Electrophosphorescent Devices Research Articles

Synthesis of fluorene‐based hyperbranched polymers for solution‐processable blue, green, red, and white light‐emitting devices

AbstractFor the purpose of making hyperbranched polymer (Hb‐Ps)‐based red, green, blue, and white polymer light‐emitting diodes (PLEDs), three Hb‐Ps Hb‐terfluorene (Hb‐TF), Hb‐4,7‐bis(9,9′‐dioctylfluoren‐2‐yl)‐2,1,3‐benzothiodiazole (Hb‐BFBT), and Hb‐4,7‐bis[(9,9′‐dioctylfluoren‐2‐yl)‐thien‐2‐yl]‐2,1,3‐benzothiodiazole (Hb‐BFTBT) were synthesized via [2+2+2] polycyclotrimerization of the corresponding diacetylene‐functionalized monomers. All the synthesized polymers showed excellent thermal stability with degradation temperature higher than 355 °C and glass transition temperatures higher than 50 °C. Photoluminance (PL) and electroluminance (EL) spectra of the polymers indicate that Hb‐TF, Hb‐BFBT, and Hb‐BFTBT are blue‐green, green, and red emitting materials. Maximum brightness of the double‐layer devices of Hb‐TF, Hb‐BFBT, and Hb‐BFTBT with the device configuration of indium tin oxide/poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate)/light‐emitting polymer/CsF/Al are 48, 42, and 29 cd/m2; the maximum luminance efficiency of the devices are 0.01, 0.02, and 0.01 cd/A. By using host–guest doped system, saturated red electrophosphorescent devices with a maximum luminance efficiency of 1.61 cd/A were obtained when Hb‐TF was used as a host material doped with Os(fptz)2(PPh2Me2)2 as a guest material. A maximum luminance efficiency of 3.39 cd/A of a red polymer light‐emitting device was also reached when Hb‐BFTBT was used as the guest in the PFO (Poly(9,9‐dioctylfluorene)) host layer. In addition, a series of efficient white devices were, which show low turn‐on voltage (3.5 V) with highest luminance efficiency of 4.98 cd/A, maximum brightness of 1185 cd/m2, and the Commission Internationale de l'Eclairage (CIE) coordinates close to ideal white emission (0.33, 0.33), were prepared by using BFBT as auxiliary dopant. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Phosphonate functionalized oxadiazole derivative as an efficient electron transporting material for solution-processed blue electrophosphorescent devices

An efficient electron transporting material, P-OXD (1,3-bis[(4-(4-diethylphosphoryl-butyl-phenyl))-1,3,4-oxidiazol-2-yl]phenylene), has been synthesized and thoroughly characterized. Due to its alcohol-soluble nature, P-OXD can be spin-coated atop the light emitting layer to form high quality film without dissolving the underlying layer. As a consequence, the double-layer blue electrophosphorescent device has been successfully fabricated, giving a peak luminous efficiency of 10.5 cd/A, and a maximum brightness of 8200 cd/m² with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.16, 0.33). The promising results indicate that P-OXD has a potential application in solution-processed multilayer polymer light-emitting diodes.

Spiro‐Configured Bipolar Host Materials for Highly Efficient Electrophosphorescent Devices

In this study, we synthesized and characterized a series of spirobifluorene-based bipolar compounds (D2 ACN, DNPACN, DNTACN, and DCzACN) in which a dicyano-substituted biphenyl branch, linked orthogonally to a donor biphenyl branch bearing various diarylamines, acted as an acceptor unit allowing fine-tuning of the morphological stability, triplet energy, bipolar transport behavior, and the HOMO and LUMO energy levels. The promising physical properties of these new compounds, together with their ability to transport electrons and holes with balanced mobilities, made them suitable for use as host materials in highly efficient phosphorescent organic light-emitting diodes (PhOLEDs) with green iridium-based- or red osmium-based phosphors as the emitting layer (EML). We adopted a multilayer structure to efficiently confine holes and electrons within the EML, thus preventing exciton diffusion and improving device efficiency. The device incorporating D2 ACN doped with the red emitter [Os(bpftz)(2)(PPhMe(2))(2)] (bpftz=3-(trifluoromethyl)-5-(4-tert-butylpyridyl)-1,2,4-triazolate) gave a saturated red electrophosphorescence with CIE coordinates of (0.65, 0.35) and remarkably high efficiencies of 20.3 % (21 cd A(-1)) and 13.5 Lm W(-1) at a practical brightness of 1000 cd m(-2).

Saturated red polymer electrophosphorescent devices with meso-tetrakis (4-n-decanoyl-phenyl) porphyrin platinum (Ⅱ) complex as emitters

在聚2,7-（9,9-二辛基）芴（PFO）和30%的2-（对联苯基）-5-（对叔丁基苯基）-1,3,4-二唑（PBD）主体材料中掺杂短磷光寿命的meso-四（对正葵酰氧基苯基）卟啉铂（TDPPPt）,制成聚合物基发光器件。器件结构为：ITO/PEDOT∶PSS/PVK/PFO＋30%PBD∶TDPPPt/Ca/Al（ITO：氧化铟锡;PEDOT：聚3,4-乙撑二氧噻吩;PSS：聚苯乙烯磺酸盐;PVK：聚乙烯基咔唑）。当客体掺杂浓度≥3%时,器件给出饱和的红色发射。当驱动电压从7 V升高至14 V时,器件发光色度保持不变,CIE（国际发光照明委员会）色坐标稳定在（0.66,0.28）左右。器件的最大亮度和电流效率分别为1 390 cd/m2和1.34 cd/A。在电流密度100×10-3和150×10-3 A/cm2时,电流效率分别为1.18和0.99 cd/A,器件在高电流密度下具有良好的稳定性。

Efficient and low potential operative host/guest concentration graded bilayer polymer electrophosphorescence devices

This study investigates enhanced electrophosphorescence and its mechanism in poly(N-vinyl carbazole) (PVK): N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1-biphenyl]-4,4′-diamine (TPD)/2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD): fac-tris(2-phenylpyridine)iridium [Ir(ppy) 3] concentration graded bilayer electroluminescence devices. The two layers are partially intermixed at the bilayer interface because the upper layer (composed of Ir(ppy) 3 and PBD) was spun cast from a solvent that slightly swells the bottom layer (composed of PVK and TPD). Moreover, PBD in the upper layer can act as an efficient electron transport layer as well as a hole blocking layer, resulting in greatly enhanced electron–hole recombination. An indium tin oxide (ITO)/3,4-polyethylenedioxythiophene–polystyrenesulfonate (PEDOT)/[PVK:TPD/Ir(ppy) 3:PBD] bilayer/LiF/Al device showed dramatically decreased turn-on and driving voltages, enhanced luminescence efficiency, and narrower emission spectra compared to those of conventional ITO/PEDOT:PSS/[PVK:TPD:Ir(ppy) 3:PBD] blend/LiF/Al devices.

Highly efficient blue organic electrophosphorescence devices using a trifluorine-replaced iridium complex

Highly efficient blue phosphorescent organic light-emitting devices have been achieved by using a new emitter Iridium complex, bis[(3,4,5-trifluorophenyl)-pyridinato-N,C 2′] picolinate (F 3Irpic). For a mCP:4%F 3Irpic device, blue emission with a maximum power efficiency of 18.1 lm/W has been realized, which is much higher than those of FIrpic based devices. The emission peak was located at 480 nm with a subpeak at 511 nm. By using an optimized device structure with a better host material, performance of the device can be further increased to give a maximum power efficiency of 33.7 lm/W.

Bipolar Host Materials: A Chemical Approach for Highly Efficient Electrophosphorescent Devices

The future of organic light-emitting devices (OLEDs) is drifting from electrofluorescence toward electrophosphorescence due to the feasibility of realizing 100% internal quantum efficiency. There is limited availability of transition metals (TMs) such as Ir, Os, and Pt, which are used for color-tunable phosphorescent emitters, and the use of the host-guest strategy is necessary for suppressing the detrimental triplet-triplet annihilation inherently imparted by the TM-centered emitters. The inevitable demands of organic host materials provide organic chemists with tremendous opportunities to contribute their expertise to this technology. With suitable molecular design and judicious selection of chemical structures featured with different electronic nature, the incorporation of hole-transporting (HT) and electron-transporting (ET) moieties combines the advantages of both functional units into bipolar host materials, which perform balanced injection/transportation/recombination of charge carriers and consequentially lead the OLEDs to have higher performances and low roll-off efficiencies. This review highlights recently developed bipolar host materials with the focus on molecular design strategies and the structure-property-performance relationships of various classes of bipolar host materials, which are classified into several categories according to the structural features of their constituents (HT/ET blocks and spacers).

Color-tunable electrophosphorescent device fabricated by a photo-bleaching method

We demonstrated an efficient color-tunable electrophosphorescent device fabricated by a photo-bleaching method. Electroluminescence studies indicate that excellent device performance can be achieved through efficient Förster energy transfer from the conjugated polymer to the iridium complexes by improving their miscibility. The use of a very low concentration of red phosphorescent dye and the easy degradation characteristics of conjugated structure of the red dopant enable color-tuning from red to green emission by a simple UV-irradiation process without a sacrifice of luminescent properties.tp

A Saturated Red-Emitting Phosphorescent Iridium(III) Complex for Application in Organic Light Emitting Diodes

A novel ancillary ligand (2-(1-hydroxy-naphthyl)-benzothiozolato) (HNBT) and corresponding iridium(III) complex, Ir(ppy)2(NBT) (ppy = 2-phenylphridine) are synthesized, and red-emitting electrophosphorescent devices by doping Ir(ppy)2(NBT) in 4,4′-N,N′-dicarbazole-biphenyl (CBP) are fabricated. the optimized device displays EL spectrum with a narrow full-width at half-maximum of 65 nm, and the Comission International de L’Eclairage (CIE) coordinates of (0.65, 0.33) are very close to those suggested by the National Television System Committee (NSTC) standard for a red emitter.

Host and Dopant Materials for Idealized Deep‐Red Organic Electrophosphorescence Devices

Host and Dopant Materials for Idealized Deep‐Red Organic Electrophosphorescence Devices

High-efficiency blue-green electrophosphorescent light-emitting devices using a bis-sulfone as host in the emitting layer

A bis-sulfone small molecule, 4,4′-bis(phenylsulfonyl)biphenyl has been evaluated as a host for the phosphor iridium(III) bis(2-(4,6-difluorophenyl)pyridinato- N, C 2′)picolinate in blue-green organic light-emitting devices. In addition, a poly(norbornene)-based polymer functionalized with a 3,6-bis(carbazol-9-yl)carbazole moiety as a side group is utilized as a solution-processible hole-transport layer; comparison is made to the widely-used hole-transport polymer poly( N-vinylcarbazole) (PVK). At 100 cd/m 2, the highest efficiency device incorporating the new polymer achieved an external quantum efficiency (EQE) of 6.9% (12.9 cd/A) with a turn-on voltage of 4.3 V. In comparison, the highest efficiency device using PVK achieved an EQE of 6.4% (11.3 cd/A) with a turn-on voltage of 6.0 V.

Electrophosphorescent devices with solution processible emitter and hole transport layer stack

The light emitting behavior of the electrophosphorescent devices with solution-processible hole transport layer and light emitting layer was characterized. We have introduced the hole-transporting stacked layer composed of poly(3,4-ethylenedioxy thiophene): poly(4-styrenesulfonate) [PEDOT:PSS] and thin perfluorinated ionomer, aiming for the improvement of charge injection and transport with corresponding high efficiency behavior. In order to provide a suitable work function, composition and thickness of the ultra-thin perfluorinated ionomer was optimized for being an interfacial layer condition; 34 cd/A of green phosphorescent device was obtained while the control device without ionomer shows the luminous efficiency of 29 cd/A. Both for devices with vacuum-deposited and solution-processed electrophosphorescent emitters, change of the device efficiencies were analyzed in terms of the work function, surface chemical composition, and charge conduction behavior.

Synthesis and electrophosphorescent device study of carbazole containing dendronized styrenic polymers

Styrenic polymers P1(G0-CZ) and P2(G2-CZ) with carbazoles and carbazole containing dendrons as side chains were efficiently synthesized via “graft-to” approach by using copper-catalyzed azide/alkyne cycloaddition (CuAAC) reaction. The new polymers showed wide band gaps and had good thermal stabilities. Two new polymers were studied as electrophosphorescent host materials in OLED devices. Electrophosphorescent devices with the configuration of ITO/PEDOT:PSS/polymers:Ir(ppy) 3/TPBI/LiF/Al were fabricated. The polymer P1(G0-CZ) based device showed a maximum current efficiency of 21.4 cd/A, a power efficiency of 12.7 lm/W and an external quantum efficiency of 6.02%. The effect of host polymer structures on the aggregation of transition metal complexes Ir(ppy) 3 in active layer was also investigated.

Bipolar Heteroleptic Green Iridium Dendrimers Containing Oligocarbazole and Oxadiazole Dendrons for Bright and Efficient Nondoped Electrophosphorescent Devices

Bipolar heteroleptic green light-emitting iridium (Ir) dendrimers G(OXD) and G(DOXD) have been designed and synthesized under mild conditions in high yields, in which the first C^N and second O^O ligands are functionalized with oligocarbazole- and oxadiazole-based dendrons, respectively. To avoid affecting the optical properties of the emissive iridium core, all the functional moieties are attached to the ligands through a flexible spacer. Compared with the unipolar dendrimer G(acac), dendrimers G(OXD) and G(DOXD) exhibit the close emission maxima of 511-512 nm and photoluminescence quantum yield of 0.39-0.40 in a solution of toluene. Moreover, on going from G(acac) to G(OXD) and G(DOXD), we have found that the introduction of oxadiazole fragments decreases the lowest unoccupied molecular orbital (LUMO) energy levels to facilitate the electron injection and electron transporting, while their highest occupied molecular orbital (HOMO) energy levels remain unchanged. This means that, we can individually tune the HOMO and LUMO energy levels based on the heteroleptic structure to ensure the relative independence between the hole and electron in the emitting layer (EML), which is a favorable feature for bipolar optoelectronic materials. As a result, a bilayer nondoped electrophosphorescent device with G(DOXD) as the EML gives a maximum luminous efficiency of 25.5 cd A(-1) (η(ext): 7.4%) and a brightness of 33,880 cd m(-2). In comparison to G(acac) (17.2 cd A(-1), 17,680 cd m(-2)), both the efficiency and brightness are improved by about 1.5 and 2 times, respectively. These state-of-the-art performances indicate the potential of these bipolar heteroleptic iridium dendrimers as solution-processible emitting materials for nondoped device applications.

Enhanced efficiency in mixed host red electrophosphorescence devices

Enhanced efficiency of red phosphorescent organic light-emitting devices is observed by using a bis[2-(2′-benzothienyl)pyridinato-N,C3′] iridium(acetylacetonato) doped 4,4′-N,N′-dicarbazole-biphenyl (CBP) and 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBI) mixed host emitting layer. The CBP:TPBI mixed host device shows a maximum external quantum efficiency of 9.1%, which is dramatically improved compared to that of the CBP (6.6%) and TPBI (5.4%) single host devices. Such a mixed host strategy can also be exploited in red phosphor dibenzo[f,h]quinoxaline iridium (acetylacetonate) doped devices. Investigations reveal that the position of charge carrier recombination zone of the mixed host devices predominantly locates in the electron blocking layer/emitting layer interface. The efficiency enhancement is attributed to the optimized hole and electron injection balance and hence increased charge carrier recombination rate in the emitting layer.

“Click” chemistry synthesis of carbazole dendrimer as host material for electrophosphorescent device

A new solution processable dendrimer, with carbazole as a hole transporting unit, was efficiently synthesized based on convergent approach by alternation of Cu-catalyzed azide/alkyne cycloaddition (CuAAC) reaction and Williamson ether synthesis. The orthogonal chemistry completely avoided protection and activation of the focal points in the process of dendrimer synthesis. The dendrimer showed wide bandgap and has good thermal stability. The carbazole dendrimer was studied as electrophosphorescent host materials. Electrophosphorescent devices with the configuration of ITO/PEDOT:PSS/carbazole dendrimer:Ir(ppy)3/TPBI/LiF/Al were fabricated. The device showed turn-on voltage of 5.74V, a maximum current efficiency of 13.7cd/A, a power efficiency of 6.39lm/W and an external quantum efficiency of 5.03%.

Influence of the Performance of Organic Light Emitting Devices by Chemical Reaction at the Interface between Electron Transport Material and Ba Cathode

Red electrophosphorescent organic light-emitting devices using red phosphorescent dopant, and tris-(8-hydroxyquinoline)-aluminum (Alq3) and 2,9-dimethyl-4,7 diphenyl-1,10-phenanthroline (BCP) electron injecting have been fabricated. A device with Alq3 as electron transport layer shows high turn-on voltage (@ 1 cd/m 2 ) of 6.25 V, but a device with BCP does lower turn-on voltage of 5.0 V. Alq3 and BCP have silimar lowest unoccupied molucular obital, 3.0 eV and 2.9 eV, which are the higher values than work function of Ba (2.7 eV). So, Ba cathode does not form energy barrier to inject electron to organic layer from simple energy band of view. However, these devices represent different injection properties, therefore we analyze the interface between organic layer and cathode. X-ray photoelectron spectroscopy depth profiling measurements reveal the strong chemical reaction and bonding of Ba with the C and O present in the Alq3 molecules. Results show that the performance of the electrophosphorescent devices is mainly governed by the structure and the chemical reaction at the interface between Ba metal and electron-injecting material. [doi:10.2320/matertrans.M2010381]

Ladder polysilsesquioxane for wide-band semiconductors: synthesis, optical properties and doped electrophosphorescent device

A ladder polysilsesquioxane with side chain 3-methyl-1,5-diphenylbenzene groups (Tp-LPSQ) is synthesized successfully and confirmed by the MALDI-TOF MS, 29Si-NMR and 1H-NMR. DSC, TGA, AFM and PL spectra reveal its good film-forming property, high thermal and morphological stability and good miscibility to the dopant FIrpic. In addition, it also shows a high triplet energy and a wide bandgap. Thus Tp-LPSQ may act as a host for the blue light emitting iridium complex FIrpic. The electrophosphorescent device based on Tp-LPSQ as the active layer exhibits typical blue emission and the performance of device is superior to other reported polymeric host materials.

Synthesis of ring-structured polysiloxane as host materials for blue phosphorescent device

A ringed polysiloxane with a side chain of dibenzothiophene groups (BS-PSQ) is successfully synthesized as confirmed by MALDI-TOF MS and 1H-NMR. DSC, TGA, AFM and spectra reveal its good film-forming ability, high thermal and morphological stability, and good miscibility with the dopant FIrpic. In addition, it also has a high triplet energy and a wide band gap. The BS-PSQ may be used as a host for the blue light emitter iridium complex FIrpic. The electrophosphorescent device based on BS-PSQ as the active layer exhibits typical blue emission, and the performance of the device is superior to that of any other POSS-based host material reported and also to some of the small molecular host materials.

Highly efficient solution-processed green and red electrophosphorescent devices enabled by small-molecule bipolar host material

Download options Please wait... Supplementary files Supplementary information PDF (115K) Article information DOI https://doi.org/10.1039/C1JM10987A Article type Paper Submitted 07 Mar 2011 Accepted 07 Apr 2011 First published 26 May 2011 Download Citation J. Mater. Chem., 2011,21, 9326-9331 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Highly efficient solution-processed green and red electrophosphorescent devices enabled by small-molecule bipolar host material M. Zhu, T. Ye, X. He, X. Cao, C. Zhong, D. Ma, J. Qin and C. Yang, J. Mater. Chem., 2011, 21, 9326 DOI: 10.1039/C1JM10987A To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Minrong Zhu Tengling Ye Xun He Xiaosong Cao Cheng Zhong Dongge Ma Jingui Qin Chuluo Yang