White Phosphorescent Organic Light-emitting Diodes Research Articles

Synthesis and Electroluminescent Property of New Orange Iridium Compounds for Flexible White Organic Light Emitting Diodes.

Recently, white organic light-emitting diodes (OLEDs) have aroused considerable attention because they have the potential of next-generation flexible displays and white illuminated applications. White OLED applications are particularly heading to the industry but they have still many problems both materials and manufacturing. Therefore, we proposed that the new iridium compounds of orange emitters could be demonstrated and also applied to flexible white OLEDs for verification of potential. First, we demonstrated the chemical properties of new orange iridium compounds. Secondly, conventional two kinds of white phosphorescent OLEDs were fabricated by following devices; indium-tin oxide coated glass substrate/4,4'-bis[N-(napthyl)-N-phenylamino]biphenyl/N,N'-dicarbazolyl-3,5-benzene doped with blue and new iridium compounds for orange emitting 8 wt%/1,3,5-tris[N-phenylbenzimidazole-2-yl]benzene/lithium quinolate/aluminum. In addition, we fabricated white OLEDs using these emitters to verify the potential on flexible substrate. Therefore, this work could be proposed that white light applications can be applied and could be extended to additional research on flexible applications.

Efficient non-doped monochrome and white phosphorescent organic light-emitting diodes based on ultrathin emissive layers

Efficient red, orange, green and blue monochrome phosphorescent organic light-emitting diodes (OLEDs) with simplified structure were fabricated based on ultrathin emissive layers. The maximum efficiencies of red, orange, green and blue OLEDs are 19.3cd/A (17.3lm/W), 45.7cd/A (43.2lm/W), 46.3cd/A (41.6lm/W) and 11.9cd/A (9.2lm/W). Moreover, efficient and color stable white OLEDs based on two complementary colors of orange/blue, three colors of red/orange/blue, and four colors of red/orange/green/blue were demonstrated. The two colors, three colors and four colors white OLEDs have maximum efficiencies of 30.9cd/A (27.7lm/W), 30.3cd/A (27.2lm/W) and 28.9cd/A (26.0lm/W), respectively. And we also discussed the emission mechanism of the designed monochrome and white devices.

M‐Indolocarbazole Derivative as a Universal Host Material for RGB and White Phosphorescent OLEDs

The host materials designed for highly efficient white phosphorescent organic light‐emitting diodes (PhOLEDs) with power efficiency (PE) >50 lm W‐1 and low efficiency roll‐off are very rare. In this work, three new indolocarbazole‐based materials (ICDP, 4ICPPy, and 4ICDPy) are presented composed of 6,7‐dimethylindolo[3,2‐a]carbazole and phenyl or 4‐pyridyl group for hosting blue, green, and red phosphors. Among this three host materials, 4ICDPy‐based devices reveal the best electroluminescent performance with maximum external quantum efficiencies (EQEs) of 22.1%, 27.0%, and 25.3% for blue (FIrpic), green (fac‐Ir(ppy)3), and red ((piq)2Ir(acac)) PhOLEDs. A two‐color and single‐emitting‐layer white organic light‐emitting diode hosted by 4ICDPy with FIrpic and Ir(pq)3 as dopants achieves high EQE of 20.3% and PE of 50.9 lm W−1 with good color stability; this performance is among the best for a single‐emitting‐layer white PhOLEDs. All 4ICDPy‐based devices show low efficiency roll‐off probably due to the excellent balanced carrier transport arisen from the bipolar character of 4ICDPy.

Color stable white phosphorescent organic light emitting diodes with red emissive electron transport layer

We analyzed the performance of multi-emissive white phosphorescent organic light-emitting diodes (PHOLEDs) in relation to various red emitting sites of hole and electron transport layers (HTL and ETL). The shift of the recombination zone producing stable white emission in PHOLEDs was utilized as luminance was increased with red emission in its electron transport layer. Multi-emissive white PHOLEDs including the red light emitting electron transport layer yielded maximum external quantum efficiency of 17.4% with CIE color coordinates (−0.030, +0.001) shifting only from 1000 to 10 000 cd/m2. Additionally, we observed a reduction of energy loss in the white PHOLED via Ir(piq)3 as phosphorescent red dopant in electron transport layer.

Improved color stability of white organic light-emitting diodes without interlayer between red, orange and blue emission layers

We demonstrated color stability improved white phosphorescent organic light-emitting diodes (WOLEDs) based on red, orange and blue emission layers. Iridium(III) Bis(3,5-diflouro)-2-(2-pyridyl)phenyl-(2-carboxypyridyl) was doped into red emission layer (R-EML) and orange emission layer (O-EML) to lower the electrons injection barrier and facilitate the ambipolar charge carriers balance. Consequently, the recombination region was extended to the R-EML and O-EML, leading to the excellently stable spectra and the reduction of triplet–triplet annihilation. Then the resulting device with a negligible Commission International de L'Eclairage coordinates shift of (0.003, 0.007) within a wide luminance range as well as a high color rendering index of 90 was gained, which was comparable to the profit caused by the conventional method of introducing the interlayer. And the emission mechanism of the WOLEDs was also discussed.

Solution-Processed Blue/Deep Blue and White Phosphorescent Organic Light-Emitting Diodes (PhOLEDs) Hosted by a Polysiloxane Derivative with Pendant mCP (1,3-bis(9-carbazolyl)benzene).

The synthesis and characterization is reported of an efficient polysiloxane derivative containing the 1,3-bis(9-carbazolyl)benzene (mCP) moiety as a pendant unit on the polysiloxane backbone. In comparison with mCP, the mCP-polysiloxane hybrid (PmCPSi) has significantly improved thermal and morphological stabilities with a high decomposition temperature (Td = 523 °C) and glass transition temperature (Tg = 194 °C). The silicon-oxygen linkage of PmCPSi prevents intermolecular π-stacking and ensures a high triplet energy level (ET = 3.0 eV). Using PmCPSi as a host, blue phosphorescent organic light emitting devices (PhOLEDs) effectively confine triplet excitons, with efficient energy transfer to the guest emitter and a relatively low turn-on voltage of 5.8 V. A maximum external quantum efficiency of 9.24% and maximum current efficiency of 18.93 cd/A are obtained. These values are higher than for directly analogous poly(vinylcarbazole) (PVK) based devices (6.76%, 12.29 cd/A). Good color stability over a range of operating voltages is observed. A two-component "warm-white" device with a maximum current efficiency of 10.4 cd/A is obtained using a blend of blue and orange phosphorescent emitters as dopants in PmCPSi host. These results demonstrate that well-designed polysiloxane derivatives are highly efficient hosts suitable for low-cost solution-processed PhOLEDs.

Adjusting dopant concentrations in solution process to optimize the white phosphorescent organic light-emitting diodes

In this study, white phosphorescent organic light-emitting diodes (PhOLEDs) have been demonstrated with small molecule by using solution processes. Spin-coating is employed as the way for deposition method. 4,4′-N,N′-dicarbazole-biphenyl (CBP) which is typical small molecule based ink is used for spin-coating method, and three phosphorescent dopants materials, Firidium(III) bis[(4,6-difluoro phenyl)-pyridinato-N,C2′] picolinate (FIrpic), bis[1-(phenyl) isoquinoline) iridium(III) acetyl acetonate (Ir(piq)2 (acac))], and iridium(III) tris(2-phenylpy-ridine) (Ir(ppy)3) were prepared. For spin-coating processes, various parameters properties were investigated including materials concentrations, solvents effect, and electron transporting materials to get high efficiency and white color of white PhOLED device. As a result, the precisely controlled solution processes could be a promising technology for solution process can be a good alternative of vacuum deposition technology.

Doping-free orange and white phosphorescent organic light-emitting diodes with ultra-simply structure and excellent color stability

We demonstrate simplified doping-free orange phosphorescent organic light-emitting diodes (OLEDs) based on ultrathin emission layer. The optimized orange device has the maximum current efficiency of 52.1cd/A and power efficiency of 36.3lm/W, respectively. Efficient simplified doping-free white OLEDs employing blue and orange ultrathin emission layers have excellent color stability, which is attributed to the avoidance of the movement of charges recombination zone and no differential color aging. One white device exhibits high efficiency of 33.6cd/A (30.1lm/W). Moreover, the emission mechanism of doping-free orange and white OLEDs is also discussed.

Improved performance for white phosphorescent organic light-emitting diodes utilizing an orange ultrathin non-doped emission layer

The chemical structures of materials, the device structures (a) and the detailed energy level diagram of the materials (b).

Spiro[fluorene-9,9′-xanthene]-based universal hosts for understanding structure–property relationships in RGB and white PhOLEDs

Independent and accumulative modification of frontier molecular orbital energy levels without affecting the triplet energy level can be realized.

Study of triplet exciton’s energy transfer in white phosphorescent organic light-emitting diodes with multi-doped single emissive layer

The performance of three color single emissive layer white phosphorescent organic light-emitting diodes (PHOLEDs), with different hole transporting materials of N,N′-diphenyl-N,N′-bis(l-naphthyl-phenyl)-(l,l′-biphenyl)-4,4′-diamine (NPB), 4,4_,4_-tris_N-carbazolyl_tri-Phenylamine (TCTA) and 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), was analyzed. It is found that the luminous efficiency of white PHOLEDs is closely related to the triplet exciton energy level in the hole transporting layer (HTL). White PHOLEDs with a TAPC as HTL, having the highest triplet exciton energy level amongst the three different hole transporting materials, yielded external quantum efficiency of 25.5% at 4.5V and a high luminous efficiency of 51cd/A at 4.5V with CIE color coordinates of (0.34, 0.39) at 10V. The results reveal that the effective confinement of triplet excitons in white PHOLEDs with a high triplet exciton energy level HTL (TAPC) allows improving the luminous efficiency, as compared to the devices made with NPB and TCTA. Additionally, we demonstrated possibility for the loss of intensity in EL spectra of the white PHOLED devices with NPB and TCTA as HTL compared to that of the device with TAPC as HTL.

Donor–acceptor type material as a triplet host for high efficiency white phosphorescent organic light-emitting diodes

Highly efficient white phosphorescent organic light-emitting diodes (OLEDs) were reported using a donor–acceptor type material as a host material. A donor–acceptor type material, 10-phenyl-10H-spiro[acridine-9,9′-fluorene]-2′,7′-dicarbonitrile (ACRFLCN), was doped with a yellow emitting iridium(III) bis(4-phenylthieno[3,2-c]pyridinato-N,C2′) acetylacetonate (PO-01) dopant and high quantum efficiency of 26.9% was realized in the yellow phosphorescent OLEDs using the ACRFLCN host material. Efficient energy transfer and bipolar charge transport properties of ACRFLCN increased the quantum efficiency of the PO-01 doped yellow phosphorescent OLEDs. In addition, white phosphorescent OLEDs with the PO-01 doped ACRFLCN yellow emitting layer exhibited a high quantum efficiency of 22.8% and a high power efficiency above 50.0lm/W.

Study of sequential dexter energy transfer in high efficient phosphorescent white organic light-emitting diodes with single emissive layer.

In this study, we report our effort to realize high performance single emissive layer three color white phosphorescent organic light emitting diodes (PHOLEDs) through sequential Dexter energy transfer of blue, green and red dopants. The PHOLEDs had a structure of; ITO(1500 Å)/NPB(700 Å)/mCP:Firpic-x%:Ir(ppy)3-0.5%:Ir(piq)3-y%(300 Å)/TPBi(300 Å)/Liq(20 Å)/Al(1200 Å). The dopant concentrations of FIrpic, Ir(ppy)3 and Ir(piq)3 were adjusted and optimized to facilitate the preferred energy transfer processes attaining both the best luminous efficiency and CIE color coordinates. The presence of a deep trapping center for charge carriers in the emissive layer was confirmed by the observed red shift in electroluminescent spectra. White PHOLEDs, with phosphorescent dopant concentrations of FIrpic-8.0%:Ir(ppy)3-0.5%:Ir(piq)3-0.5% in the mCP host of the single emissive layer, had a maximum luminescence of 37,810 cd/m2 at 11 V and a luminous efficiency of 48.10 cd/A at 5 V with CIE color coordinates of (0.35, 0.41).

All-phosphorescent three-color two-stack tandem white organic light emitting diodes with high-color-rendering index values

Reported herein are high-color-rendering index two-stack phosphorescent tandem white organic light-emitting diodes using three-color phosphorescent dopants: iridium(III) bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl) (472 nm) as a blue emitter for the first stack layer, and iridium(III) bis(4-methyl-2-(3,5-dimethylphenyl)quinolinato-N,C2′) tetramethylheptadionate (612 nm) and iridium(III) bis(4-(4-tbutylphenyl)thieno[3,2-c]pyridinato-N,C2′)acetylacetonate (562 nm) as red and yellow triplet emitters for the second stack layer, respectively. By locating the blue and red emissive layers slightly far from their antinode position in terms of photonic mode density, the electroluminescent spectra could be changed, and the CRI values could be increased from 74 to over 85. There is some efficiency loss, however, from 38.6 to 29.4 lm/W due to the inevitable electrical and optical losses.

Phosphorescent white organic light-emitting diodes by electron transporting layer engineering.

The authors describe the fabrication of white organic light-emitting diodes (WOLEDs) with dual electron transporting layers (D-ETL) using 2,9-dimethyl-4,7-diphenyl-1,10-phenanhroline/ 4,7-diphenyl-1,10-phenanthroline (BPhen) and bis-(2-methyl-8-quinolinolate)-4-(phenylphenolato) aluminum/BPhen. Stepwise D-ETL easily transports electrons easily to the emitting layer and reduces the leakage of electrons. Therefore, WOLEDs with D-ETL show higher external quantum efficiency (EQE) when compared to a control WOLED with a single ETL device. The optimized WOLEDs showed a peak EQE of 13.0%, luminous efficiency of 27.4 cd/A, and Commission Internationale de L'Eclairage coordinates of (0.40, 0.39) at 1000 cd/m2.

A solution-processable triphenylamine-fluorene host for exciplex based white phosphorescent organic light-emitting diodes

Download options Please wait... Supplementary files Supplementary information PDF (207K) Article information DOI https://doi.org/10.1039/C4TC01870B Article type Paper Submitted 21 Aug 2014 Accepted 22 Sep 2014 First published 29 Sep 2014 Download Citation J. Mater. Chem. C, 2014,2, 9754-9759 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions A solution-processable triphenylamine-fluorene host for exciplex based white phosphorescent organic light-emitting diodes Z. Fan, N. Li, Y. Quan, Q. Chen, S. Ye, Q. Fan, W. Huang and H. Xu, J. Mater. Chem. C, 2014, 2, 9754 DOI: 10.1039/C4TC01870B 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. Social activity Tweet Share Search articles by author Zhaokang Fan Nengquan Li Yiwu Quan Qingmin Chen Shanghui Ye Quli Fan Wei Huang Hui Xu

P‐159: Triplet Exciton Confinement in White Phosphorescent Organic Light‐Emitting Diodes with Multi‐Doped Single Emissive Layer

AbstractWe fabricated white phosphorescent organic light‐emitting diodes (PHOLEDs) with the primary color(Red, Green and Blue) in single emissive layer using NPB, TCTA and TAPC as hole transporting layer (HTL) having different triplet energy level to observe triplet exciton's behavior. White PHOLED with TAPC having higher triplet energy level shows 51cd/A of luminous efficiency, and CIEXY color coordinate of (0.35, 0.40) at 10V.

High external quantum efficiency in yellow and white phosphorescent organic light-emitting diodes using an indoloacridinefluorene type host material

High efficiency yellow phosphorescent organic light-emitting diodes were developed using spiro[fluorene-9,8′-indolo[3,2,1-de]acridine]-2,7-dicarbonitrile (ACDCN) as the host material for yellow emitting iridium(III) bis(4-phenylthieno[3,2-c]pyridinato-N,C2′)acetylacetonate (PO-01). The ACDCN host showed bipolar charge transport properties and efficient energy transfer to PO-01 dopant. Maximum external quantum efficiency of 25.7% and external quantum efficiency of 21.9% at 1000cd/m2 were obtained using ACDCN as the host material. In addition, high external quantum efficiency of 20.9% was achieved in the two color white phosphorescent organic light-emitting diodes with the PO-01 and iridium(III) bis[(4,6-difluorophenyl)-pyridinato-N,C2]picolinate doped ACDCN emitting layer.

Single emissive layer white phosphorescent organic light-emitting diodes based on solution-processed iridium complexes

We fabricated efficient, white phosphorescent organic light-emitting diodes (WPhOLEDs) with all of blue, yellow, and deep-red iridium(III) complexes doped in 4,4′,4″-tris(cabazol-9-yl)triphenylamine [or 1,3-bis(carbazol-9-yl)benzene)]:poly(9-vinylcarbazole):1,3-bis[2-(4-tert-butylphenyl)-1,3,4,-oxadiazo-5-yl] mixed-host system and investigated their photophysical, electrochemical, and electroluminescent properties. An optimal combination of blue, yellow, and deep-red iridium(III) complexes improved the charge balance and triplet excitons confinement in the emitting layer. We fabricated the WPhOLEDs with a configuration of indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (40 nm)/emitting layer (50–60 nm)/1,3,5-tri[(3-pyridyl)-phen-3-yl]benzene (20 nm)/lithium fluoride (1 nm)/aluminum (150 nm). In terms of performance, the WPhOLEDs exhibited a maximum luminance efficiency of 23.04 cd/A and external quantum efficiency of 11.45%.

New universal bipolar host materials with fluorene as non-conjugated bridge for multi-color electrophosphorescent devices

Two novel bipolar hosts (CzFCN2 and CzDFCN) comprising a hole-transport carbazole donor and electron-transport cyano-substituted fluorene acceptor have been synthesized, and their thermal, photophysical, and electrochemical properties were characterized. The non-conjugated linkage between the carbazole donor and the cyano-substituted fluorene acceptor provides excellent thermal/morphological properties and high triplet energies (ET=2.86 eV) for both CzFCN2 and CzDFCN. These bipolar hosts also exhibited reversible redox behavior, which makes them good candidates for the host material in efficient phosphorescent organic light-emitting diode (PhOLED) devices. Multi-color PhOLED devices incorporating CzFCN2 and CzDFCN as the universal host achieved maximum external quantum efficiencies (ηext) as high as 10.7, 17.0, 17.2, and 17.6% for blue, green, yellow, and red devices, respectively. In addition, three-component white PhOLEDs (WOLEDs) based on CzFCN2 and CzDFCN as host materials exhibited high color stabilities with ηext as high as 10.5 and 12.4% and power efficiencies (ηp) of 20.5 and 26.7 lm W−1, respectively.