White Polymer Light-emitting Diodes Research Articles

Highly Efficient White Polymer Light‐Emitting Diodes Based on Nanometer‐Scale Control of the Electron Injection Layer Morphology through Solvent Processing

Highly efficient white polymer light-emitting diodes (WPLEDs) are demonstrated using neutral conjugated polymer surfactant PFN-OH as the electron-injection layer through solution processing. The electroluminescence spectra and luminance efficiency are strongly dependent on the morphology of the PFN-OH films. The dramatic improvement of device performance is attributed to the efficient hole-blocking ability due to mixed solvent-induced PFN-OH chain aggregation.

Broad band and white phosphorescent polymer light-emitting diodes in multilayer structure

Efficient phosphorescent polymer light-emitting diode with poly(vinylcarbazole) (PVK) doped by two or three iridium complexes in single and bilayer structures are studied. With (tris-(2-4(4-toltyl) phenylpyridine) (Ir(mppy) 3) as the green emitter and (1-phenylisoquinoline) (acetylacetonate) iridium(III) (Ir(piq) 2) as the red emitter the efficiency is as high as 23 cd/A with broad band emission from 500 nm to 720 nm. For white emission a second layer is added with blue emitter ((III) bis[(4,-6-di-fluorophenyl-pyridinato)N,C 2] picolinate) (FIrpic) doped in PVK. White light containing three spectral peaks results with efficiency 8.1 cd/A. As the second blue layer is replaced by the fluorescent (poly(9,9-dioctylfluorene)) (PFO) white emission with high color rendering index 86 is achieved. The efficiency is 5.7 cd/A with peak luminance 8900 cd/m 2. For a given iridium complexes ratio the relative intensity of the green and red emission depends sensitively on the second blue layer.

High-efficiency and solution processible multilayer white polymer light-emitting diodes using neutral conjugated surfactant as an electron injection layer

High-efficiency white polymer light-emitting diodes were fabricated by using an yellow-emitting osmium complex Os(fptz)2(dppe) [fptz=3-trifluoromethyl-5-(2-pyridyl)-1,2,4-triazole, dppe=cis-1,2-bis-(dipheneyl-phosphino) ethylene] doped into blue fluorescent copolymer based on an ultraviolet-blue light emitting host poly[2,7-(9,9-dioctylfluorene)-co-1,3-(5-carbazolphenylene)] and a blue light emitting component 4-N,N-diphenylaminostilbene (PFCz-DPS1-OXD5) as the emissive layer and a neutral conjugated surfactant, poly[9,9-bis(6′(diethanolamino)hexyl)-fluorene] (PFN-OH), as the electron injection layer sandwiched between the emissive layer and Al cathode. The device with the configuration of indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid)/poly(N-vinylcarbazole)/Os(fptz)2(dppe)(1wt%):PFCz-DPS1-OXD5∕PFN-OH∕Al exhibited efficient white light emission at the Commission Internationale de I’Eclairage coordinates of (0.33, 0.34) and a maximum luminance efficiency of 16.9cd∕A and brightness of 22100cd∕m2.

Efficient Single Active Layer Electrophosphorescent White Polymer Light‐Emitting Diodes

Efficient electrophosphorescent white emission polymer light-emitting diodes (PLEDs) with single active layer is reported. Despite their simple architectures and straightforward fabrication procedures, double-doped devices with CIE coordinate of (0.33, 0.36) at 12 mA cm–2 can show peak PE of 6.4 lm W–1 and a peak LE of 16.1 cd A–1 for forward viewing, while triple-doped device (0.34, 0.47) can show a peak PE of 10.0 lm W–1 and a peak LE of 24.3 cd A–1. The demonstrated efficient white PLEDs hold great promise for solid state lighting application.

Efficient multilayer white polymer light-emitting diodes with aluminum cathodes

Efficient multilayer white polymer light-emitting diodes (WPLEDs) with aluminum cathodes are fabricated. The multilayer structure is composed of a water soluble hole-injection layer, a toluene-soluble emissive layer, and an alcohol-soluble emissive layer. The polarity difference of the solvents used for spin coating these polymers allows for realization of the multilayer polymer structure. The recombination zone confined at the interface of the two emissive polymers avoids exciton quenching by electrodes, and white emission is realized by harvesting photons emitted from the two emissive polymers. A maximum luminous efficiency of 16.9cd∕A and a power efficiency of 11.1lm∕W are achieved for this WPLED.

White polymer light-emitting diodes based on poly(2-(4′-(diphenylamino)phenylenevinyl)-1,4-phenylene- alt-9,9- n-dihexylfluorene-2,7-diyl) doped with a poly( p-phenylene vinylene) derivative

Efficient white polymer light-emitting diodes based on the polymer blend of poly(2-(4′-(diphenylamino)phenylenevinyl)-1,4-phenylene- alt-9,9- n-dihexylfluorene-2,7-diyl) doped with poly{2-[3′,5′-bis(2ʺ-ethylhexyloxy) benzyloxy]-1,4-phenylenevinylene}- co-poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) were fabricated. The electroluminescence (EL) spectrum is easily controlled by changing the dopant concentration. A white light emission was realized on the device with the dopant concentration of 0.194‰ and the emission light is less sensitive to the applied voltage in a wide voltage range. The maximum luminance and the maximum EL efficiency of the single-layer device were 2330 cd/m 2 and 0.29 cd/A, respectively. By introducing an Alq 3 layer as an electron transporting and hole blocking layer, the overall performance of the double layer device was dramatically improved, the maximum luminance and the maximum EL efficiency reached 3300 cd/m 2 and 2.37 cd/A, respectively.

Double-Layer Structured WPLEDs Based on Three Primary RGB Luminescent Polymers: Toward High Luminous Efficiency, Color Purity, and Stability

Efficient white polymer light-emitting diodes (WPLEDs) were fabricated on the basis of three kinds of luminescent polymers: poly{2-[3‘,5‘-bis(2‘ ‘-ethylhexyloxy)benzyloxy]-1,4 phenylenevinylene}-co-poly(2-methoxy-5-(2‘-ethyl-hexy loxy)-1,4-phenylene vinylene) (BE-co-MEH-PPV), red; poly(6,6‘-bi-(9,9‘-dihexylfluorene)-co-(9,9‘-dihexylfluorene-3-thiophene-5‘-yl)) (PFT), green; and poly(9,9-dioctylfluorene-2,7-diyl) (PFO), blue. In order to overcome the complicated cascade energy transfer and deep trapping process, the two narrow band gap red and green light-emitting polymers are separated into two layers. In the bottom emission layer, hole-transporting material poly(N,N‘-bis(4-butylphenyl)-N,N‘-bis(phenyl)benzidine (poly-TPD) and electron-blocking material poly(N-vinylcarbazole) (PVK) were chosen to work together as binary-host; concomitantly, the novel red light-emitting polymer BE-co-MEH-PPV was employed as guest. In addition, in order to avoid phase separation in the top emission layer, two fluorene-deri...

White‐Light Emission from a Single Polymer with Singlet and Triplet Chromophores on the Backbone

AbstractSummary: A strategy to generate an efficient white‐light emission has been developed by mixing fluorescence and phosphorescence emission from a single polymer. Fluorene is used as the blue‐emissive component, benzothiadiazole (BT) and the iridium complex [(btp)2Ir(tmd)] are incorporated into a polyfluorene backbone, respectively, as green‐ and red‐emissive chromophores by Suzuki polycondensation. By changing the contents of BT and [(btp)2Ir(tmd)] in the polymer, the electroluminescence spectrum from a single polymer can be adjusted to achieve white‐light emission. A white polymeric light‐emitting diode (WPLED) with a structure of ITO/PEDOT:PSS/PVK/PFIrR1G03/CsF/Al shows a maximum external quantum efficiency of 3.7% and the maximum luminous efficiency of 3.9 cd · A−1 at the current density of 1.6 mA · cm−2 with the CIE coordinates of (0.33, 0.34). The maximum luminance of 4 180 cd · m−2 is achieved at the current density of 268 mA · cm−2 with the CIE coordinates of (0.31, 0.32). The white‐light emissions from such polymers are stable in the white‐light region at all applied voltages, and the electroluminescence efficiencies decline slightly with the increasing current density, thus indicating that the approach of incorporating singlet and triplet species into the polymer backbone is promising for WPLEDs.Structure of PFIrR1G04 and the EL spectra of its devices under various voltages. Device structure: ITO/PEDOT:PSS/PVK/polymer/CsF/Al.magnified imageStructure of PFIrR1G04 and the EL spectra of its devices under various voltages. Device structure: ITO/PEDOT:PSS/PVK/polymer/CsF/Al.

White polymeric light-emitting diodes with high color rendering index

The efficient white polymeric light-emitting diodes based on a white emissive polymer doped with a red phosphorescent dopant were fabricated by spin-coating method. The emission spectrum of the device is broadened to cover the full visible region by doping the red phosphorescent dye and thereby realizes white emission with high color-rendering index (CRI). By controlling the contents of the doped electron-transporting 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole and the red phosphorescent dopant, a luminous efficiency as high as 5.3cd∕A and a power efficiency of 3lm∕W were obtained with a CRI of 92.

High-Efficiency White Polymer Light-Emitting Diodes Based on Blended RGB Polymers

We have fabricated white polymer light-emitting devices (WPLEDs) from RGB polymer blending systems using ITO/PEDOT:PSS/blended polymers/LiF/Al structure. The highest current efficiency reached 5.34 cd/A and the maximum brightness value of 27,000 cd/m2 at 11.4 V was obtained. As the green dopant concentration increased, the spectrum deviated from the white because of more energy transfer from host to guest. As a result, the 450 nm blue peak was reduced by increasing green dopant ratio. On the other hand, 600 nm red shoulder peaks were slightly increased at the same conditions. Therefore, red-orange and green electroluminescence emissions are promoted by excitation energy and charge transfer from the blue host polymer to the dopants.

Enhanced performance of white polymer light-emitting diodes using polymer blends as hole-transporting layers

AU: PLEASE CONFIRM CHANGES MADE IN THE BYLINE.White polymer light-emitting diodes (WPLEDs) with the Commission Internationale de l’Enclairage coordinates of (0.32, 0.34) are demonstrated with poly(9,9-dioctylfluorene-2,7-diyl) as host and poly(5-methoxy-2-(2′-ethyl-hexylthio)-p-phenylenevinylene) as guest. Blends of poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (poly-TPD) and poly(N-vinyl-carbazole) (PVK) are introduced into bilayer devices as hole-transporting layers (HTLs). Because the blends combined the hole-injection and hole-transporting capabilities of poly-TPD with electron-blocking capability of PVK, WPLEDs with the blends as HTLs exhibit enhanced performance in comparison with single-layer device and bilayer devices with pure poly-TPD or pure PVK as HTL. With a 1:1 weight ratio of poly-TPD to PVK in the blend, the WPLED achieves a maximum brightness of ∼5000cd∕m2 with a maximum electroluminescent efficiency of 3.15cd∕A.

Improving the power efficiency of white light-emitting diode by doping electron transport material

Highly efficient white light emission was realized via the partial energy transfer from blue host polyfluorene (PF) to orange light emission dopant rubrene. A more balanced charge transport was achieved by adding an electron transport material, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), into the PF-rubrene system to enhance the electron transportation. Efficiency improvement by as much as a factor of 2 has been observed through the addition of PBD. These devices can easily reach high luminance at low driving voltages, thus achieving high power efficiency at high luminance (14.8, 13.5, and 12.0lm∕W at the luminances of 1000, 2000, and 4000cd∕m2, respectively). Therefore, this performance is an important approach toward solid-state lighting application. The enhancement is mainly attributed to three factors: increased electron transport property of the host material, increased photoluminescence quantum efficiency, and the shifting of emission zone away from cathode contact. The reported efficiency is among the highest values reported in the white emission polymer light-emitting diodes.

White light from polymer light-emitting diodes: Utilization of fluorenone defects and exciplex

A white light polymer light-emitting diode was demonstrated with a double layer configuration: poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (poly-TPD) blended with poly(N-vinylcarbazole) as both hole-transporting layer and electron-blocking layer, blue-emissive poly(9,9-dihexylfluorene-alt-co-2,5-dioctyloxy-para-phenylene) (PDHFDOOP) blended with green-emissive poly[6,6′-bi-(9,9′-dihexylfluorene)-co-(9,9′-dihexylfluorene-3-thiophene-5′-yl)] as an emissive layer. By annealing the emissive layer at a relatively high temperature, fluorenone defects were generated into PDHFDOOP, which formed an exciplex with poly-TPD, as a red emitter. The devices exhibit a maximum brightness of ∼4800cd∕m2 and a maximum luminous efficiency of ∼3cd∕A. Moreover, the Commission Internationale de L’Eclairage coordinates of the emitted light is close to that of pure white light and is insensitive to the applied voltages.

White polymeric light-emitting diode based on a fluorene polymer∕Ir complex blend system

Efficient white-polymeric light-emitting diodes (PLED) were fabricated as a single active layer containing blue-emitting poly(9,9-bis(2-ethylhexyl)fluorene-2,7-diyl) endcapped with bis(4-methylphenyl)phenylamine; (PF2∕6am4), and yellow-orange-emitting iridium [tri-fluorenyl] pyridine complex [Ir(Fl3Py)3]. The fluorene-like ligands in the blended device prevent phase segregation and also enhance energy transfer from the polymer host to the guest due to efficient overlap of wave function (Dexter process) and host singlet emission and guest absorption bands (Förster process) which reduces the loading level required to produce white emission. The two emitted colors complement each other and doping levels of 2%–3% produce white emission. Above a certain current density, depending on the doping level, the device Commission Internationale de L’Eclairage (CIE) coordinates become bias independent and a stabilized white emission can be obtained. A white-emitting PLED (coordinates 0.348, 0.367) of peak external quantum efficiency of 2.8%, and luminance of 16000cd∕m2 at applied voltage of 5V (i.e., 4.57cd∕A) was obtained.

White polymer light-emitting devices from ternary-polymer blend with concentration gradient

We have fabricated a white polymer light-emitting-diode bilayer structure that contains a ternary polymer blend. The first layer of poly(9-vinylcarbazole) acts as an energy donor and electron blocker, and the second layer comprising an immiscible polymer blend of two light-emitting polymers, poly(9,9′-dihexylfluorene-2,7-divinylene- m-phenylenevinylene- stat- p-phenylenevinylene) and poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene), emits light. The emissive white color of the device was observed to be practically independent of the driving voltage (near CIE coordinate; 0.33, 0.33). In addition, it shows greatly enhanced luminous efficiency compared to a ternary blended white light-emitting-diode.

Efficient single-layer “twistacene”-doped polymer white light-emitting diodes

Bright, efficient, and stable white polymer light-emitting diodes based on blue polyfluorene doped by a “twistacene,” 6, 8, 15, 17-tetraphenyl-1.18, 4.5, 9.10, 13.14-tetrabenzoheptacene (3) (TBH), are demonstrated. In “twistacene” the terminal pyrene moieties serve two functions: (i) to stabilize the inherently unstable heptacene and (ii) to enable the oligoacene to be a strongly fluorescent molecule. As a result, efficient and very bright white polymer light-emitting diodes are obtained. The maximum luminance of the devices exceeds 20000cd∕m2. The maximum luminous efficiency is 3.55cd∕A at 4228cd∕m2 while the maximum power efficiency is 1.6lm∕W at 310cd∕m2. The device obtains a stable white balance by a combination of energy transfer from the blue polyfluorene to TBH by 1% TBH doping plus the host emission. The device emission color is not a function of bias current, which is ideal for various applications, from lighting to the backlight for liquid crystal displays.

White electroluminescence from polyfluorene chemically doped with 1,8-napthalimide moieties

An efficient white light-emitting polymer was developed with blue polyfluorene (PFO) chemically doped with orange fluorescent 1, 8-naphthalimide moieties. The emission spectrum can be easily tuned by varying the content of 1, 8-naphthalimide moieties. A white polymeric light-emitting diode (WPLED) with a structure of indium tin oxide (ITO)/the complex of (3,4-ethylenedioxythiophene) and polystyrene sulfonic acid (PEDOT)/polymer∕Ca∕Al showed a current efficiency of 5.3cd∕A and a power efficiency of 2.8Lm∕W at 6V with the Commission Internationale de L'Eclairage (CIE) coordinates at (0.25,0.35). Moreover, the WPLED from the copolymer showed a very stable white light emission at different driving voltage and brightness. The CIE coordinates of the WPLED were (0.25, 0.35), (0.26, O.36), and (0.26, 0.36) under driving voltages of 6, 8, and 10V, corresponding to the brightness of 82, 3555, and 7530cd∕m2, respectively. This approach for realization of white light emission is promising over the polymer blending system in terms of both efficiency and color stability.