High-efficiency Organic Light-emitting Diodes Research Articles

Derivative of oxygafluorene and di-tert-butyl carbazole as the host with very high hole mobility for high-efficiency blue phosphorescent organic light-emitting diodes

Derivative of oxygafluorene and di-tert-butyl carbazole was synthesized as the host material for high-efficiency blue phosphorescent organic light-emitting diodes. It exhibited moderate thermal stability with 5% weight loss temperature of 337 °C and glass-forming ability with the glass-transition temperature of 65 °C. The solid-state ionization potential of di-tert-butyl carbazolyl-substituted oxygafluorene was found to be 5.54 eV as established by electron photoemission spectrometry. It showed low-dispersity hole transport with time-of-flight hole mobilities of 10−2 cm2 V−1 s−1 observed at high electric fields. Blue devices based on the synthesized compound showed high external quantum efficiency up to 16.5% and low efficiency roll-off.

Extremely high-efficiency and ultrasimplified hybrid white organic light-emitting diodes exploiting double multifunctional blue emitting layers.

Numerous hybrid white organic light-emitting diodes (WOLEDs) have recently been developed. However, their efficiency is not comparable to that of their best all-phosphorescent WOLED counterparts, and the structures are usually complicated, restricting their further development. Herein, a novel concept is used to achieve a hybrid WOLED, whose crucial feature is the exploitation of double multifunctional blue emitting layers. The three-organic-layer WOLED exhibits a total efficiency of 89.3 and 65.1 lm W–1 at 100 and 1000 cd m–2, respectively, making it the most efficient hybrid WOLED reported in the literature so far. Significantly, the efficiencies of hybrid WOLEDs have, for the first time, been demonstrated to be comparable to those of the best all-phosphorescent WOLEDs. In addition, the device exhibits the lowest voltages among hybrid WOLEDs (i.e., 2.4, 2.7 and 3.1 V for 1, 100 and 1000 cd m–2, respectively). Such remarkable performance achieved from such an ultrasimplified structure opens a new path toward low-cost commercialization.

High-efficiency and superior color-stability white phosphorescent organic light-emitting diodes based on double mixed-host emission layers

We demonstrate high-efficiency and superior color-stability white phosphorescent organic light-emitting diodes based on double blue mixed-host emission layers (EMLs) with different mixed ratios. The key feature of the concept is to introduce double blue mixed-host EMLs with an orange ultrathin layer sandwiched between them. The improved white device without spacer or interlayer achieves superior color-stability and reduced efficiency roll-off, which are consistent with the good ambipolar conductivity of the mixed-host layer. Moreover, peak efficiency of 40.8 lm/W and low turn-on voltage of 2.71 V are realized. The double mixed-host EMLs concept proves to be quite useful in achieving excellent device performance.

Design of C^NN type iridium(iii) complexes towards short-wavelength emission for high efficiency organic light-emitting diodes

The first blue-emitting C^NN based Ir-complex was synthesized and applied to PhOLEDs, with efficiencies of 20.1% and 41.6 cd A−1.

Solution-processed nickel oxide nanoparticles with NiOOH for hole injection layers of high-efficiency organic light-emitting diodes.

Nickel oxide (NiOx) nanoparticles (NPs) were synthesized by a solution-based method and NP films were used as hole injection layers (HILs) in organic light-emitting diodes (OLEDs). To evaluate the hole injection functionality of the NiOx NP HIL, we compared the performance of OLEDs with three types of HILs: spin-coated PEDOT:PSS, thermally evaporated HAT-CN, and spin-coated NiOx NP films. The considerably high component ratio of NiOOH on the air-annealed NiOx NP film surface results in an enhanced hole injection functionality even without UV-ozone treatment. Consequently, the OLEDs using the NiOx NP HILs show significantly higher performances than those of the OLEDs using PEDOT:PSS along with a more than doubled lifetime. Moreover, the OLEDs using the NiOx NP layers show higher external quantum efficiency (EQE), and current and power efficiency values than those of the OLEDs using HAT-CN at a high luminance level. Most notably, the device shows considerably higher current and power efficiency values than those of the recently reported state-of-the-art OLEDs using other types of metal-oxide or metal-based HILs.

High-Efficiency Dicyanobenzene-Based Organic Light-Emitting Diodes Exhibiting Thermally Activated Delayed Fluorescence

We have designed novel thermally activated delayed fluorescence (TADF) materials, 2DMACPN and 2DMACTPN, with 9,9-dimethyl-9,10-dihydroacridine (DMAC) as an electron donor and dicyanobenzene as an electron acceptor. We obtain the zero-zero transition energies of the first excited singlet (S1) and first triplet excited (T1) states of TADF materials by performing density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations on the ground state using a dependence on charge transfer amounts for the optimal Hartree-Fock percentage in the exchange-correlation of TD-DFT. The calculated ΔEST values of 2DMACPN (0.019 eV) and 2DMACTPN (0.023 eV) were smaller than those of 2CzPN (0.363eV) and 2CzTPN (0.178eV) because of the large dihedral angles between the plane of DMAC and the connected phenyl rings of PN and TPN. We show that 2DMACPN would have the highest TADF efficiency among the four compounds because it has the largest dihedral angle, which creates a small spatial overlap between the HOMO and the LUMO, and consequently the smallest ΔEST.

High-Efficiency Bottom-Emitting Organic Light-Emitting Diodes with Double Aluminum as Electrodes**Supported by the Nanjing University of Telecommunications and Posts under Grant Nos NY212010 and NY212034, the National Natural Science Foundation of China under Grant Nos 91233117 and 51333007, the Natural Science Fund in Jiangsu Province under Grant No BK2012834, the National Basic Research Program of China under Grant No 2015CB932200, and

Bottom-emitting organic light-emitting diodes (BOLEDs), using Al/MoO3 as the semitransparent anode and LiF/Al as the reflective cathode and Alq3 as the emitter, are fabricated. At the same time, the performance improvement of the BOLEDs having a capping layer inserted between the semitransparent anode and the glass substrate is studied. The optimized microcavity BOLED shows a current efficiency (5.49 cd/A) enhancement of 10% compared with a conventional BOLED based on ITO (5.0 cd/A). Slight color variation is observed in 120° forward viewing angle with 50 nm BCP as the capping layer. Strong dependence of efficiency on Al anode thickness and the thickness and refractor index of the capping layer is explained. The results indicate that the BOLEDs with the double-aluminum electrode have potential practical applications.

Highly Efficient Near-Infrared Delayed Fluorescence Organic Light Emitting Diodes Using a Phenanthrene-Based Charge-Transfer Compound.

Significant efforts have been made to develop high-efficiency organic light-emitting diodes (OLEDs) employing thermally activated delayed fluorescence (TADF) emitters with blue, green, yellow, and orange-red colors. However, efficient TADF materials with colors ranging from red, to deep-red, to near-infrared (NIR) have been rarely reported owing to the difficulty in molecular design. Herein, we report the first NIR TADF molecule TPA-DCPP (TPA=triphenylamine; DCPP=2,3-dicyanopyrazino phenanthrene) which has a small singlet-triplet splitting (ΔEST ) of 0.13 eV. Its nondoped OLED device exhibits a maximum external quantum efficiency (EQE) of 2.1 % with a Commission International de L'Éclairage (CIE) coordinate of (0.70, 0.29). Moreover, an extremely high EQE of nearly 10 % with an emission band at λ=668 nm has been achieved in the doped device, which is comparable to the most-efficient deep-red/NIR phosphorescent OLEDs with similar electroluminescent spectra.

Enabling high-efficiency organic light-emitting diodes with a cross-linkable electron confining hole transporting material

Wet-process enables flexible, large area-size organic devices to be fabricated cost-effectively via roll-to-roll manufacturing. However, wet-processed devices often show comparatively poor performance due to the lack of solution-process feasible functional materials that exhibit robust mechanical properties. We demonstrate here a cross-linkable material, 3,6-bis(4-vinylphenyl)-9-ethylcarbazole (VPEC), to facilitate the injection of hole and meanwhile effectively confine electron to realize, for examples, high efficiency organic light-emitting diodes, especially at high luminance. The VPEC shows a hole mobility of 1×10−4cm2V−1s−1 and a triplet energy of 2.88eV. Most importantly, the VPEC not only works for devices containing low band-gap red or green emitters, but also for the counterpart with high band-gap blue emitter. With the electron confining hole transporting material, the power efficiency of a studied red device, at 1,000 cdm−2 for example, is increased from 8.5 to 13.5lmW−1, an increment of 59%, and the maximum luminance enhanced from 13,000 to 19,000cdm−2, an increment of 46%. For a high triplet energy blue emitter containing device, it is increased from 6.9 to 8.9lmW−1, an increment of 29%, and the maximum luminance enhanced from 9,000 to 11,000cdm−2, an increment of 22%.

High efficiency organic light-emitting diodes using CuO x /Cu dual buffer layers

An organic light-emitting diode (OLED) device with high efficiency and brightness is fabricated by inserting CuOx/Cu dual inorganic buffer layers between indium-tin-oxide (ITO) and hole-transport layer (HTL). The CuOx/Cu buffer layer limits the operating current density obviously, while the brightness and efficiency are both enhanced greatly. The highest brightness of the optimized device is achieved to be 14 000 cd/m2 at current efficiency of 3 cd/A and bias voltage of 15 V, which is about 50% higher than that of the compared device without CuOx/Cu buffer layer. The highest efficiency is achieved to be 5.9 cd/A at 11.6 V with 3 400 cd/m2, which is almost twice as high as that of the compared device.

Bridging the efficiency gap: fully bridged dinuclear Cu(I)-complexes for singlet harvesting in high-efficiency OLEDs.

The substitution of rare metals such as iridium and platinum in light-emitting materials is a key step to enable low-cost mass-production of organic light-emitting diodes (OLEDs). Here, it is demonstrated that using a solution-processed, fully bridged dinuclear Cu(I)-complex can yield very high efficiencies. An optimized device gives a maximum external quantum efficiency of 23 ± 1% (73 ± 2 cd A(-1) ).

Prediction and design of efficient exciplex emitters for high-efficiency, thermally activated delayed-fluorescence organic light-emitting diodes.

High-efficiency, thermally activated delayed-fluorescence organic light-emitting diodes based on exciplex emitters are demonstrated. The best device, based on a TAPC:DPTPCz emitter, shows a high external quantum efficiency of 15.4%. Strategies for predicting and designing efficient exciplex emitters are also provided. This approach allow prediction and design of efficient exciplex emitters for achieving high-efficiency organic light-emitting diodes, for future use in displays and lighting applications.

나이프 코팅 법으로 제작한 ITO-Free 고전도성 PEDOT:PSS 양극 대면적 유연 OLED 소자 제작에 관한 연구

This paper reports solution-processed, high-efficiency organic light-emitting diodes (OLEDs) fabricated by a knife coating method under ambient air conditions. In addition, indium tin oxide (ITO), traditionally used as the anode, was substituted by optimizing the conductivity enhancement treatment of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films on a polyethylene terephthalate (PET) substrate. The transmittance and sheet resistance of the optimized PEDOT:PSS anode were 83.4% and <TEX>$27.8{\Omega}/sq$</TEX>., respectively. The root mean square surface roughness of the PEDOT:PSS anode, measured by atomic force microscopy, was only 2.95 nm. The optimized OLED device showed a maximum current efficiency and maximum luminous density of 5.44 cd/A and <TEX>$8,356cd/m^2$</TEX>, respectively. As a result, the OLEDs created using the PEDOT:PSS anode possessed highly comparable characteristics to those created using ITO anodes.

A facile route to efficient, low-cost flexible organic light-emitting diodes: utilizing the high refractive index and built-in scattering properties of industrial-grade PEN substrates.

An industrial-grade polyethylene naphthalate (PEN) substrate is explored as a simple, cost-effective platform for high-efficiency organic light-emitting diodes (OLEDs). Its high refractive index, combined with the built-in scattering properties inherent to the industrial-grade version, allows for a significant enhancement in outcoupling without any extra structuring or special optical elements. Flexible, color-stable OLEDs with efficiency close to 100 lm W(-1) are demonstrated.

Reduced efficiency roll-off in phosphorescent OLEDs with a stack emitting layer facilitating triplet exciton diffusion

A high efficiency and low efficiency roll-off phosphorescent organic light-emitting diode (PHOLED) is demonstrated based on a stack emitting layer by alternating [CBP : 4 wt% Ir(ppy)3 (5 nm)] and [CBP : 8 wt% Ir(ppy)3 (5 nm)] ultrathin films.

Synthesis and properties of novel blue-emitting materials: anthracene-based derivatives

Two kinds of novel blue-emitting materials, anthracene-based derivatives, are synthesized by the Suzuki coupling reaction. It is worth noting that the maximum emission wavelengths of the two materials are 441 and 444 nm in tetrahydrofuran and 456 and 454 nm in film states, which are the typical blue fluorescence and the fluorescence quantum yields of them are 0.87 and 1.12 by using 9,10-diphenylanthracene (\Phi_f=0.90) as a calibration standard. The full width at half maximum of them are 56, 55 nm in solution, respectively, presenting good color purity. Both of them display superior thermal properties and electrochemical properties. Scanning electronic microscope results show that the films of two compounds are continuous, compact, and smooth after 100 oC for 3 h. These data indicate their potential to be prepared for high efficiency and long operation lifetime organic light-emitting diodes devices.

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.

A high-efficiency hybrid white organic light-emitting diode enabled by a new blue fluorophor

High-efficiency hybrid white organic light-emitting diode enabled by a new blue fluorophor.

A New Route of Triplet Harvesting for High-Efficiency Organic Light-Emitting Diodes

A New Route of Triplet Harvesting for High-Efficiency Organic Light-Emitting Diodes

High Efficiency Organic Light-Emitting Diode by Ag Anode Technique

The characteristics of a Ag anode with molybdenum oxide (MoOx)-doped N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-diphenyl-1,4′-diamine (α-NPD) are reported. The current efficiency of devices with a Ag anode was achieved over 8.2 cd/A due to the microcavity effect. The current density of the device with a 25% concentration of MoOx was higher than those of a 10% concentration due to the improved charge transfer effect. The device of a Ag anode with a 25% concentration of MoOx indicated an approximate 227% higher current efficiency than that of an ITO anode with a 25% concentration of MoOx. The driving voltage of a Ag anode with a 25% concentration of MoOx was achieved at 4.4V with 10−2 A/cm2.