Efficient Phosphorescent OLEDs Research Articles

Highly efficient orange phosphorescent organic light-emitting diodes based on an iridium(iii) complex with diethyldithiocarbamate (S^S) as the ancillary ligand

A novel iridium(iii) complex Ir(dpp)2(dta) with diethyldithiocarbamate (S^S) as the ancillary ligand was synthesized and characterized. The polymer organic light-emitting device based on Ir(dpp)2(dta) has been fabricated.

Highly efficient green phosphorescent organic light-emitting diodes with low efficiency roll-off based on iridium(iii) complexes bearing oxadiazol-substituted amide ligands

This manuscript describes the highly efficient OLEDs with low efficiency roll-off based on iridium(iii) complexes bearing oxadiazol-substituted amide ligands.

A novel spiro-annulated host based on carbazole with good thermal stability and high triplet energy for efficient blue and green phosphorescent organic light-emitting diodes

A novel spiro-annulated host based on carbazole was synthesized and fully characterized. The thermal, photophysical and electrochemical properties of this host material were investigated. The host exhibited good thermal stabilities with a decomposition temperature of 427 °C and also exhibited excellent morphological properties. A high triplet energy (2.90 eV) was obtained for the host due to its spiro-annulated structure. This host was proved to be effective for both blue and green phosphorescent organic light-emitting diodes. Four different blue devices were fabricated with the best performance that a maximum current efficiency of 12.2 cd A−1 and a maximum power efficiency of 8.8 lm W−1. The performance of the host was better than that of 4,4′-bis(9-carbazolyl)-biphenyl which is the benchmark host material in green PHOLED devices.

Solution-processable bipolar hosts based on triphenylamine and oxadiazole derivatives: Synthesis and application in phosphorescent light-emitting diodes

Host material with enhanced and balanced charge injection/transport is essential for efficient phosphorescent organic light-emitting diodes (PhOLEDs). We synthesized two new bipolar hosts, TPA-2OXD and TPA-3OXD, composed of hole-transporting triphenylamine core linked with two and three electron-transporting aromatic 1,3,4-oxadiazole derivatives respectively, aiming to enhance and balance charge injection and transport. They revealed good thermal stability (Td>300°C, Tg>100°C) and homogeneous films were readily obtained by spin-coating process (roughness<0.9nm). Multilayer PhOLEDs (ITO/PEDOT:PSS/EML/BCP/LiF/Al) have been successfully fabricated using Ir(ppy)3-doped hosts as emitting layer (EML). The maximum luminance and maximum current efficiency of TPA-2OXD-based device were 8190cd/m2 and 4.50cd/A, much higher than 6299cd/m2 and 1.53cd/A respectively of TPA-3OXD-based one. This has been ascribed to more appropriate ratio (2/1) of electron-/hole-transporting moieties in TPA-2OXD. The TPA-2OXD also excels conventional host PVK in terms of device performance (5774cd/m2, 1.91cd/A). Moreover, the turn-on voltages of TPA-2OXD- and TPA-3OXD-based devices were 4.3V and 5.5V respectively, much lower than 7.4V of PVK-based one. Current results indicate that the bipolar TPA-2OXD and TPA-3OXD are promising host materials capable of being fabricated by wet processes.

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.

Solution-Processed Phosphorescent Organic Light-Emitting Diodes with Ultralow Driving Voltage and Very High Power Efficiency.

To realize power efficient solution-processed phosphorescent organic light-emitting diodes (s-PhOLEDs), the corresponding high driving voltage issue should be well solved. To solve it, efforts have been devoted to the exploitation of novel host or interfacial materials. However, the issues of charge trapping of phosphor and/or charge injection barrier are still serious, largely restraining the power efficiency (PE) levels. Herein, with the utilization of an exciplex-forming couple 4, 4′, 4″ -tris[3-methylphenyl(phenyl)amino]triphenylamine (m-MTDATA) and 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene (TmPyPB), the efficient charge injection and transporting, barrier-free hole-electron recombination for the formation of the interfacial exciplex, and elimination of charge traps of phosphors in the emissive layer are realized simultaneously, resulting in a turn-on voltage of 2.36 V, a record high PE of 97.2 lm W−1, as well as extremely low driving voltage of 2.60 V at 100 cd m−2, 3.03 V at 1000 cd m−2 and 4.08 V at 10000 cd m−2. This report is the first time that the PE performance of s-PhOLED approaches 100 lm W−1 high level, even superior to the corresponding state-of-the-art performance of the same color vacuum-deposited PhOLED (v-PhOLED) counterpart. We anticipate this report opens a new avenue for achieving power efficient monochromatic and white s-PhOLEDs with simple structures.

Highly efficient solution-processed pure red phosphorescent organic light-emitting diodes using iridium complexes based on 2,3-diphenylquinoxaline ligand

We synthesized two highly efficient red phosphorescent Ir(III) complexes, bis[2,3-diphenylquinoxalinato-N,C2′]iridium(III) pyrazinate (dpq)2Ir(prz) (1) and bis[2,3-diphenylquinoxalinato- N,C2′]iridium(III) 5-methylpyrazinate (dpq)2Ir(mprz) (2), which are both based on the use of 2,3-diphenylquinoxaline as the ligand, and investigated their photophysical, electrochemical, and electroluminescence (EL) properties. Both Ir(III) complexes are soluble in common organic solvents and uniform thin films can be readily spin-coated onto substrates. Phosphorescent organic light-emitting diodes (PhOLEDs) produced using the ITO/PEDOT:PSS/TCTA:TPBi:Ir(III) complex/cathode configuration, had a maximum external quantum efficiency of 7.32% and a luminance efficiency of 7.15 cd/A with a CIE coordinate of (0.70, 0.30) for compound 2. CIE coordinates remained stable on increasing current density. To the best of our knowledge, the efficiencies of these PhOLEDs are higher than those previously reported for solution-processed pure red PhOLEDs.

High-Efficiency Blue Phosphorescence Organic Light-Emitting Diode with Ambipolar Carbazole–Triazole Host

An ambipolar material with a high triplet energy of 3.1 eV, 9-(2-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)phenyl)-9H-carbazole (CbzTAZ), was synthesized by conjugating an electron-transporting 1,2,4-triazole and a hole-transporting carbazole and employed as the host doping with blue emitter iridium(III)bis[4,6-(difluorophenyl)-pyridinato-N,C2′]picolinate (FIrpic) to be the emitting layer (EML) of an efficient blue phosphorescent organic light-emitting diode (PhOLED). By adjusting the ratio between CbzTAZ and FIrpic, an efficient OLED performance with a current efficiency (ηC) of 50 cd/A and an external quantum efficiency (ηEQE) of 23.8% can be obtained. The position of the recombination zone located inside the EML close to the electron-transporting layer (ETL) can be detected by partially doping FIrpic in one of the three EML regions. By fine-tuning the thickness of the ETL to balance electrons and holes in the EML, a highly efficient blue PhOLED with a maximum ηC of 52.1 cd/A, a maximum power efficiency of 46...

28.1: Invited Paper: Triplet‐Energy Control of PAHs by Heteroatom Incorporation for Development of Efficient Materials for PHOLEDs

The triplet‐energy control of polycyclic aromatic hydrocarbons (PAHs) was achieved by heteroatom incorporation. For instance, 4b‐aza‐12b‐boradibenzo[g,p]chrysene showed a much larger ET value than the corresponding PAH, dibenzo[g,p]chrysene, and enable us to built phosphorescent organic light‐emitting diodes (PHOLEDs) of high performance. We have also synthesized a variety of heteroatom‐incorporated polycyclic aromatics with a large ET value, which improved not only efficiency of PHOLED but also lifetime.

A host material consisting of phosphinic amide for efficient sky-blue phosphorescent organic light-emitting diodes

A new bipolar host material (PBCz-PO) consisting a phosphinic amide is developed to show a resonance effect. It possesses quite high triplet energy (2.76eV), and this high triplet energy make it suitable to be blue host in phosphorescent organic light-emitting diodes (PHOLEDs). The device with PBCz-PO as a host and FIrpic as a dopant achieved a maximum current efficiency (ηc) of 31.5cd/A, a maximum power efficiency (ηp) of 31.0lm/W and a maximum external quantum efficiency (EQE) of 13.4% as well as low driving voltage.

Macrospirocyclic oligomer based on triphenylamine and diphenylphosphine oxide as a bipolar host for efficient blue electrophosphorescent organic light-emitting diodes (OLEDs).

A novel bipolar oligomer (TPA-PO)3 was prepared as a host material for efficient blue phosphorescent organic light-emitting diodes (OLEDs). Through the C-9s of the fluorene units, three triphenylamine units attached to diphenylphosphine oxide are connected in series to form a macrocyclic structure. The solution-processed phosphorescent device based on FIrpic and (TPA-PO)3 achieved a maximum current efficiency of 19.4 cd A(-1) and a maximum luminance of 11,500 cd m(-2) with a relatively low efficiency roll-off.

New bioinspired hole injection/transport materials for highly efficient solution-processed phosphorescent organic light-emitting diodes

A new concept to supramolecular assembly of existed functional polymers, capable of forming network-like organizational clusters through multiple hydrogen-bonding interactions has been exploited. In this paper, a new adenine-based poly(triphenylamine-carbazole) (PTC-A) has been prepared which exhibits a high self-complementary ability in solution and solid states owing to the formation of adenine–adenine (A–A) pairs by induced hierarchical self-assembly. Comparing with uracil-substituted PTC sample (PTC-U), PTC-A presents a much higher thermal stability, electrochemical stability and solvent-resistance ability due to the formation of the more stable physically cross-linking structure. When the PTC-A is utilized as a hole injection/transport layer in a trilayer OLED device, a remarkable improvement in performance relative to the control PTC and PTC-U under similar experimental conditions has been achieved. Further comparison with a control device using a conventional PEDOT:PSS, the efficiency of the solution-processed phosphorescent PLED device with PTC-A is significantly higher than those of PTC-U and PEDOT:PSS-based devices. Thus, PTC-A represents the next-generation hole injection/transport material for high efficiency LED device and low-cost fabrication process.

Highly efficient yellow phosphorescent organic light-emitting diodes with novel phosphine oxide-based bipolar host materials

Highly efficient yellow OLEDs based on bipolar host materials show a maximum current efficiency of 68.28 cd A−1, a maximum external quantum efficiency of 21.3% and a maximum power efficiency of 50.90 lm W−1 with low efficiency roll-off.

9,9-Diphenyl-thioxanthene derivatives as host materials for highly efficient blue phosphorescent organic light-emitting diodes

A series of 9,9-diphenyl-9H-thioxanthene derivatives are reported as host materials in blue phosphorescent OLEDs, giving a maximum power efficiency of 69.7 lm W−1 and an external quantum efficiency of 29.0%.

Mo-doped GZO films used as anodes or cathodes for highly efficient flexible blue, green and red phosphorescent organic light-emitting diodes

We propose a novel transparent conductive oxide constructed by doping molybdenum into gallium zinc oxide (GZO).

Correlation of the molecular structure of host materials with lifetime and efficiency of blue phosphorescent organic light-emitting diodes.

Bicarbazole derivatives, 9,9'-bis(dibenzo[b,d]thiophen-2-yl)-9H,9'H-3,3'-bicarbazole (BCzDBT), 9,9'-bis(dibenzo[b,d]furan-2-yl)-9H,9'H-3,3'-bicarbazole (BCzDBF), and 9,9'-di([1,1'-biphenyl]-3-yl)-9H,9'H-3,3'-bicarbazole (BCzBP), were designed and examined as the hole transport type host materials of the tris[1-(2,4-diisopropyldibenzo[b,d]furan-3-yl)-2-phenylimidazole] (Ir(dbi)3) blue triplet emitter. BCzDBT performed better than BCzDBF and BCzBP as the hosts of Ir(dbi)3 and could demonstrate 24.8% quantum efficiency and long lifetime in the blue phosphorescent devices. Strong hole carrying properties of the bicarbazole derivatives were proposed as the main factors for the high quantum efficiency of the BCzDBT devices, and thermal and chemical stability of BCzDBT were suggested as crucial factors for the long lifetime of the BCzDBT devices.

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.

Highly Efficient Bipolar Host Materials with Indenocarbazole and Pyrimidine Moieties for Phosphorescent Green Light-Emitting Diodes

In this paper, we report bipolar host materials, 6-(2,6-diphenyl-pyrimidin-4-yl)-12,12-dimethyl-6,12,12′-trihydroindeno[1,2-b]carbazole (DPICz1) and 6-(2,6-diphenyl-pyrimidin-4-yl)-12,12-dimethyl-6,12,12′-trihydroindeno[1,2-b]carbazole (DPICz2), with indenocarbazole moiety as a hole-transporting unit and pyrimidine moiety as an electron-transporting unit for highly efficient green phosphorescent organic light-emitting diodes. The synthesized materials show excellent electro-optical properties. Similarly, it also exhibits outstanding thermal and morphological stability due to high glass transition temperature (Tg) of 161 °C and decomposition temperature (Td) of 327–401 °C. Fabricated green phosphorescent organic light-emitting diode shows excellent current and power efficiency of 77.8 cd/A and 62.8 lm/W as well as almost ideal external quantum efficiency of 22.3% at the brightness of 1000 cd/m2.

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).

Efficient blue phosphorescent organic light emitting diodes with host engineering

We demonstrate as much as possible blue color and high efficiency phosphorescent organic light-emitting diodes (PHOLEDs) by using well-known iridium(III)bis[(3,5-difluoro-4-cyanophenyl)-pyridinato-N,C′]picolinate (FCNIrpic) dopant and previously reported good host materials. For the control of blue color and efficiency, various host materials, 1,3-bis(carbazole-9-yl)benzene (mCP), 9-(3-(9H-carbazole-9-yl)phenyl)-3-(dibromophenylphosphoryl)-9H-carbazole (mCPPO1), and 2,8-di(9H-carbazol-9-yl)dibenzo[b,d]furan (DFCz), bis(4-(N-carbazole)phenyl)dimethylsilane (2MCBP) are selected and investigated their performances. A maximum external quantum efficiency (EQE) of 23.9% and power efficiency of 30.2 lm/W are achieved from 2MCBP device with Commision Internationale de L'Eclairage color coordinates (CIEx,y) of (0.14, 0.21). The deepest color with color coordinate of (0.14, 0.19) is obtained for the mCP device.