Poly Phenylene Vinylene Derivatives Research Articles

Hybrid White Organic Light Emitting Diodes Using Dual Core Blue Fluorescent Emitter.

White OLED (WOLED) devices were fabricated using blue emitting materials, TP-AA-TP, TP-AA-TPB, and TPB-AA-TPB, and yellow emitting material polyphenylenevinylene derivative (PDY 132). Three devices were fabricated with the following structure: ITO/PEDOT:PSS (50 nm)/PDY-132 (40 nm)/NPB (10 nm)/Blue EML (30 nm)/Alq₃ (20 nm)/LiF (1 nm)/Al (200 nm). PDY-132 was used by spin coating, and then three blue fluorescent materials were used by vapor deposition to form a white light emitting device. The color coordinates of WOLED using TP-AA-TP, TP-AA-TPB and TPB-AA-TPB were (0.291, 0.317), (0.317, 0.371) and (0.345, 0.457), respectively. Device using TP-AA-TP as blue emitting material showed the highest efficiencies at 10 mA/cm², L.E of 5.58 cd/A, P.E of 2.16 lm/W and E.Q.E of 2.96%.

The piezoresistance of a device with polyphenylenevinylene derivative PSS-PPV film

The mechanical and electrical characteristics of poly[1-methoxy-4-(3-propyloxy-heptaisobutyl-PSS)-2,5-phenylenevinylene] (PSS-PPV) film were studied in this work. The loading curves and Young’s modulus of PSS-PPV film were measured with nanoindentation tests. The device ITO/PSS-PPV (75 nm)/Al (100 nm) was fabricated and measured to obtain the current–voltage (I–V) and current-time (I–T) curves under different pressures ranging in 0–163 kPa. The device demonstrated high sensitivity, good stability, and nice repeatability. The piezoresistance coefficient can even reach 2.0 × 10−3 Pa−1 at 0.2 V and 111 kPa. The time and charges required to form a stable build-in electric field in the device under different pressures were analyzed using a high-frequency square-wave voltage. It is deduced that the applied pressure not only tightens the PSS-PPV film but also improves its conductance. This property makes PSS-PPV film possess prospect in pressure sensing applications, though it still suffers from partly slow recovering after considerable compression.

Highly Efficient White Organic Light Emitting Diodes Using New Blue Fluorescence Emitter.

Two different emitting compounds, 1-[1,1';3',1"]Terphenyl-5'-yl-6-(10-[1,1';3',1"]terpheny-5'-yl- anthracen-9-yl)-pyrene (TP-AP-TP) and Poly-phenylene vinylene derivative (PDY 132) were used to white OLED device. By incorporating adjacent blue and yellow emitting layers in a multi-layered structure, highly efficient white emission has been attained. The device was fabricated with a hybrid configuration structure: ITO/PEDOT (40 nm)/PDY-132 (8-50 nm)/ NPB (10 nm)/TP-AP-TP (30 nm)/Alq3 (20 nm)/LiF (1 nm)/Al (200 nm). After fixing TP-AP-TP thickness of 30 nm by evaporation, PDY-132 thickness varied with 8, 15, 35, and 50 nm by spin coating in device. The luminance efficiency of the white devices at 10 mA/cm2 were 2.93 cd/A-6.55 cd/A. One of white devices showed 6.55 cd/A and white color of (0.290, 0.331).

Influence of the Temperature as an Environmental Factor on the Electrophysical Behavior of Flexible Polymeric Luminescent Devices

The effect of operational temperature on the electrophysical properties of polymer based electroluminescent structures is examined. For this purpose thin film of light-emitting semiconductor polyphenylenevinylene derivative is deposited between two indium-tin oxide (ITO) electrodes. DC current-voltage (I-V) characteristics of the fabricated devices ITO/polyphenylenevinylene derivative PPV-D/ITO are measured at varying ambient temperatures, ranging from room temperature (25°C) to 70°C. Several important electrical parameters like a trap factor, traps activation energy distribution, free carriers’ density, trapped carriers density, and effective mobility are estimated from measured temperature dependent I-V curves. Such analysis of the charge transport process in polymer devices may give information needed for optimization of the existing structures.

The Synthesis and Characterization of Polyphenylene Vinylene (PPV) Derivatives with Alkoxy Branched Chains

Polyphenylene vinylene derivatives with various alkoxy branched chains, including PMOBOPV,PMOCOPV,iso-PMOCOPV and PMODOPV,were synthesized via a dehydrochlorination route,and characterized by FTIR,HNMR,DSC,TGA,UV-Visible and fluorescence spectroscopy. The result indicated that as-prepared polymers were of remarkable thermal stability and solubility in common solvent with the maximum UV absorption peak at ~492nm and light emission at ~555 nm.

Water-soluble PPV and C60 nanocomposite with enhanced miscibility and enhanced photo-induced charge transfer through ground state electrostatic interactions

We report the preparation of highly charged nanocomposites comprised of water-soluble, anionic fullerene and cationic poly-phenylenevinylene (PPV) derivatives. The nanocomposites display high fluorescence quenching efficiency (99%) presumably due to enhanced miscibility between cationic PPV and anionic C60 via electrostatic interactions. We show that complexation between the cationic PPV and anionic C60 derivatives leads to formation of nanocomposites with optical and electronic properties distinct from individual components without preferential electrostatic interactions. Photo-induced charge transfer quenches fluorescence from the PPV component is consistent with the frontier energy offsets of PPV and C60, and cyclic voltammetry and UV–Vis spectroscopy measurements. This result confirms high miscibility between donor and acceptor and resonance Raman spectra indicate a conformational changes of the PPV backbone upon complex formation.

Transient absorption study on the influence of several polyphenylene vinylene derivatives on the exciton lifetimes in lead(II) sulfide quantum dots

The aim of this Letter is to show the influence of several new polyphenylene vinylene (PPV) derivatives, covering surfaces of lead(II) sulfide semiconductor quantum dots, on optical properties of nanocrystals, especially on exciton lifetimes. The collected data exhibit strong dependence of the excited states lifetimes in PbS nanocrystals on the distance between the polymer chain and the quantum dot. It turns out that the presence of PPV derivatives stabilizes the created exciton, which is manifested by the increase of its lifetime. Anyway this effect weakens in PPV derivatives with longer side chains separating nanocrystal from the main conductive chain.

Observation of the missing mode effect in a poly-phenylenevinylene derivative: Effect of solvent, chain packing, and composition

Optical emission spectra of poly[2-methoxy-5-[3('),7(')-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) in dilute solutions exhibit a vibronic progression interval (∼1225 cm(-1)) that does not correspond to any ground state vibrational mode frequency. This phenomenon is assigned as the missing mode effect (MIME) in which five key displaced polymer backbone vibrational modes in the range of 800-1600 cm(-1) contribute to the MIME interval. Emission spectra are calculated by analytically solving the time-dependent Schrödinger equation using estimates of mode-specific vibrational displacements determined independently from preresonance Raman intensities. Emission spectra of MDMO-PPV thin films and nanoparticles are measured and lineshapes show an increase of the MIME frequency to ∼1340 cm(-1) in addition to changes in vibronic intensity distributions and energies. Composite blend thin films consisting of MDMO-PPV and a fullerene derivative (1:1 w/w) exhibit a substantially larger MIME interval (∼1450 cm(-1)) that arises from an increase in polymer chain planarity. This structural change is most apparent from large decreases of the excited state displacement of an out-of-plane C-H bending mode (961 cm(-1)) that becomes forbidden in the planar structure.

Improvement of the electrical characteristics of polymer electroluminescent structures by using spray-coating technology

In this article, polyphenylenevinylene derivative (poly(9,9-dihexyl-9H-fluorene-2,7-diyl-vinylene)) (PPV-D) thin films were deposited by spray deposition and spin-coating. Film morphology was investigated by scanning electron microscopy images and surface profile diagrams. The traps concentration depending on the deposition method was evaluated based on current–voltage characteristics of ITO/PPV-D/Al structures measured at different temperatures. Brightness–voltage characteristics of the structures containing spray deposited and spin-coated PPV-D films with the same thickness were measured. The film surface at spray deposition tends to be uniform and smoother than the spin-coated one. The structure with sprayed polymer layer showed higher maximal trap factor (0.94 × 10−3 vs 0.83 × 10−3 for spin-coating), which is evidence for less defects in the bulk and presence of more free carriers, contributing to the conduction and the radiative recombination. Twice-higher luminance and 1.4 V lower turn-on voltage were achieved, using spray deposition in comparison with the spin-coating technique. The spray technique for polymer deposition is a very powerful tool for the preparation of cost effective organic-based devices with improved electrical characteristics and efficiency.

Photosensitive in wide spectral region composites based on polyphenylenevinylene

Abstract. Optical and photovoltaic properties of polyphenylenevinylene derivative – poly(2-methoxy-5-(3-,7-dimethyl-octyloxy)-1,4-phenylenevinylene (MDMO-PPV) and its composites with high (40 %) concentration polymethine dyes (PD) – meso-Cl and hexaindoletricarbocyanine (HITC) films have been studied. Two H-aggregates of dyes with different energies that weakly depend on the molecular structure of dyes, is formed in MDMO-PPV with PD in composites films. The efficiency of photogeneration of charge carrier by these aggregates is greater than the efficiency of photogeneration of charge carriers by the quasi-isolated molecules of dye. It results in substantial expansion of the absorption region (in comparison with the absorption region of molecules in solution) and photosensitivity in the side of higher energies. The presence of PD aggregates in the films MDMO-PPV influences on their photosensitivity that depends on PD molecular structure. This dependence can be caused by interaction between the molecules of MDMO-PPV and dye. In composites MDMO-PPV/HITC, the value of interaction is low and practically does not influence the efficiency of photogeneration of charge carriers by MDMO-PPV molecules, which give a considerable contribution to formation of the photovoltage in 2-3 eV regions. The interaction of meso-Cl and MDMO-PPV molecules is stronger, and this, probably, results in considerable decrease of photovoltage in the region of the excitation of MDMO-PPV.

Influence of Interchain and Self Intrachain Aggregations on Photoluminescence of a Poly-Phenylenevinylene Derivative

A poly-phenylenevinylene derivative(poly(2,5-dioctyloxy) -p-phenylene vinylene) (DOO-PPV) with a high degree of physical crosslinking(designated the gelation of DOO-PPV) was synthesized and characterized. Analyses of the Fourier transform-infrared(FT-IR) and the Fourier transform-Raman(FT-Raman) spectra indicate that the chemical structure of the gelation of DOO-PPV is accordant with short chain linear molecule of DOO-PPV. Photoluminescence spectra of a thin film,short chain linear molecule,and solid gelation show that the ratio of the intensity at the short wavelength emitting band and at the long wavelength emitting band decreases gradually,the ratio is 3.24,1.10 and 0.47,respectively. Analysis of X-ray diffraction(XRD) indicated that the existence of a more oriented structure in the gelation of DOO-PPV compared with the short chain molecule and the thin film. This result suggests that interchain and self intrachain aggregations play an important role in the photoluminescence.

Correlation between Dielectric/Organic Interface Properties and Key Electrical Parameters in PPV-based OFETs

We report on the influence of the dielectric/organic interface properties on the electrical characteristics of field-effect transistors based on polyphenylenevinylene derivatives. Through a systematic investigation of the most common dielectric surface treatments, a direct correlation of their effect on the field-effect electrical parameters, such as charge carrier mobility, On/Off current ratio, threshold voltage, and current hysteresis, has been established. It is found that the presence of OH groups at the dielectric surface, already known to act as carrier traps for electrons, decreases the hole mobility whereas it does not substantially affect the other electrical characteristics. The treatment of silicon dioxide surfaces with gas phase molecules such as octadecyltrichlorosilane and hexamethyldisilazane leads to an improvement in hole mobility as well as to a decrease in current hysteresis. The effects of a dielectric polymer layer spin coated onto silicon dioxide substrates before deposition of the semiconductor polymer can be related not only to the OH groups density but also to the interaction between the dielectric and the semiconductor molecules. Specifically, the elimination of the OH groups produces the same effect observed with hexamethyldisilazane. The hole mobility values obtained with hexamethyldisilazane and polymer dielectrics are the highest reported to date for PPV-based field-effect transistors.

High performance light emitting transistors

Solution processed light emitting field-effect transistors (LEFETs) with peak brightness exceeding 2500cd∕m2 and external quantum efficiency of 0.15% are demonstrated. The devices utilized a bilayer film comprising a hole transporting polymer, poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b] thiophene) and a light emitting polymer, Super Yellow, a polyphenylenevinylene derivative. The LEFETs were fabricated in the bottom gate architecture with top-contact Ca∕Ag as source/drain electrodes. Light emission was controlled by the gate voltage which controls the hole current. These results indicate that high brightness LEFETs can be made by using the bilayer film (hole transporting layer and a light emitting polymer).

Conjugated Polymer-Based Organic Solar Cells

The need to develop inexpensive renewable energy sources stimulates scientific research for efficient, low-cost photovoltaic devices.1 The organic, polymer-based photovoltaic elements have introduced at least the potential of obtaining cheap and easy methods to produce energy from light.2 The possibility of chemically manipulating the material properties of polymers (plastics) combined with a variety of easy and cheap processing techniques has made polymer-based materials present in almost every aspect of modern society.3 Organic semiconductors have several advantages: (a) lowcost synthesis, and (b) easy manufacture of thin film devices by vacuum evaporation/sublimation or solution cast or printing technologies. Furthermore, organic semiconductor thin films may show high absorption coefficients4 exceeding 105 cm-1, which makes them good chromophores for optoelectronic applications. The electronic band gap of organic semiconductors can be engineered by chemical synthesis for simple color changing of light emitting diodes (LEDs).5 Charge carrier mobilities as high as 10 cm2/V‚s6 made them competitive with amorphous silicon.7 This review is organized as follows. In the first part, we will give a general introduction to the materials, production techniques, working principles, critical parameters, and stability of the organic solar cells. In the second part, we will focus on conjugated polymer/fullerene bulk heterojunction solar cells, mainly on polyphenylenevinylene (PPV) derivatives/(1-(3-methoxycarbonyl) propyl-1-phenyl[6,6]C61) (PCBM) fullerene derivatives and poly(3-hexylthiophene) (P3HT)/PCBM systems. In the third part, we will discuss the alternative approaches such as polymer/polymer solar cells and organic/inorganic hybrid solar cells. In the fourth part, we will suggest possible routes for further improvements and finish with some conclusions. The different papers mentioned in the text have been chosen for didactical purposes and cannot reflect the chronology of the research field nor have a claim of completeness. The further interested reader is referred to the vast amount of quality papers published in this field during the past decade.

Fractions of singlet and triplet excitons generated in organic light-emitting devices based on a polyphenylenevinylene derivative

The effect of magnetic field on the intensity of electroluminescence from devices made of a poly-$p$-phenylenevinylene (PPV) copolymer was investigated. The emission intensity was enhanced by the application of magnetic field, and the magnitude of the increase depended on operational voltages. When the device was operated under application of low voltages, the intensity increased with magnetic field and reached an 8.5% increase at about $100\phantom{\rule{0.3em}{0ex}}\mathrm{mT}$. With the increase of the operational voltage, the effect of magnetic field was lessened. In addition, when measured at high voltages with increasing magnetic field, the emission intensity started to decrease after passing a maximum, then leveled off. This saturation value was slightly higher than that observed in the absence of magnetic field. These findings suggest that two processes sensitive to magnetic field are included in the emission processes. They are assigned to the charge recombination (CR) of anion and cation radicals and triplet-triplet annihilation (TTA) processes. From the analysis of the effects of magnetic field on the emission intensity based on a kinetic model, we quantitatively determined the fractions of singlet and triplet excitons generated through the CR process to be 0.17 and 0.83, respectively. With the increase of the concentration of triplet excitons in the organic layer, production of singlet excitons through the TTA process was enhanced, and the total yield of the singlet excitons exceeded 0.5 under normal device operational conditions. We conclude that this high yield is responsible for the high emission efficiency observed in the light-emitting devices based on PPVs.

Sunlight stability of organic light-emitting diodes

This paper reports on the photodegradation of organic light-emitting diodes (OLEDs) due to exposure to visible and near-ultraviolet light. Such exposure affects strongly the device performance, e.g., the electroluminescence intensity and the device current decrease considerably, however, the photoluminescence remains unaffected. This photodegradation was investigated on various production-relevant classes of high-quality polymer semiconductors with different energy gaps, i.e., a yellowish-green polyphenylenevinylene derivative, a red polyfluorene derivative, and a blue polyspiro derivative. It will be demonstrated that the action spectrum of the photodegradation is strongly correlated with the fundamental absorption of the polymer itself. The indium-doped tin oxide (ITO) polymer interface was identified as the interface where photodegradation takes place, while the bulk of each layer (ITO or polymer) turned out to be insensitive to irradiation with visible or near-ultraviolet light. Furthermore, it is demonstrated that the photoinduced damage can be suppressed by inserting appropriate interlayer systems.

Fabrication of a composite nano-ultrathin film of poly-phenylene-vinylene and C 60 derivative

The monolayers of pure C 60 derivative (C60-COOH) are stable on the surface of pure water subphase and poly-phenylene-vinylene derivative (PPV) solution, respectively. The composite ultrathin film of PPV and C60-COOH was successively fabricated on the quartz and mica substrate by using Langmuir–Blodgett technique. X-ray photoelectron spectrometry (XPS) measurements show that the PPV is embedded into the film during the fabrication process. The surface morphologies of pure C60-COOH film and the composite film were investigated with atomic force microscopy (AFM), respectively. The phenomenon of electron transmission between PPV and C60-COOH in the composite film was confirmed by UV–vis spectra.

Geometric constraints in the growth of nanotube-templated polymer monolayers

We present a simple and general model that describes the ordered assembly of polymer strands on nanotube surfaces. Energetically favorable coiling angles are identified based on geometric constraints that limit the maximum coverage of polymers on the walls of the nanotubes. The coiling angles can be controlled by selecting the appropriate nanotube diameters, opening the possibility of engineering the strength of composite fibers. The model is applied to two different polymeric molecules; namely, polyacetylene and a polyphenylenevinylene derivative.

Solar cells from thermally treated polymer/dye blends with good spectral coverage

We report a new photovoltaic material combination that comprises a blend of two conjugated polymers with a molecular dye. The constituents were chosen in order to achieve a wide spectral response. The polymer poly(9,9-bis(2-ethylhexyl)fluorene-2,7-diyl) (PF 2/6) was blended with a polyphenylenevinylene derivative, Covion Super Yellow™ (SY), and violanthrone to produce a broad spectral response covering a large part of the visible spectrum. Annealing at 200 °C in air leads to a roughly three-fold improvement in external quantum efficiency (EQE) and produces a structure with >1% EQE at all wavelengths between 350 and 650 nm.

SEPARATE-COATING AND LAYER-BY-LAYER DEPOSITION OF POLYMER EMITTING MATERIALS BY THE SPRAY DEPOSITION

The spray deposition method has been developed as a new way of polymer ultra-thin film preparation for organic optoelectronic devices such as an organic light emitting diode (OLED). In this method, a highly diluted solution of an organic material is nebulized into air and concentrated under a controlled evaporation condition. The resulting aerosol is transported by a carrier gas and deposited onto a solid substrate. This method has substantial advantages that an almost insoluble and non-evaporative material can be fabricated into a thin film, and that a separate-coating and layer-by-layer deposition of polymer materials can be performed. An OLED was prepared from highly diluted THF solutions (10−4 wt%) of two poly-phenylenevinylene derivatives. One shows red emission and the other green. The red polymer was deposited on an ITO electrode through a shadow mask with round holes and 0.1 mm line width to result a fine separate-coating and the green one was laminated onto the patterned film. An Al anode was deposited on the polymer film in a vacuum evaporator. The fabricated OLED showed a patterned emission at around 10 V.