Light-emitting diodes based on phosphorescent guest/polymeric host systems

Vaeth, Kathleen M.; Tang, Ching Wan

doi:10.1063/1.1501748

Cited by 145 publications

(93 citation statements)

References 9 publications

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“…We have successfully used this approach in our lab for several inorganic precursors (Al 2 O 3 , SiC, [15] SiO 2 ), organic polymers (polystyrene), and biopolymers (starch acetate). [15] For brevity two model systems are discussed here: poly(L-lactide) (PLA) and ZrO 2 .…”

Section: Methodsmentioning

confidence: 98%

“…Vaeth and Tang [15] reported an EQE of 8.5 % and a PCE of 9.9 lm W ±1 at a current density of 0.5 mA cm ±2 in a three-layer device comprising a PVK:PBD:Ir(ppy) 3 emission layer, exciton-and hole-blocking layers, and an electron injection layer. However, combining low molecular weight materials and polymers in heterostructures compromises the unique merit of PLEDs, i.e., processing only from solutions.…”

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confidence: 99%

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Highly Efficient Single‐Layer Polymer Electrophosphorescent Devices

Neher²,

et al. 2004

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Intense research is currently directed towards polymer light-emitting diodes (PLEDs) because of their potential for application in flat-panel displays. [1,2] Based on their compatibility with solution processing, the exploration of their suitability for organic electronic devices has primarily been motivated by the need for low-cost production over large areas by utilizing spin-coating, ink-jet printing, or screenprinting technologies. According to simple statistics, the process of charge injection and recombination in PLEDs generates singlet excitons with a quantum efficiency of only 25 %, setting an upper limit to the efficiency of PLEDs based on fluorescent polymers. Even though the singlet±triplet ratio in PLEDs is still a topic of debate, [3±6] it is expected that the radiative decay of both singlet and triplet states would substantially increase the efficiency of PLEDs. Phosphorescent dyes have been used to overcome the efficiency limit imposed by the unavoidable formation of triplet excitons, and highly efficient phosphorescent light-emitting diodes based on low molecular weight materials have been demonstrated.[7±9]These high-efficiency devices typically consist of several layers including a hole-transporting layer, an emission layer doped with the phosphorescent dye, an exciton-/hole-blocking layer and an electron-injecting layer. In fact, a multilayer LED utilizing fac-tris(2-phenylpyridine)iridium (Ir(ppy) 3 ) as the emitting species exhibited a very high external quantum efficiency (EQE) of 19.2 % and a power conversion efficiency (PCE) of 72 lm W ±1 at 65 cd m ±2 .[9]Polymer phosphorescent light-emitting diodes (PPLEDs) usually utilize a phosphorescent dye doped into a chargetransporting polymer matrix.[10±17] One of the criteria for the selection of the polymer matrix is that the energy of the lowest lying triplet state (T 1 ) of the host is larger or at least comparable to that of the phosphorescent guest. In case of Ir(ppy) 3 with a triplet energy of about 2.4 eV, mostly non-conjugated polymers, such as poly(N-vinyl-carbazole) (PVK), have been used. [11±16] In order to optimize the balance of charge-carrier injection and transport and to confine the emissive triplet excitons within the emission layer, the structure of PPLEDs generally resembles that of low molecular weight material multilayer devices.[11±15] Yang and Tsutsui were the first to publish an efficient multilayer PPLED with a PVK:Ir(ppy) 3 emission layer and an evaporated low molecular weight electron-transporting layer.[11] These devices exhibited an external quantum efficiency of up to 7.5 %. A luminance of 100 cd m ±2 was reached at about 14 V and the power conversion efficiency was 5.8 lm W ±1 under these conditions.Lamansky et al. [14] achieved EQEs of 3.4 % in single-layer structures by adding the low molecular weight electron-transporting molecule 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) to the PVK host to facilitate electron transport. Vaeth and Tang [15] reported an EQE of 8.5 % and a PCE of 9.9 lm W ±1 ...

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Section: Methodsmentioning

confidence: 98%

mentioning

confidence: 99%

Highly Efficient Single‐Layer Polymer Electrophosphorescent Devices

Neher²,

et al. 2004

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“…Adding an extra hole-blocking layer, Vaeth et al [14] recently reported a high of 8.5% in a relatively more complex triple-layer device.…”

Section: Introductionmentioning

confidence: 99%

“…Phosphorescent emission dopants have also been applied to polymer-based OLEDs [5]- [14]. Using a single 100-200-nm-thick tris[9,9-dihexyl-2-(pyridinyl-) fluorene] iridium(III) doped blend of hole-transporting poly(9-vinylcarbazole) (PVK) and electron-transporting 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole, Gong et al [12] the turn-on voltage was relatively high, resulting in a low of 2.5 lm/W.…”

Section: Introductionmentioning

confidence: 99%

Polymer Electrophosphorescent Light-Emitting Diode Using Aluminum Bis(2-Methyl-8-Quinolinato) 4-Phenylphenolate as an Electron-Transport Layer

Qiu

Xie

Chen

et al. 2004

IEEE J. Select. Topics Quantum Electron.

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Abstract-The characteristics of organic light-emitting diodes depend critically on the arrangement and choice of the constituent organic layers. Diodes constructed using poly(vinylcarbazole) doped with phosphorescent fac tris(2-phenylpyridine) iridium (III) [Ir(ppy) 3 ] as the polymer hole-transport layers and aluminum (III) bis(2-methyl-8-quinolinato) 4-phenylphenolate as hole-blocking and electron-transport layers were investigated. The peak efficiencies of the diodes were sensitive to the concentration of Ir(ppy) 3 . With an optimal 2 wt% concentration, an effective external quantum efficiency of 10% photons/electron, a luminance power efficiency of 7.3 lm/W, and a low turn-on voltage of 6 V were obtained.

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“…10 Therefore, better matching between the host material and deep blue dopant material with sufficient spectral overlap for Förster energy transfer 11 is required for deep blue emission with high efficiency. [12][13][14][15][16][17][18][19][20] Also, an OLED's quantum efficiency is determined by the carrier injection and recombination in the emitting layer (EML); therefore, the balance between electrons and holes in the EML is the most important factor to obtain higher quantum efficiency. This study contributes to the understanding of significant effects of double EMLs and host-dopant systems of blue OLEDs with 4,4'-bis (9-ethyl-3-carbazovinylene)-1,1'biphenyl (BCzVBi) doped to two different host materials of 4,4-bis (2,2-diphenylyinyl)-1,10-biphenyl (DPVBi) and 9,10-bis (2-naphthyl) anthracene (ADN).…”

Section: Introductionmentioning

confidence: 99%

Highly efficient blue organic light-emitting diodes using dual emissive layers with host-dopant system

Lee

Kim

et al. 2013

J. Photon. Energy

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Abstract. We fabricated highly efficient blue organic light-emitting diodes (OLEDs) by designing differing emitting layer structures with fluorescent host and dopant materials of 4,4-bis (2,2-diphenylyinyl)-1,10-biphenyl and 9,10-bis (2-naphthyl) anthracene as host materials and 4,4'-bis (9-ethyl-3-carbazovinylene)-1,1'biphenyl (BCzVBi) as a dopant material to demonstrate electrical and optical improvements. Best enhancement in luminance and luminous efficiency were achieved by a quantum well structure in device F with 8668 cd∕m 2 at 8 V and 5.16 cd∕A at 103.20 mA∕cm 2 , respectively. Among the blue OLED devices doped by BCzVBi, device B emits the deepest blue emission with Commission Internationale de l'É clairage coordinates of (0.157, 0.117) at 8 V. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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Light-emitting diodes based on phosphorescent guest/polymeric host systems

Cited by 145 publications

References 9 publications

Highly Efficient Single‐Layer Polymer Electrophosphorescent Devices

Highly Efficient Single‐Layer Polymer Electrophosphorescent Devices

Polymer Electrophosphorescent Light-Emitting Diode Using Aluminum Bis(2-Methyl-8-Quinolinato) 4-Phenylphenolate as an Electron-Transport Layer

Highly efficient blue organic light-emitting diodes using dual emissive layers with host-dopant system

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