniline) copolymers with high structural integrity were synthesized in good yields via palladium-catalyzed polycondensation of aniline with corresponding N-arylcarbazole monomers such as N-(2-ethylhexyloxyphenyl)-3,6-dibromocarbazole, bis[6-bromo-N-(2-ethylhexyloxyphenyl)carbazole-3-yl] and N-(4-(2-ethylhexyl)-3,5-dibromomethylene-phenyl)carbazole, respectively. The optical and electrochemical properties of these copolymers were measured and compared with those of poly(N-alkylcarbazole-alt-aniline) copolymer. All synthesized poly(N-arylcarbazole-alt-aniline) copolymers showed maximum UV-Vis absorption peaks at around 300 nm in THF solution, and exhibited maximum photoluminescence peaks in the blue emission range from 430 to 460 nm. It was also found that poly(N-arylcarbazole-alt-aniline) copolymers had wider band gap energy than poly(N-alkylcarbazole-alt-aniline) copolymer.

Threshold-voltage tuning characteristics of all-organic electrochemical vertical rectifiers on flexible substrates

A printed all-organic electrochemical vertical tunable rectifier is demonstrated using a conducting polymer as the active material on a flexible plastic substrate. Solution processable poly(3,4-ethylenedioxythiophene) combined with poly(styrene sulfonic acid) (PEDOT:PSS) was coated on polyester film; the rectifier channel was patterned on the PEDOT:PSS film through directly writing technique without the need for masks, patterns, or dies. A vertically layered electrochemical cell was structured via printing and laminating processes to reduce driving voltages. The resulting rectifier is a three-terminal device; the functionality of threshold voltage tuning is realized by adjusting the potential difference within the electrochemical cell. The driving voltages are reduced significantly compared to rectifiers with lateral device architecture. In a single device, the threshold voltage is tunable between 0.16 and 1.0 V while a bias voltage is swept from 0.9 to 1.7 V.

10.5L: Late-News Paper: All-Organic TFT-Driven QQVGA Active-Matrix Polymer-Dispersed LCD with Solution-Processed Insulator, Electrodes, and Wires

A high-performance pentacene organic-TFT backplane with a solution-processed novel poly(4-vinylphenol)-based dielectric and a solution-processed organo-silver electrode/wire has been developed below 150°C. The all-organic-TFT backplane has been successfully applied to drive a QQVGA active-matrix (AM) polymer-dispersed (PD) LCD with a resolution of 79 dpi and a display size of 2.5 inches.

Conjugated Polymers Containing Large Soluble Diethynyl Iptycenes

[structures: see text] An efficient synthesis of large iptycenes appended with alkoxy and ethynyl substituents is reported. The rigid shape-persistent iptycene scaffold prevents interactions between the polymer backbones and can be used to solubilize polymers containing less soluble but readily accessible comonomers to prepare functional, solution-processible poly(p-phenyleneethynylene) (PPE)-conjugated polymers. These polymers are highly emissive in thin films without significant excimer/exciplex formation as a result of the effective chain isolation enforced by the iptycene units.

Poly(3,3‘ ‘-dialkylterthiophene)s: Room-Temperature, Solution-Processed, High-Mobility Semiconductors for Organic Thin-Film Transistors

Most solution-processed organic semiconductors for organic thin film transistor applications require high-temperature annealing and/or fabrication in an inert atmosphere to achieve high mobility. Solution-processed poly(3,3‘ ‘-dialkylterthiophene) 3 was found to provide functionally useful transistor properties even when fabricated at room temperature under ambient conditions.

Dopant density determination in disordered organic field-effect transistors

We demonstrate that, by using a concentric device geometry, the dopant density and the bulk charge-carrier mobility can simultaneously be estimated from the transfer characteristics of a single disordered organic transistor. The technique has been applied to determine the relation between the mobility and the charge density in solution-processed poly(2,5-thienylene vinylene) and poly(3-hexyl thiophene) thin-film field-effect transistors. The observation that doping due to air exposure takes place already in the dark, demonstrates that photoinduced oxygen doping is not the complete picture.

Synthetic Routes to Solution-Processable Polycyclopentadithiophenes

Three synthetic protocols have been employed to prepare solution-processable poly(4,4-dialkylcyclopentadithiophenes). These polymers are fused-ring analogues of poly(3-alkylthiophenes) and structural analogues of the polyfluorenes. Oxidative polymerization of 4,4-dialkylcyclopenta[2,1-b;3,4-b‘]dithiophenes using iron (III) chloride gave high-molecular-weight polymers, whereas nickel-catalyzed polymerization of the 2,6-dibromo derivatives via in situ-generated thienylmagnesium and thienylzinc reagents gave moderate-molecular-weight polymers. The structures of the polymers were confirmed by NMR spectroscopy and MALDI-TOF mass spectrometry. In the polymerization using organomagnesium intermediates, some chain capping by methyl end groups was observed. This side reaction can be avoided by polymerization of the organozinc reagents. Post-functionalization of the halogen termini of these polymers can be readily achieved using a cross-coupling with an aryl Grignard reagent. The main chain conjugation in these polymers can be directly correlated to the length of the polymer backbone because the UV−vis spectra of fractionated samples show absorption maxima that increase with the average degree of polymerization as determined by GPC, up to a limiting value of ∼20. UV−vis spectroscopy suggests that poly(4,4-dialkylcyclopentadithiophenes) do not self-assemble in the solid state, as has been previously observed for regioregular poly-3-alkylthiophenes.

Emission characteristics of two-polymer layer electroluminescent devices operating under various duty cycles

We report the emission characteristics of two-polymer layer electroluminescent devices, fabricated from poly( p-phenylenevinylene) and a solution-processable poly(cyanoterephthalylidene), driven using pulsed voltages. Current, luminance and response times were measured as a function of drive voltage. A peak pulsed luminance of 10 4 cd m −2 was achieved at a current density of 1.5 A cm −2, with linear variation of light output with current up to this value.

Processable Thiophene Copolymer With A Chiral Amino Acid Side Chain

ABSTRACTConjugated polymers in general, and polythiophenes in particular have been attracting attention in the field of molecular electronics. Polythiophenes functionalized at the β- position with various groups have resulted in processable, conjugated polymeric systems with applications such as organic electrodes, photorefractive materials, electro-luminescent devices, among others. We report the synthesis of a thiophene copolymer with alkyl and chiral amino acid substituents at the β- position. We have synthesized a solution processable poly[3-octylthiophene-co-(N-1-carboxyl, 2- (4-hydroxy-3-nitrophenyl)ethyl)-3-thiophene acetamide] with 3-nitro-L-Tyrosine as the chiral amino acid side chain. The UV-Visible and optical rotatory dispersion spectra of the new copolymer are discussed.

Electrical and mechanical properties of oriented poly(3-alkylthiophenes): 2. Effect of side-chain length

The mechanical and electrical properties of solution-processed poly(3-alkylthiophenes) with alkyl side-chain lengths of 6, 8 and 12 carbon atoms are discussed. Tensile drawing at elevated temperatures yielded oriented materials with moderately increased mechanical properties. A simple model accounting for defects in the regiospecificity, i.e. head-to-tail versus head-to-head or tail-to-tail monomer coupling, is introduced, in addition to side-chain dilution, to account for the low moduli of undoped samples. Doping with FeCl 3 · 6H 2O led to significant enhancement of the mechanical properties of the drawn samples, as well as to high electrical conductivity. As was previously found for other conducting polymer systems, strong correlations were observed between mechanical properties and electrical conductivity. The conductivity was found to scale linearly with tenacity, independent of side-chain length.

Electrical and mechanical properties of oriented poly(3-alkylthiophenes) I. Doping-enhanced stiffness of poly(3-octylthiophene)

The mechanical and electrical properties of solution-processed poly(3-octylthiophene) (P3OT) are presented and discussed. Hot drawing yielded oriented P3OT with moderately improved mechanical properties. Doping with FeCl 3·6H 2O or iodine vapor led to significant enhancement of the stiffness, strength and electrical conductivity of the drawn samples. The increase in stiffness, through the introduction of I 2 vapor, was reversed upon removal of the dopant. As previously found for other conducting polymer systems, strong correlations were observed between mechanical properties and the electrical conductivity.

Thin Films of n -Si/Poly-(CH 3 ) 3 Si-Cyclooctatetraene: Conducting-Polymer Solar Cells and Layered Structures

The optical and electronic properties of thin films of the solution-processible polymer poly-(CH(3))(3)Si-cyclooctatetraene are presented. This conjugated polymer is based on a polyacetylene backbone with (CH(3))(3)Si side groups. Thin transparent films have been cast onto n-doped silicon (n-Si) substrates and doped with iodine to form surfacebarrier solar cells. The devices produce photovoltages that are at the theoretical limit and that are much greater than can be obtained from n-Si contacts with conventional metals. Two methods for forming layered polymeric materials, one involving the spincoating of preformed polymers and the other comprising the sequential polymerization of different monomers, are also described. An organic polymer analog of a metal/insulator/metal capacitor has been constructed with the latter method.

Photoexcited states in poly(3-alkyl thienylenes)

The authors present a comparative study of the properties of two solution-processible alkyl-substituted polythienylenes, poly(3-hexyl thienylene), P3HT and poly(3-dodecyl thienylene), P3DT. Both show the onset of pi - pi * interband absorption at 2 eV with the peak in absorption coefficient near 2.5 eV, and both show strong photoluminescence in an energy band extending from 1.3 to 2 eV. These properties are both due to intra-chain absorption across the pi - pi * gap, with the photoluminescence arising from the radiative decay of the singlet exciton. For the case of P3HT, photoinduced absorption measurements show the presence of two subgap absorption bands, which are associated with the formation of charged bipolarons which require charge separation between chains. P3DT, in contrast, shows a single induced absorption band, at 1 eV, which shows very different temperature and frequency dependence from that of the bipolaron bands in P3HT. The authors consider that a triplet-triplet transition of the triplet intrachain exciton is a possible assignment for this band, and consider that poorer contact between chains in P3DT over that in P3HT inhibits the transfer of charge between chains and thus prevents the formation of charged bipolarons in this polymer. They also discuss the role of the polymer structure in the stabilisation of the photogenerated bipolarons.

Melt and solution processable poly(3-alkylthiophenes) and their blends

We report on the properties of melt and solution processable poly(3-alkylthiophenes), P3AT, and on the fabrication of electrically conducting polymer blends consisting of P3AT, specifically poly(3-octylthiophene), POT, and a thermoplastic matrix polymer made using ordinary melt processing techniques. The POT used in this work was synthesized using two different chemical polymerization techniques. Films made from as-synthesized POT powder, either by solution casting or melt processing techniques were found to be easily doped by electron acceptors to conductivities of 20–30 S/cm. Blending of POT with thermoplastics such as ethylenevinylacetate copolymer, EVA, in the molten state yields polymer blends with excellent mechanical properties that might be doped to conductivities exceeding 1 S/cm.

Processible, environmentally stable, highly conductive forms of polythiophene

As electronic materials, the most promising synthetic semiconductors and metals for practical large scale applications are those which can combine convenient processibility with high environmental stability, good mechanical properties, and high conductivity. Missing from the desired combination of properties for the majority of interesting conductive polymers is convenient processibility. A series of solution processible poly(3-alkylthiophenes) are described which form highly conductive, environmentally stable complexes with electron acceptors. These materials are quite unusual in that, in addition to their attractive properties, conductivities are generally high and surprisingly insensitive to the length of the alkyl substituents.