Indium tin oxide nanoparticles as anode for light‐emitting diodes

Thin films of indium tin oxide (ITO) nanoparticles have been investigated as anode materials for polymer light‐emitting diodes. A luminance efficiency (0.13 cd/A), higher than that (0.09 cd/A) obtained in a control devices fabricated on conventional commercial ITO anodes were found. The thin films were made by spin coating of a suspension followed by annealing. The ITO nanoparticle films have a stable sheet resistance of 200 Ω/sq, and an optical transmittance greater than 86% over the range of 400–1000 nm. Their textural property is also reported. These results demonstrate that ITO nanoparticle can form a high efficient reproducible anode material. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3125–3129, 2006     

Synthesis and properties of fluorenyl–pyridinyl alternatingcopolymers for light‐emitting diodes

A novel series of well‐defined alternating poly[2,7‐(9,9‐di(2‐ethylhexyl)fluorenyl)‐alt‐pyridinyl] (PDEHFP) copolymers were synthesized using palladium(0)‐catalyzed Suzuki coupling reaction in high yields. These polymers were characterized using ¹H NMR, UV‐visible and fluorescence spectroscopies, gel permeation chromatography, thermal analysis and cyclic voltammetry. The optical properties of the copolymers, including photoluminescence (PL) and electroluminescence (EL), were studied. The difference in linkage position of pyridinyl units in the polymer backbone has significant effects on the electronic and optical properties of polymers in solution and in film state. Meta‐linkage (3,5‐ and 2,6‐linkage) of pyridinyl units in the polymer backbone is more favorable for pure blue emission and prevention of aggregation of polymer chains. PDEHFPs with 2,6‐ and 3,5‐linkage of pyridinyl units have relatively high PL efficiency of 37 and 44% in the film state. In comparison with homopolymer PDEHF, the copolymers with pyridinyl units possess low lowest unoccupied molecular orbital energy levels for easy electron injection from a cathode. Strong EL is observed and light‐emitting diodes (LEDs) exhibit typical rectifying characteristics. The emission intensity starts to increase at around 12 V. The emission peak wavelengths of the polymers roughly coincide with those of PL. This series of fluorene–pyridine‐based alternating copolymers seem to be candidates for polymeric LEDs. © 2013 Society of Chemical Industry     

Polylactide‐perylene derivative for blue biodegradable organic light‐emitting diodes

In this work we demonstrate, for the first time, the use of polylactic acid (PLA) as a biodegradable host matrix for the construction of the active emissive layer of organic light‐emitting diode (OLED) devices for potential use in bioelectronics. In this preliminary study, we report a robust synthesis of two fluorescent PLA derivatives, pyrene‐PLA ( AH10 ) and perylene‐PLA ( AH11 ). These materials were prepared by the ring opening polymerisation of l ‐lactide with hydroxyalkyl‐pyrene and hydroxyalkyl‐perylene derivatives using 1,8‐diazabicyclo[5.4.0]undec‐7‐ene as catalyst. OLEDs were fabricated from these materials using a simple device architecture involving a solution‐processed single‐emitting layer in the configuration ITO/PEDOT:PSS/PVK:OXD‐7 (35%): AH10 or AH11 (20%)/TPBi/LiF/Al (ITO, indium tin oxide; PEDOT:PSS, poly(3,4‐ethylenedioxythiophene) doped with poly(styrenesulfonic acid); PVK, poly(vinylcarbazole); OXD‐7, (1,3‐phenylene)‐bis‐[5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole]; TPBi, 2,2′,2″‐(1,3,5‐benzenetriyl)tris(1‐phenyl‐1H‐benzimidazole)). The turn‐on voltage for the perylene OLED at 10 cd m^–2 was around 6 V with a maximum brightness of 1200 cd m^–2 at 13 V. The corresponding external quantum efficiency and device current efficiency were 1.5% and 2.8 cd A^–1 respectively. In summary, this study provides proof of principle that OLEDs can be constructed from PLA, a readily available and renewable bio‐source. © 2020 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.     

Anionic triphenylamine‐ and fluorene‐based conjugated polyelectrolyte as a hole‐transporting material for polymer light‐emitting diodes

BACKGROUND: Hole‐transport layers (HTLs) play a crucial role in multilayer polymeric light‐emitting diodes (PLEDs) for the achievement of satisfactory device performance. During the fabrication of multilayer PLEDs via solution processing, the fabricated HTLs encounter the risk of erosion during the film‐forming process of subsequent emitting layers (EMLs). In contrast to the widely investigated crosslinkable HTLs, much less attention has been paid to the preparation of polar‐solvent‐soluble HTLs, which is a straightforward solution to overcome the interfacial mixing between HTLs and EMLs during solution processing. RESULTS: Alternating triphenylamine‐ and fluorene‐based anionic copolymer poly[9,9‐bis(4′‐sulfonatobutyl)fluorene‐alt‐N‐(p‐trifluoromethyl)phenyl‐4,4′‐diphenylamine]sodium salt (PFT‐CF3) was synthesized via a palladium‐catalyzed Suzuki coupling reaction. This polyelectrolyte is soluble only in polar solvents such as methanol, dimethylformamide and dimethylsulfoxide rather than in non‐polar solvents such as toluene, chloroform and xylene. The relatively high HOMO (?5.22 eV) and LUMO (?2.26 eV) levels of this polymer endow it simultaneously with good hole‐transporting and electron‐blocking capabilities. The performance of red‐, green‐ and blue‐emitting devices utilizing this polyelectrolyte as HTL was investigated. CONCLUSION: The anionic conjugated polyelectrolyte based on triphenylamine and fluorene, PFT‐CF₃, can serve as a promising hole‐transporting/electron‐blocking layer in multilayer PLEDs. Copyright © 2009 Society of Chemical Industry     

Dy and Eu activated Ca3B2O6 phosphors for near ultraviolet‐based light‐emitting diodes

The Dy‐ and Eu‐activated Ca₃B₂O₆ phosphors were synthesized by a high‐temperature solid‐state reaction technique and their structural and luminescent properties were investigated. The phosphors are characterized by X‐ray diffraction, photoluminescence spectra, and Commission International de I'Eclairage (CIE) chromaticity coordinates. It is found that the charge compensator Na⁺ plays an important role in modifying the emission spectral profiles of Dy and Eu ions in the phosphors. The ratio of the emission located at the yellow wavelength portion to that located at the blue wavelength region of the Dy³⁺ ions can be apparently tuned by changing the Na⁺ content. The luminescence intensity of the phosphors can be enhanced with introducing Na⁺ ions as well. The emission colors of Dy/Eu codoped phosphors change from blue to white and successfully acquire the superior white light emission (x = 0.330, y = 0.329) by appropriately tuning the Na⁺/Dy³⁺ content and the excitation wavelength. The energy transfer process from Eu²⁺ to Dy³⁺ and Eu³⁺ occurs in the Dy/Eu codoped phosphors, providing a further approach to modify the emission spectral profile of the examined phosphors. The phosphors presented here have promising applications in the fields of light‐emitting diodes.     

A study of light‐emitting diodes constructed with copolymers having cyclohexyl thiophene and hexyl thiophene units

We report visible light emission from a diode made from copolymers of 3‐alkylthiophenes. These chemically synthesized copolymers exhibit improved electroluminescence and quantum efficiencies compared to poly (3‐cyclohexylthiophene). Good solubility of copolymers allows the fabrication of the light emitting diodes by spin‐cast polymer film. The devices emit greenish‐blue light in wavelength region of 550–580 nm, which is easily visible in poorly lighted room. The quantum efficiencies are in the range of 0.002 to 0.01% (photons per electron) at room temperature; which are significantly higher than corresponding values for poly(3‐cyclohexylthiophene) based light emitting diodes. The charge carrier mobility in the device is found to be 5.6 × 10⁻⁴ cm²/Vs. ©2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1051–1055, 2000     

Properties of polymer light‐emitting diodes coated on surface‐treated ITO/glass substrates

We fabricated blue polymer light‐emitting diodes (PLEDs) with indium tin oxide (ITO)/PEDOT : PSS/PVK/PFO‐poss/LiF/Al structures. All of the organic film layers were prepared by the spin‐coating method on plasma and heat‐treated ITO/glass substrates. The dependences of the optical and electrical properties of the PLEDs on the plasma and heat treatment of the ITO film and the introduction of poly(N‐vinylcarbazole) (PVK) layer were investigated. The AFM measurements indicated that the surface roughness of the ITO transparent film was improved by the plasma and heat treatment. In the emission spectra, the intensity of the excimer peaks of the PFO‐poss [polyhedral oligomeric silsesquioxane‐terminated poly(9,9‐dioctylfluorene)] emission layer were decreased for the PLED device with the PVK film layer compared with the one without the PVK layer. The maximum current density, luminance and current efficiency of the PLEDs were found to be about 470 mA/cm², 486 cd/m² at an input voltage of 12 V and 0.55 cd/A at 100 cd/m² in luminance, respectively. The color coordinates (CIE chart) of the blue PLEDs were in the range of x = 0.17 ～ 0.20, y = 0.13 ～ 0.16, and the peak emission spectrum was about 430 nm, showing a good blue color. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Performance of white light emitting diodes prepared by casting wavelength‐converting polymer on InGaN devices

UV‐curable siloxane oligomers prepared by a hydrosilylation reaction were used as encapsulant. Two fluorescent copolymers with emission covering the range of green and red light were synthesized and blended with the UV‐curable siloxane oligomers and photoinitiator to make the wavelength‐converting polymer (WCP). WCP was casted on blue light emitting InGaN diodes and UV cured to fabricate white light emitting diodes (WLEDs). Effects of monomer compositions on the fluidity of uncured oligomer, together with the optical, thermal, and mechanical properties of the cured polysiloxane were studied. We also investigated the influence of red fluorescent polymer which was comprised of repeating units of dioctylfluorene, bisthienyl‐benzothiadiazole, and benzothiadiazole segments on the color rendering index, correlated color temperature, and luminous efficacy of WLED. Because of the good match between the absorption and emission features of the segments in the fluorescent copolymers, white LEDs can be produced by fluorescent copolymer blends which can support incomplete energy transfer. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45210.     

Synthesis and light‐emitting properties of new poly(p‐phenylenevinylene) derivatives containing oxadiazole moiety

Two new poly(p‐phenylenevinylene) (PPV) derivatives containing oxadiazole moiety (OXA‐PPV1 and OXA‐PPV2) were synthesized by the Wittig condensation polymerization reaction. Their thermal and light‐emitting properties were investigated. The single‐ and triple‐layer electroluminescent (EL) devices with configurations of ITO/polymer/Al and ITO/polymer/OXD‐7/Alq₃/Al were fabricated. They exhibited blue emission at 470 nm for OXA‐PPV1 and green emission at 560 nm for OXA‐PPV2. The turn‐on voltages of triple‐layer device were 11 V for OXA‐PPV1 and 8 V for OXA‐PPV2. The triple‐layer EL devices showed much better performance than did the single‐layer devices. The spectra indicated energy transfer occurred from segments of side chain to polymer backbone. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 422–428, 2002     

Preparation and performance of high refractive index silicone resin‐type materials for the packaging of light‐emitting diodes

A novel high refractive index and highly transparent silicone resin‐type material for the packaging of high‐power light‐emitting diodes (LEDs) is introduced, which was synthesized by hydrosilylation of vinyl end‐capped methylphenyl silicone resin and methylphenyl hydrosilicone oil catalyzed by Karstedt's catalyst. The vinyl end‐capped methylphenyl silicone resins were prepared by hydrolysis?polycondensation method from methylphenyl diethoxysilane (MePhSi(OEt)₂), phenyl triethoxysilane (PhSi(OEt)₃), and vinyl dimethylethoxy silane (Me₂ViSiOEt) in toluene/water mixture catalyzed by cation‐exchange resin. The vinyl end‐capped methylphenyl silicone resins were characterized by ¹H‐NMR and Fourier‐transform infrared. The performances of the cured silicone resin‐type materials for LED packaging have been examined in detail. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Hyperbranched polymer for light‐emitting applications

A light‐emitting partially conjugated hyperbranched polymer (2,5‐dimethoxy‐substituted hyperbranched poly(p‐phenylene vinylene), MOHPV) based on rigid fluorescent conjugated segments, 2,5‐dimethoxy‐substituted distyrylbenzene (a derivative of oligo‐poly(p‐phenylene vinylene)), and flexible non‐conjugated spacers, trioxymethylpropane, was synthesized via an A₂ + B₃ approach. The weight‐average molecular weight was 2.48 × 10⁴ g mol^?1. The introduction of two methoxy groups into central rings of the oligo‐poly(p‐phenylene vinylene) imparted to MOHPV better solubility in common organic solvents and processability than its analogues reported in our previous work, especially the fully conjugated hyperbranched polymers. The effect of the molar ratio of monomer A₂ to monomer B₃ on the molecular weight and molecular weight distribution was investigated. A single‐layer light‐emitting diode was fabricated employing MOHPV as an emitter. A double‐layer light‐emitting diode was also fabricated by doping an electron transport material, 2‐(4‐biphenylyl)‐5‐phenyl‐1,3,4‐oxadiazole, into the emitting layer and inserting a thin layer of tri(8‐hydroxyquinoline)aluminium as electron‐transporting/hole‐blocking layer. A maximum luminance of 1500 cd m^?2 at 12 V and a maximum electroluminescence efficiency of 1.38 cd A^?1 at 14 mA cm^?3, which are approximately 43.5 and 12.9 times greater, respectively, than those of the single‐layer device, were achieved. The synthetic simplicity, excellent solubility and solution processability, and less of a propensity to aggregation make MOHPV a novel type of emitter for polymer light‐emitting displays. Copyright © 2010 Society of Chemical Industry     

Improving the image of an organic light‐emitting diode using a dye‐polariser

The present work investigated the image improvement of an organic light‐emitting diode (OLED) by using a dye‐polariser on the panel of an OLED. There are many key vision indexes that can be used to indicate the image performances of flat panel displays (FPDs), such as pixel solution, brightness, view angle, visual reflective sensitivity, contrast ratio, colour saturation and response time. In this study, a dye‐polariser was applied on the panel of an OLED and experiments were conducted to examine the image performances using some relative key vision indexes. The results clearly show the effectiveness of the dye‐polariser used. The OLED showed a reduction in visual reflective sensitivity by 86.6%, improved the contrast ratio of the image to 2.4 and 2.7 times in an indoor (or office) ambience (490 cd/m²) and an outdoor ambience (1375 cd/m²), respectively, increased colour saturation from 59.4% to 66.7%, and reinforced the weaknesses of the red and blue organic fluorescent materials. © 2011 Canadian Society for Chemical Engineering     

Pyrrole‐based narrow‐band‐gap copolymers for red light‐emitting diodes and bulk heterojunction photovoltaic cells

A series of narrow‐band‐gap conjugated copolymers (PFO‐DPT) derived from pyrrole, benzothiadiazole, and 9,9‐dioctylfluorene (DOF) is prepared by the palladium‐catalyzed Suzuki coupling reaction with the molar feed ratio of 4,7‐bis(N‐methylpyrrol‐2‐yl)‐2,1,3‐benzothiadiazole (DPT) around 1, 5, 15, 30, and 50%. The obtained polymers are readily soluble in common organic solvents. The solutions and the thin solid films of the copolymers absorb light from 300 nm to 600 nm with two absorbance peaks at around 380 nm and 505 nm. The PL emission consists mainly of DPT unit emission at around 624–686 nm depending on the DPT content in solid film. The EL emission peaks are red‐shifted from 630 nm for PFO‐DPT1 to 660 nm for PFO‐DPT50. Bulk heterojunction photovoltaic cells fabricated from composite films of copolymer and [6,6]‐phenyl C₆₁ butyric acid methyl ester (PCBM) as electron donor and electron acceptor, respectively, in device configuration: ITO/PEDOT : PSS/PFO‐DPT : PCBM/Ba/Al shows power conversion efficiencies 0.15% with open‐circuit voltage (V_oc) of 0.60 V and short‐circuit current density (J_sc) of 0.73 mA/cm² under AM1.5 solar simulator (100 mW/cm²). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Fast response single‐ion transport light‐emitting electrochemical cell based on PPV derivative

We present the electrical and optical characteristics of a single‐ion transport light‐emitting electrochemical cell (SLEC) based on poly(p‐phenylene vinylene) (PPV) derivative containing aryl‐substituted oxadiazole in the backbone (MEH‐OPPV). Ionized polyurethane–poly(ethylene glycol) (PUI) used as polymer electrolyte is introduced into the active layer of the SLEC. The turn‐on voltage of the SLEC is about 3 V according to its current density–voltage (J–V) characteristics. The response time of the SLEC is less than 10 ms, lower than that of normal LECs by two orders of magnitudes roughly. The reasons of the quick response for the SLEC are discussed in the article. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4253–4255, 2006     

Synthesis and characterization of novel soluble alternating copoly(phenylene vinylene) derivative for light‐emitting electrochemical cell

A novel alternating copolymer, poly{[2,5‐di(2‐(2‐ethoxy ethoxy)ethoxy)‐1,4‐phenylene vinylene]‐alt‐1,4‐[phenylene vinylene]}, has been synthesized through the Wittig condensation as electroluminescent material. In this copolymer, one component is phenylene vinylene with flexible oligo(ethylene oxide) side chain that facilitates ion transportation and phase miscibility between nonpolar and polar part of composite luminescent layer, and another is a rigid phenylene vinylene moiety to improve luminescent quantum efficiency and tune color. The copolymer shows good solubility and thermal stability for device fabrication compared to poly(phpeylene vinylene)(PPV). The band gap value of copolymer is between those of corresponding homopolymers, which indicates that alternating copolymerization is a suitable way to obtain luminescent polymer with desired band gap. The maximum wavelength of photoluminescence of copolymer is 539 nm (yellowish‐green). The HOMO and LUMO energy levels obtained by cyclic voltammetry measurement indicate that the electron injection ability of copolymer has been greatly improved compared with that of the PPV. A more balanced carrier injection and higher quantum efficiency are proved by electroluminescent properties of corresponding light‐emitting devices. The turn‐on voltage of LEC device (ITO/copolymer + PEO + LiClO₄/Al) is found to be 2.3 V, with current comparative to LED (ITO/copolymer/Al) at 9.5 V. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1350–1356, 2003     

Synthesis and properties of partially conjugated hyperbranched light‐emitting polymers

Via A₂ + B₄ and A₂ + B₃ [where A₂ is 1,4‐distyrylol‐2,5‐butoxybenzene, B₃ is 1,1,1‐tris‐(p‐tosyloxymethyl)‐propane, and B₄ is pentaerythritol tetra(methyl benzene sulfonate)] approaches, we synthesized two kinds of partially conjugated hyperbranched polymers, hyperbranched polymer with 3 arms (HP1) and hyperbranched polymer with 4 arms (HP2), which had rigid conjugated segments [oligo‐poly(phenylene vinylene)] and flexible, nonconjugated spacers arranged alternately through ether bonds in the skeleton. The conjugated segments were modified by pendant butoxy groups, which imparted the resulting polymers with excellent solubility in common organic solvents and excellent film‐forming abilities. Fourier transform infrared and nuclear magnetic resonance spectroscopy were used to identify the structure of the monomers and polymers. Thermal property investigations showed that two polymers both had good thermal stability with their decomposition temperatures in the range 396–405°C and high glass‐transition temperatures, which are of benefit to the fabrication of high‐performance light‐emitting devices. The photophysical properties were studied, and the relative photoluminescence quantum efficiencies of HP1 and HP2 in dilute chloroform solution amounted to 56.8 and 49.3%, respectively. A brief light‐emitting diode device with a configuration of indium tin oxide/HP1/Ca/Al was fabricated, and its electroluminescence performance was studied. The brightness of the device reached an optimistic maximum of 190 cd/m² at 8.2 V. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Excimer and electromer suppression of tetraphenylsilane‐based blue‐light‐emitting polymers

Excimer and electromer suppression of tetraphenylsilane‐derivative‐based blue polymer light‐emitting devices (PLEDs) was investigated. Tetraphenylsilane with a rigid bulky structure certainly but not completely suppressed excimer formation among polymer‐chain segments. A poor solvent, toluene, resulted in excimer formation in the solid film during the spin‐coating process, which could not be suppressed by the incorporation of a bulky moiety onto the polymer backbone. In addition, electromers or electroplexes formed by the strong interaction between the oxadiazole and diphenyl(4‐tolyl)amine groups could not be prevented by the tetraphenylsilane moiety. The influences of the bulky moiety, bipolar unit, and device fabrication conditions on the suppression of excimers or electromers in PLEDs are discussed in detail. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Novel blue‐light‐emitting polymers based on a diphenylanthracene moiety

New luminescent copolyethers with diphenylanthracene‐emitting segments and electron‐transporting benzoxazole phenyl were successfully synthesized by aromatic nucleophilic substitution. The polymers, characterized by NMR and IR spectroscopy, were obtained in high yields, showed good solubility in various organic solvents, and had high thermal stability with high glass‐transition temperatures (125–129). The number‐average molecular weights of the polymers were 10,000–20,000, and they had polydispersity indices of 1.2–1.4. The optical and electrochemical properties of the polymers were also investigated. The pure blue emission for the polymers (maximum wavelength = 430–440 nm) was obtained with high photoluminescence quantum efficiency (76–78%) in a chloroform solution. The blue electroluminescence for the poly(TDPB) (maximum wavelength = 440 nm) was obtained with a turn‐on voltage of 15–20 V when simple light‐emitting diodes (indium tin oxide/polymer/Al) were fabricated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2151–2157, 2006     

Artwork imaging from 370 to 1630 nm using a novel multispectral system based on light‐emitting diodes

The recent use of multispectral systems as a noncontact method for analysis of artworks has already shown promising results. This study explains the application of a novel portable multispectral system based on light‐emitting diodes (LEDs) for artwork imaging. This method provides spectral information in a spectral range from 370 to 1630 nm with a 25 cm × 25 cm field of view by using two different image sensors in synchrony with 23 bands of irradiation. The spectral information for each point is estimated and validated using the pseudo‐inverse and spline interpolation methods for spectral estimation and three different evaluation metrics. The results of the metrics obtained with both estimation methods show a general good performance of the system over the whole spectral range. The experiments also showed that the selection of the training set for the pseudo‐inverse estimation has a great influence in its performance, and thus, it defines whether or not the pseudo‐inverse outperforms the spline interpolation method. The system is applied in situ to the study of Catalan art masterpieces, and the results demonstrate the potential of a cost‐effective and versatile system using various off‐the‐shelf elements to reconstruct color information and to reveal features not previously identified. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 398–407, 2015