Single-layer Organic Light-emitting Devices Research Articles

Acyclic, Linear Oligo-meta-phenylenes as Multipotent Base Materials for Highly Efficient Single-layer Organic Light-emitting Devices.

Oligo-meta-phenylenes have been designed and synthesized as multipotent base materials of single-layer organic light-emitting devices. Simple molecular structures of oligo-meta-phenylenes composed of linear phenylene arrays benefited from the wealth of modern reactions available for biaryl couplings and were concisely synthesized in a series. Structure-performance relationship studies with the first seven congeners revealed key features important for the multipotent materials in single-layer devices. As a result, highly efficient phosphorescent electroluminescence was made possible in a highly simplified device architecture comprising one-region, single-layer configurations. Detailed investigations with hole-only devices disclosed that the hole mobility was effectively retarded by potent materials, which should facilitate hole/electron recombination for electroluminescence.

Single-Layer Organic Light-Emitting Devices with C<sub>60</sub> and MoO<sub>3</sub> Mixed Materials as Hole Injection Layer

Single-Layer Organic Light-Emitting Devices with C<sub>60</sub> and MoO<sub>3</sub> Mixed Materials as Hole Injection Layer

Magneto-electroluminescence effects in the single-layer organic light-emitting devices with macrocyclic aromatic hydrocarbons

Magneto-electroluminescence (MEL) effects are observed in single-layer organic light-emitting devices (OLEDs) comprising only macrocyclic aromatic hydrocarbons (MAHs). The fluorescence devices were prepared using synthesized MAHs, namely, [n]cyclo-meta-phenylene ([n]CMP, n = 5, 6). The MEL ratio of the resulting OLED is 1%–2% in the spectral wavelength range of 400-500 nm, whereas it becomes negative (−1.5% to −2%) in the range from 650 to 700 nm. The possible physical origins of the sign change in the MEL are discussed. This wavelength-dependent sign change in the MEL ratio could be a unique function for future single-layer OLEDs capable of magnetic-field-induced color changes.

Dramatic efficiency improvement in single-layer orange phosphorescent organic light-emitting devices with suppressed efficiency roll-off

We have successfully demonstrated efficient single-layer organic light-emitting devices (OLEDs) with a current efficiency of 31.38 cd A−1.

Modular Synthesis of Aromatic Hydrocarbon Macrocycles for Simplified, Single-Layer Organic Light-Emitting Devices

A method for the modular synthesis of aromatic hydrocarbon macrocycles has been developed for base materials in single-layer organic light-emitting devices. The method with Ir-catalyzed direct C-H borylation and Suzuki-Miyaura coupling was concise and scalable, which allowed for a gram-scale preparation of aromatic hydrocarbon macrocycles that have bulky substituents at the periphery. The new arylated hydrocarbon macrocycles enabled a quantitative electro-optical conversion in organic light-emitting devices with a phosphorescent emitter, which is, notably, in a single-layer architecture consisting of two regions of doped and undoped materials. The highest external quantum efficiencies reached 24.8%, surpassing those of previous hydrocarbon base materials.

Efficient saturated red electrophosphorescence by using solution-processed 1-phenylisoquinoline-based iridium phosphors with peripheral functional encapsulation

A series of saturated-red emitting iridium complexes with bifunctional charge-transporting peripheral groups were designed and synthesized. The relationship between the structures and their photophysical, electrochemical and electrophosphorescent properties was investigated. Through the incorporation of hole-transporting triphenylamine units and/or electron-transporting phosphine oxide groups to the cyclometalating ligand, the new complexes exhibited good thermal stabilities with high glass-transition temperatures up to 284°C, while maintained the saturated-red emission of the center core. Besides, the peripheries sufficiently protect the emissive core from the intermolecular interactions. Solution-processed single-layer phosphorescent organic light-emitting device (PhOLED) based on phosphor R2 showed a maximum external quantum efficiency of 7.6% with Commission Internationale de l’Eclairage coordinates of (0.68, 0.30).

Material alternative to ITO for transparent conductive electrode in flexible display and photovoltaic devices

The mechanical stability of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films spin coated onto a UV treated PET substrate was investigated. It was found that the UV exposure modifies the PET surface and improves the wetting conditions for PEDOT:PSS films deposition. The adhesion strength of PEDOT:PSS to UV treated PET surface was found to be 50N/cm2 versus 19N/cm2 to the untreated one. Furthermore, the resistance change of PEDOT:PSS on UV treated PET at 20,000 cycles of bending was measured to be only 3.8%. In contrast, the same polymeric films on untreated PET exhibit 8.7% resistance change and the conventional indium tin oxide (ITO) electrode 23.5%, which demonstrates the superior flexibility of the UV PET/PEDOT:PSS electrodes. The transparency of the produced coatings is 81%. Single layer organic light-emitting device with MEH-PPV electroluminescent polymer was successfully fabricated on UV PET/PEDOT:PSS. The electrical measurements indicate the possibility of using UV PET/PEDOT:PSS as a transparent electrode system, replacing ITO in the flexible optoelectronic devices.

单层有机电致发光器件的阳极修饰研究

ITO anode was modified utilizing UV-ozone or plasma technique and applied to fabricate single-layer organic light-emitting devices( SLOLEDs). The effects of the two methods on the device performance were researched. The experiment results indicate that the devices with plasma modifying manifest better performance than the devices with UV-ozone modifying. Based on plasma technique,further,two sort of buffer material Mo O3 and HAT-CN were introduced to fabricate SLOLEDs. As a result,the devices using HAT-CN as buffer material denote better performance.

Constructing a novel single-layer white organic light-emitting device through a new sky-blue fluorescent bipolar host

A novel device concept was realized for simple single-layer small-molecule white organic light emitting devices. The single organic active layer here is simply comprised of a newly synthesized sky-blue fluorescent bipolar host (TPASO) and a common orange phosphorescent dopant. Suppressed singlet Föster energy transfer induced by a low-concentration doping and spontaneous high- to low-lying triplet energy transfer, respectively, lead to sky-blue fluorescence from TPASO and orange phosphorescence from the dopant. The resulting two-organic-component device exhibits a low turn-on voltage of 2.4V, maximum current/power efficiencies up to 11.27±0.02cdA−1 and 14.15±0.03lmW−1, and a warm-white CIE coordinate of (0.42, 0.45) at 1000cdm−2.

A Bipolar Transporter as an Efficient Green Fluorescent Emitter and Host for Red Phosphors in Multi‐ and Single‐Layer Organic Light‐Emitting Diodes

Multifunctional donor-acceptor compound 4,4'-bis(dibenzothiophene-S,S-dioxide-2-yl)triphenylamine (DSTPA) was obtained by linking a strongly electron-withdrawing core and a strongly electron-donating core with a biphenyl bridge in linear spatial alignment. DSTPA not only has suitable HOMO and LUMO levels for easily accepting both holes and electrons, it was also demonstrated to have a high fluorescence quantum yield of 0.98 and a high triplet energy level of 2.39 eV. Versatile applications of DSTPA for bipolar transport, green fluorescent emission, and sensitizing a red phosphor were systematically investigated in a series of multi- and single-layer organic light-emitting devices. In traditional multilayer devices, it shows excellent performance both in an undoped fluorescent device (used as a green emitter and achieving maximum current and power efficiencies (CE and PE) of 12.6 cd A(-1) and 9.4 Lm W(-1) , respectively) and in a red phosphorescent device (used as a host and achieving maximum CE and PE of 26.4 cd A(-1) and 26.3 Lm W(-1) , respectively). Furthermore, DSTPA was also simultaneously used as an emitter, a hole transporter, and an electron transporter in a single-layer device showing CE and PE of 5.1 cd A(-1) and 4.7 Lm W(-1) , respectively. A single-layer red phosphorescent device with efficiencies of 11.7 cd A(-1) and 12.6 Lm W(-1) was obtained by doping DSTPA with a red phosphor. The performances of all of the devices in this work are comparable to the best of their corresponding classes in the literature.

Highly efficient single-layer organic light-emitting devices based on a bipolar pyrazine/carbazole hybrid host material

High efficiency blue (F), green (P), orange (P) and F–P hybrid warm white single-layer OLEDs are fabricated through a simple manufacturing process.

Highly efficient single-layer organic light-emitting devices using cationic iridium complex as host

Highly efficient single-layer organic light-emitting devices (OLEDs) based on blended cationic Ir complexes as emitting layer have been demonstrated using narrow band gap cationic Ir complex [Ir(Meppy)2(pybm)](PF6) (C1) as guest and wide band gap cationic Ir complex [Ir(dfppy)2(tzpy-cn)](PF6) (C2) as host. As compared with single cationic Ir complex emitting layer, these host–guest systems exhibit highly enhanced efficiencies, with maximum luminous efficiency of 25.7cd/A, external quantum efficiency of 8.6%, which are nearly 3-folds of those of pure C1-based device. Compared with a multilayer host-free device containing C1 as emitting layer and TPBI as electron-transporting and hole-blocking layer, the above single-layer devices also show 2-folds enhancement efficiencies. The high efficiencies achieved in these host–guest systems are among the highest values reported for ionic Ir complexes-based solid-state light-emitting devices. In addition, a white-similar emission with CIE of (0.36, 0.47) has also been achieved with luminous efficiency of 4.2cd/A as the C1 concentration is 0.1wt.%. The results demonstrate that the ionic Ir complexes-based host–guest system provides a new approach to achieve highly efficient OLEDs upon single-layer device structure and solution-processing technique.

Organic Electroluminescent Sensor for Pressure Measurement

We have proposed a novel concept of a pressure sensor called electroluminescent pressure sensor (ELPS) based on oxygen quenching of electroluminescence. The sensor was fabricated as an organic light-emitting device (OLED) with phosphorescent dyes whose phosphorescence can be quenched by oxygen molecules, and with a polymer electrode which permeates oxygen molecules. The sensor was a single-layer OLED with Platinum (II) octaethylporphine (PtOEP) doped into poly(vinylcarbazole) (PVK) as an oxygen sensitive emissive layer and poly(3,4-ethylenedioxythiophene) mixed with poly(styrenesulfonate) (PEDOT:PSS) as an oxygen permeating polymer anode. The pressure sensitivity of the fabricated ELPS sample was equivalent to that of the sensor excited by an illumination light source. Moreover, the pressure sensitivity of the sensor is equivalent to that of conventional pressure-sensitive paint (PSP), which is an optical pressure sensor based on photoluminescence.

Efficient nondoped blue organic light-emitting diodes based on phenanthroimidazole-substituted anthracene derivatives

A series of new blue materials based on highly fluorescent di(aryl)anthracene and electron-transporting phenanthroimidazole functional cores: 2-(4-(anthracen-9-yl)phenyl)-1-phenyl-1H-phenanthro[9,10-d]imidazole (ACPI), 2-(4-(10-(naphthalen-1-yl)anthracen-9-yl)phenyl)-1-p-henyl-1H-phenanthro[9,10-d]imidazole (1-NaCPI), 2-(4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl)-1-phenyl-1H-phenanthro[9,10-d]imidazole (2-NaCPI) were designed and synthesized. These materials exhibit good film-forming and thermal properties as well as strong blue emission in the solid state. To explore the electroluminescence properties of these materials, three layer, two layer and single layer organic light-emitting devices were fabricated. With respect to the three layer device 4 using ACPI as the emitting layer, its maximum current efficiency reaches 4.36cdA−1 with Commission Internationale del’Eclairage (CIE) coordinates of (0.156, 0.155). In the single layer device 10 based on ACPI, maximum current efficiency reaches 1.59cdA−1 with Commission Internationale del’Eclairage (CIE) coordinates of (0.169, 0.177). Interestingly, both device 4 and 10 has low turn on voltage and negligible efficiency roll off at high current densities.

High-efficiency and low-efficiency-roll-off single-layer white organic light-emitting devices with a bipolar transport host

High-efficiency single-layer (SL) white organic light-emitting devices (WOLEDs) with a bipolar transport host were fabricated. The SL WOLEDs were achieved by combining blue and orange emission. Compared with the corresponding multilayer WOLEDs, the SL WOLEDs alleviated the efficiency roll-off without compromise of current efficiency due to the broader exciton formation zone and balance of carrier injection and transport. For example, The power efficiency of the SL WOLED based on Iridium (III) bis(4-phenylthieno[3,2-c]pyridinato-N,C2′) acetylacetonate orange emission could reach 20.9 lm/W at 1000 cd/m2, which also could reach 14.5 lm/W at a very high brightness of 5000 cd/m2.

Relating charge transport and performance in single-layer graded-composition organic light-emitting devices

Efficient electrophosphorescence is demonstrated using single-layer organic light-emitting devices (OLEDs) containing fac-tris(2-phenylpyridine) iridium (III) [Ir(ppy)3], bis(1-phenylisoquinoline)-(acetylacetonate) iridium (III) [PQIr], and iridium(III) bis[(4,6-difluorophenyl)-pyridinato-N,C2′]picolinate [FIrpic] for emission in the green, red, and blue, respectively. Peak forward-emitted external quantum (ηEQE) and power efficiencies (ηP) of ηEQE = (16.9 ± 0.4)% and ηP = (65.0 ± 1.1)lm/W, ηEQE = (12.0 ± 0.4)% and ηP = (8.3 ± 1.1) lm/W, and ηEQE = (10.9 ± 0.3)% and ηP = (28.1 ± 1.1)lm/W, are obtained for optimized green, red, and blue OLEDs, respectively. Devices are doped uniformly with the phosphorescent guest, and contain a continuously-varying host composition from predominately hole-transporting material (HTM) at the anode to predominately electron transporting material (ETM) at the cathode. The highly tunable composition gradient allows for the optimization of electron-hole charge balance and low-voltage operation while maintaining charge and exciton confinement. For each emitter, the optimum composition gradient is understood by considering the dependence of the electron and hole charge carrier mobilities on HTM:ETM composition.

Efficiency enhancement of solution‐processed single‐layer blue‐phosphorescence organic light‐emitting devices having co‐host materials of polymer (PVK) and small‐molecule (SimCP2)

Abstract— A new type of single‐layer blue‐phosphorescence organic light‐emitting devices (OLEDs) containing poly(9‐vinylcarbazole) (PVK) and small‐molecule‐based amorphous ambipolar bis(3,5‐di(9H‐carbazol‐9‐yl)phenyl) diphenylsilane (SimCP2) as the co‐host material have been demonstrated. All active materials [PVK, SimCP2, Flrpic (blue‐phosphorescence dopant), and OXD‐7 (electron transport)] were mixed in a single layer for solution processing in the fabrication of OLEDs. The SimCP2 small‐molecule host has adequate high electron and hole‐carrier mobiltieis of ∼10−4 cm2/V‐sec and a sufficiently large triplet state energy of ∼2.70 eV in confining emission energy on FIrpic. Based on such an architecture for single‐layer devices, a maximum external quantum efficiency of 6.2%, luminous efficiency of 15.8 cd/A, luminous power efficiency of 11 lm/W, and Commision Internale de l'Eclairage (CIEx,y) coordinates of (0.14,0.32) were achieved. Compared with those having PVK as the single‐host material, the improvement in the device performance is attributed to the balance of hole and electron mobilities of the co‐host material, efficient triplet‐state energy confinement on FIrpic, and the high homogeneity of the thin‐film active layer. Flexible blue‐phosphorescence OLEDs based on solution‐processed SimCP2 host material (withou PVK) have been demonstrated as well.

Solution processable single layer organic light-emitting devices with a single small molecular ionic iridium compound

We herein report on the occurrence of bright and efficient electrophosphorescence from a simple organic light-emitting diode (OLED) with a single organic layer comprised of a small molecular ionic iridium compound, formed using a solution process. The studied small molecular ionic iridium compound is [Ir(dfppy)2(bpy)]+PF6−, which exhibits excellent film-forming properties, bright green photoluminescence, and efficient bipolar carrier transport with balanced electron and hole mobilities of about 10−5 cm2/(V s). A high performance of the device was achieved by using a phosphorescent OLED (PHOLED) that was fabricated using the [Ir(dfppy)2(bpy)]+PF6− compound, with a peak brightness of about 18 000 cd/m2 and a peak current efficiency of 12 cd/A. A peak power efficiency of 2.5 lm/W was measured at 2800 cd/m2. These results suggest that the small molecular ionic iridium compound is a promising material for bright and efficient PHOLEDs manufactured using a simple solution process.

Highly efficient, single-layer organic light-emitting devices based on a graded-composition emissive layer

We demonstrate highly efficient electrophosphorescence from devices comprising a single organic layer. High efficiency is realized by combining both hole- and electron-transporting host materials (HTMs and ETMs, respectively) into a single, graded-composition emissive layer with the green phosphorescent emitter fac-tris(2-phenylpyridine) iridium (III). The composition is continuously graded to realize nearly 100% HTM at the anode and nearly 100% ETM at the cathode. Peak external quantum and power efficiencies of ηEQE=(19.3±0.4)% and ηP=(66.5±1.3) lm/W are realized at a luminance level of 600 cd/m2.

Non-doped Single-Layer Red-Emitting Electrofluorescent Devices Based on an Ambipolar Small Molecule

Non-doped red-emitting electrofluorescent single-layer organic light-emitting devices based on an ambipolar small molecule,4,9-bis(4-(2,2-diphenylvinyl)phenyl)naphtho[2,3-c][1,2,5] thiadiazole (BDPNTD),were studied.A WO3 or MoO3 buffer layer with an optimized thickness of 1 nm was used and the single-layer device has a low turn-on voltage (2.4 V) and a high luminance (4950 cd·m-2).The maximum emission wavelength was at about 636 nm and the CIE coordinates are at about (0.65,0.35).We confirmed that the WO3 or MoO3 buffer layer can improve hole injection at the ITO/BDPNTD interface and it creates a hole-electron balance in these devices.