Highly Efficient Green‐Emitting Phosphorescent Iridium Dendrimers Based on Carbazole Dendrons

Green‐emitting iridium dendrimers with rigid hole‐transporting carbazole dendrons are designed, synthesized, and investigated. With second‐generation dendrons, the photoluminescence quantum yield of the dendrimers is up to 87 % in solution and 45 % in a film. High‐quality films of the dendrimers are fabricated by spin‐coating, producing highly efficient, non‐doped electrophosphorescent organic light‐emitting diodes (OLEDs). With a device structure of indium tin oxide/poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonic acid)/neat dendrimer/1,3,5‐tris(2‐N‐phenylbenzimidazolyl)benzene/LiF/Al, a maximum external quantum efficiency (EQE) of 10.3 % and a maximum luminous efficiency of 34.7 cd A^–1 are realized. By doping the dendrimers into a carbazole‐based host, the maximum EQE can be further increased to 16.6 %. The integration of rigid hole‐transporting dendrons and phosphorescent complexes provides a new route to design highly efficient solution‐processable dendrimers for OLED applications.     

High‐Efficiency Red Phosphorescent Iridium Dendrimers with Charge‐ Transporting Dendrons: Synthesis and Electroluminescent Properties

A series of 1‐phenylisoquinoline derivatives encapsulated with peripheral arylamines as dendrons are synthesized by using the Ullmann reaction and palladium‐catalyzed aromatic carbon–carbon Suzuki‐coupling reactions. Red‐emitting dendritic iridium complexes (called G1‐1 , G1‐2 , and G2 ) are synthesized using the following derivatives: N,N‐diphenyl‐3′‐isoquinolin‐4‐biphenylaniline, N,N‐di(9,9‐dimethylfluorenyl‐3′‐isoquinolin‐4‐biphenylaniline, N,N‐di(4′‐di(2′‐(9′,9′‐dimethylfluorenyl)amine)biphenyl‐3′‐isoquinolin‐4‐biphenylaniline as the first ligands and 5‐methyl‐3‐(pyridin‐2′‐yl)‐1H‐1,2,4‐triazole as an ancillary ligand. The obtained dendrimers are soluble in common organic solvents, and uniform thin films can be spin‐coated from such solutions. Devices fabricated from dendritic iridium complexes G1‐2 and G2 with a small molecule host are fabricated by spin‐coating from chloroform solution in different device configurations. G1‐2 and G2 show similar device performances with maximum external quantum efficiencies (EQEs) of 12.8 % and 11.8 % (photons/electron) and luminous efficiency of 9.2 cd A^–1 and 8.5 cd A^–1 at 0.1 mA cm^–2, respectively. Devices based on polymer host poly(9,9‐dioctylfluorene)(PFO) (30 % PBD (2‐(4‐biphenyl)‐5‐(4‐tert‐butylphenyl‐1,3,4‐oxadiazole)) show a slightly higher efficiency for G1‐2 , with a maximum EQE of 13.9 % at a much higher current density of 6.4 mA cm^–2 and luminance of 601 cd m^–2.     

Toward Highly Efficient Solid‐State White Light‐Emitting Electrochemical Cells: Blue‐Green to Red Emitting Cationic Iridium Complexes with Imidazole‐Type Ancillary Ligands

Using imidazole‐type ancillary ligands, a new class of cationic iridium complexes ( 1 – 6 ) is prepared, and photophysical and electrochemical studies and theoretical calculations are performed. Compared with the widely used bpy (2,2′‐bipyridine)‐type ancillary ligands, imidazole‐type ancillary ligands can be prepared and modified with ease, and are capable of blueshifting the emission spectra of cationic iridium complexes. By tuning the conjugation length of the ancillary ligands, blue‐green to red emitting cationic iridium complexes are obtained. Single‐layer light‐emitting electrochemical cells (LECs) based on cationic iridium complexes show blue‐green to red electroluminescence. High efficiencies of 8.4, 18.6, and 13.2 cd A^?1 are achieved for the blue‐green‐emitting, yellow‐emitting, and orange‐emitting devices, respectively. By doping the red‐emitting complex into the blue‐green LEC, white LECs are realized, which give warm‐white light with Commission Internationale de L'Eclairage (CIE) coordinates of (0.42, 0.44) and color‐rendering indexes (CRI) of up to 81. The peak external quantum efficiency, current efficiency, and power efficiency of the white LECs reach 5.2%, 11.2 cd A^?1, and 10 lm W^?1, respectively, which are the highest for white LECs reported so far, and indicate the great potential for the use of these cationic iridium complexes in white LECs.     

Efficient Light‐Emitting Electrochemical Cells (LECs) Based on Ionic Iridium(III) Complexes with 1,3,4‐Oxadiazole Ligands

Eight new iridium(III) complexes 1‐8 , with 1,3,4‐oxadiazole (OXD) derivatives as the cyclometalated C^N ligand and/or the ancillary N^N ligands are synthesized and their electrochemical, photophysical, and solid‐state light‐emitting electrochemical cell (LEC) properties are investigated. Complexes 1 , 2 , 7 and 8 are additionally characterized by single crystal X‐ray diffraction. LECs based on complexes 1‐8 are fabricated with a structure indium tin oxide (ITO)/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/cationic iridium complex:ionic liquid/Al. LECs of complexes 1 – 6 with OXD derivatives as the cyclometalated ligands and as the ancillary ligand show yellow luminescence (λ_max = 552–564 nm). LECs of complexes 7 and 8 with cyclometalated C^N phenylpyridine ligands and an ancillary N^N OXD ligand show red emission (λ_max 616–624 nm). Using complex 7 external quantum efficiency (EQE) values of >10% are obtained for devices (210 nm emission layer) at 3.5 V. For thinner devices (70 nm) high brightness is achieved: red emission for 7 (8528 cd m^?2 at 10 V) and yellow emission for 1 (3125 cd m^?2 at 14 V).     

Solution‐Processible Carbazole Dendrimers as Host Materials for Highly Efficient Phosphorescent Organic Light‐Emitting Diodes

A group of dendrimers with oligo‐carbazole dendrons appended at 4,4′‐ positions of biphenyl core are synthesized for use as host materials for solution‐processible phosphorescent organic light‐emitting diodes (PHOLEDs). In comparison with the traditional small molecular host 4,4′‐N,N′‐dicarbazolebiphenyl (CBP), the dendritic conformation affords these materials extra merits including amorphous nature with extremely high glass transition temperatures (ca. 376 °C) and solution‐processibility, but inherent the identical triplet energies (2.60–2.62 eV). In comparison with the widely‐used polymeric host polyvinylcarbazole (PVK), these dendrimers possess much higher HOMO levels (–5.61 to –5.42 eV) that facilitate efficient hole injection and are favorable for high power efficiency in OLEDs. The agreeable properties and the solution‐processibility of these dendrimers makes it possible to fabricate highly efficient PHOLEDs by spin coating with the dendimers as phosphorescent hosts. The green PHOLED containing Ir(ppy)₃ (Hppy = 2‐phenyl‐pyridine) dopant exhibits high peak efficiencies of 38.71 cd A^?1 and 15.69 lm W^?1, which far exceed those of the control device with the PVK host (27.70 cd A^?1 and 9.6 lm W^?1) and are among the best results for solution‐processed green PHOLEDs ever reported. The versatility of these dendrimer hosts can be spread to orange PHOLEDs and high efficiencies of 32.22 cd A^?1 and 20.23 lm W^?1 are obtained, among the best ever reported for solution‐processed orange PHOLEDs.     

Solution‐Processible Phosphorescent Blue Dendrimers Based on Biphenyl‐Dendrons and Fac‐tris(phenyltriazolyl)iridium(III) Cores

Solution‐processible saturated blue phosphorescence is an important goal for organic light‐emitting diodes (OLEDs). Fac‐tris(5‐aryltriazolyl)iridium(III) complexes can emit blue phosphorescence at room temperature. Mono‐ and doubly dendronized fac‐tris(1‐methyl‐5‐phenyl‐3‐n‐propyl‐1H‐[1,2,4]triazolyl)iridium(III) 1 and fac‐tris{1‐methyl‐5‐(4‐fluorophenyl)‐3‐n‐propyl‐1H‐[1,2,4]triazolyl}iridium(III) 4 with first generation biphenyl‐based dendrons were prepared. The dendrimers emitted blue light at room temperature and could be solution processed to form thin films. The doubly dendronized 3 had a film photoluminescence quantum yield of 67% and Commission Internationale de l'Eclairage (CIE) coordinates of (0.17, 0.33). OLEDs comprised of a neat film of dendrimer 3 and an electron transport layer achieved a brightness of 142 cd m^?2 at 3.8 V with an external quantum efficiency of 7.9%, and CIE coordinates of (0.18, 0.35). Attachment of the fluorine atom to the emissive core had the effect of moving the luminescence to shorter wavelengths but also quenched the luminescence of the mono‐ and doubly dendronized dendrimers.     

Control of Charge Transport in Iridium(III) Complex‐Cored Carbazole Dendrimers by Generation and Structural Modification

Here, the charge transporting properties of a family of highly phosphorescent iridium(III) complex‐cored carbazole dendrimers designed to have improved charge transport by incorporating carbazole units into the dendrons are studied. Firstly, the effect of the dendrimer generation and the role of dendron for materials with one dendron per ligand of the core are considered. It is shown, in contrast to previously reported light‐emitting dendrimers, that in this case the carbazolyl‐based dendrons have an active role in charge transport. Next, the effect on the charge transport of attaching two dendrons per ligand to the dendrimer core is explored. In this latter case, for the so called “double dendron” material a highly non‐dispersive charge transport behavior is observed, together with a time‐of‐flight mobility of the order of 10^?3 cm² V^?1 s^?1. Furthermore the lowest energetic disorder parameter (σ) ever reported for a solution‐processed conjugated organic material is found, σ < 20 meV.     

High‐Throughput Combinatorial Optimizations of Perovskite Light‐Emitting Diodes Based on All‐Vacuum Deposition

Light‐emitting diodes (LEDs) based on lead halide perovskites demonstrate outstanding optoelectronic properties and are strong competitors for display and lighting applications. While previous halide perovskite LEDs are mainly produced via solution processing, here an all‐vacuum processing method is employed to construct CsPbBr₃ LEDs because vacuum processing exhibits high reliability and easy integration with existing OLED facilities for mass production. The high‐throughput combinatorial strategies are further adopted to study perovskite composition, annealing temperature, and functional layer thickness, thus significantly speeding up the optimization process. The best rigid device shows a current efficiency (CE) of 4.8 cd A^?1 (EQE of 1.45%) at 2358 cd m^?2, and best flexible device shows a CE of 4.16 cd A^?1 (EQE of 1.37%) at 2012 cd m^?2 with good bending tolerance. Moreover, by choosing NiO_x as the hole‐injection layer, the CE is improved to 10.15 cd A^?1 and EQE is improved to a record of 3.26% for perovskite LEDs produced by vacuum deposition. The time efficient combinatorial approaches can also be applied to optimize other perovskite LEDs.     

Light‐Emitting Paper

A solution‐based fabrication of flexible and light‐weight light‐emitting devices on paper substrates is reported. Two different types of paper substrates are coated with a surface‐emitting light‐emitting electrochemical cell (LEC) device: a multilayer‐coated specialty paper with an intermediate surface roughness of 0.4 μm and a low‐end and low‐cost copy paper with a large surface roughness of 5 μm. The entire device fabrication is executed using a handheld airbrush, and it is notable that all of the constituent layers are deposited from solution under ambient air. The top‐emitting paper‐LECs are highly flexible, and display a uniform light emission with a luminance of 200 cd m^?2 at a current conversion efficacy of 1.4 cd A^?1.     

Highly Efficient Yellow Organic Light Emitting Diode with a Novel Wet‐ and Dry‐Process Feasible Iridium Complex Emitter

Yellow emission is crucial in RGBY display technology and in fabricating physiologically friendly, low color‐temperature lighting sources. Emitters with both wet‐ and dry‐process feasibility are highly desirable to fabricate, respectively, high‐quality devices via vapor deposition and cost‐effective, large‐area devices via roll‐to‐roll fabrication. Here, high‐efficiency organic light‐emitting diodes with a novel wet‐ and dry‐process feasible yellow‐emitting iridium complex, bis[5‐methyl‐7‐fluoro‐5H‐benzo(c)(1,5) naphthyridin‐6‐one]iridium (picolinate), are demonstrated. By spin coating, the device shows, at 1000 cd m^?2, an external quantum efficiency (EQE) of 18.5% with an efficacy of 52.3 lm W^?1, the highest among all reported yellow devices via wet‐process, while using vapor deposition, the EQE is 22.6% with a 75.1 lm W^?1 efficacy, the highest among all dry‐processed counterparts. The high efficiency may be attributed to the replacement of the hydrogen atom with a fluorine atom on a 2‐substitutional site in the emitter to prevent dense molecular packing‐caused self‐quenching and to reduce radiationless deactivation rates, leading to a high quantum yield (71%).     

Efficient Nondoped Blue Fluorescent Organic Light‐Emitting Diodes (OLEDs) with a High External Quantum Efficiency of 9.4% @ 1000 cd m−2 Based on Phenanthroimidazole−Anthracene Derivative

Organic light‐emitting diodes (OLEDs) can promise flexible, light weight, energy conservation, and many other advantages for next‐generation display and lighting applications. However, achieving efficient blue electroluminescence still remains a challenge. Though both phosphorescent and thermally activated delayed fluorescence materials can realize high‐efficiency via effective triplet utilization, they need to be doped into appropriate host materials and often suffer from certain degree of efficiency roll‐off. Therefore, developing efficient blue‐emitting materials suitable for nondoped device with little efficiency roll‐off is of great significance in terms of practical applications. Herein, a phenanthroimidazole?anthracene blue‐emitting material is reported that can attain high efficiency at high luminescence in nondoped OLEDs. The maximum external quantum efficiency (EQE) of nondoped device is 9.44% which is acquired at the luminescence of 1000 cd m^?2. The EQE is still as high as 8.09% even the luminescence reaches 10 000 cd m^?2. The maximum luminescence is ≈57 000 cd m^?2. The electroluminescence (EL) spectrum shows an emission peak of 470 nm and the Commission International de L'Eclairage (CIE) coordinates is (0.14, 0.19) at the voltage of 7 V. To the best of the knowledge, this is among the best results of nondoped blue EL devices.     

White Organic Light‐Emitting Diodes with Evenly Separated Red,Green, and Blue Colors for Efficiency/Color‐Rendition Trade‐Off Optimization

A novel yellowish‐green triplet emitter, bis(5‐(trifluoromethyl)‐2‐p‐tolylpyridine) (acetylacetonate)iridium(III) (1), was conveniently synthesized and used in the fabrication of both monochromatic and white organic light‐emitting diodes (WOLEDs). At the optimal doping concentration, monochromatic devices based on 1 exhibit a high efficiency of 63 cd A^?1 (16.3% and 36.6 lm W^?1) at a luminance of 100 cd m^?2. By combining 1 with a phosphorescent sky‐blue emitter, bis(3,5‐difluoro‐2‐(2‐pyridyl)phenyl)‐(2‐carboxypyridyl)iridium(III) (FIrPic), and a red emitter, bis(2‐benzo[b]thiophen‐2‐yl‐pyridine)(acetylacetonate)iridium(III) (Ir(btp)₂(acac)), the resulting electrophosphorescent WOLEDs show three evenly separated main peaks and give a high efficiency of 34.2 cd A^?1 (13.2% and 18.5 lm W^?1) at a luminance of 100 cd m^?2. When 1 is mixed with a deep‐blue fluorescent emitter, 4,4′‐bis(9‐ethyl‐3‐carbazovinylene)‐1,1′‐biphenyl (BCzVBi), and Ir(btp)₂(acac), the resulting hybrid WOLEDs demonstrate a high color‐rendering index of 91.2 and CIE coordinates of (0.32, 0.34). The efficient and highly color‐pure WOLEDs based on 1 with evenly separated red, green, blue peaks and a high color‐rendering index outperform those of the state‐of‐the‐art emitter, fac‐tris(2‐phenylpyridine)iridium(III) (Ir(ppy)₃), and are ideal candidates for display and lighting applications.     

Multifunctional Fluorene‐Based Oligomers with Novel Spiro‐Annulated Triarylamine: Efficient,Stable Deep‐Blue Electroluminescence,Good Hole Injection,and Transporting Materials with Very High Tg

A series of fluorene‐based oligomers with novel spiro‐annulated triarylamine structures, namely DFSTPA, TFSTPA, and TFSDTC, are synthesized by a Suzuki cross‐coupling reaction. The spiro‐configuration molecular structures lead to very high glass transition temperatures (197–253 °C) and weak intermolecular interactions, and consequently the structures retain good morphological stability and high fluorescence quantum efficiencies(0.69–0.98). This molecular design simultaneously solves the spectral stability problems and hole‐injection and transport issues for fluorene‐based blue‐light‐emitting materials. Simple double‐layer electroluminescence (EL) devices with a configuration of ITO/TFSTPA (device A) or TFSDTC (device B)/ TPBI/LiF/Al, where TFSTPA and TFSDTC serve as hole‐transporting blue‐light‐emitting materials, show a deep‐blue emission with a peak around 432 nm, and CIE coordinates of (0.17, 0.12) for TFSTPA and (0.16, 0.07) for TFSDTC, respectively, which are very close to the National Television System Committee (NTSC) standard for blue (0.15, 0.07). The maximum current efficiency/external quantum efficiencies are 1.63 cd A^?1/1.6% for device A and 1.91 cd A^?1/2.7% for device B, respectively. In addition, a device with the structure ITO/DFSTPA/Alq₃/LiF/Al, where DFSTPA acts as both the hole‐injection and ‐transporting material, is shown to achieve a good performance, with a maximum luminance of 14 047 cd m^?2, and a maximum current efficiency of 5.56 cd A^?1. These values are significantly higher than those of devices based on commonly usedN,N′‐di(1‐naphthyl)‐N,N′‐diphenyl‐[1,1′‐biphenyl]‐4,4′‐diamine (NPB) as the hole‐transporting layer (11 738 cd m^?2 and 3.97 cd A^?1) under identical device conditions.     

An Indolocarbazole‐Based Thermally Activated Delayed Fluorescence Host for Solution‐Processed Phosphorescent Tandem Organic Light‐Emitting Devices Exhibiting Extremely Small Efficiency Roll‐Off

The study reports the development of a solution‐processed phosphorescent tandem organic light‐emitting device (OLED) exhibiting extremely small efficiency roll‐off. The OLED comprises two light‐emitting units (LEUs) connected by an interconnecting unit and employs a thermally activated delayed fluorescence host material. One of the most difficult tasks in the fabrication of OLEDs is to form a multilayer structure without dissolving the underlayer during the coating of the upper layer. The developed host materials exhibit high tolerance to methanol. The upper‐layer adjacent to the light‐emitting layer consists of ZnO nanoparticles, which could be dispersed in methanol by improving the preparation method. This results in the successful fabrication of a solution‐processed phosphorescent tandem OLED comprising two LEUs. The maximum external quantum efficiency (EQE) of the tandem device is 22.8%, and the EQE is 21.9% even at a high luminance of 10 000 cd m^?2. The suppression of efficiency roll‐off is among the best of those previously reported. Moreover, the operational stability of the tandem device is much higher compared with single‐LEU devices.     

A Light‐Blue Phosphorescent Dendrimer for Efficient Solution‐Processed Light‐Emitting Diodes

We describe the preparation of a dendrimer that is solution‐processible and contains 2‐ethylhexyloxy surface groups, biphenyl‐based dendrons, and a fac‐tris[2‐(2,4‐difluorophenyl)pyridyl]iridium(III ) core. The homoleptic complex is highly luminescent and the color of emission is similar to the heteroleptic iridium(III ) complex, bis[2‐(2,4‐difluorophenyl)pyridyl]picolinate iridium(III ) (FIrpic). To avoid the change in emission color that would arise from attaching a conjugated dendron to the ligand, the conjugation between the dendron and the ligand is decoupled by separating them with an ethane linkage. Bilayer devices containing a light‐emitting layer comprised of a 30 wt.‐% blend of the dendrimer in 1,3‐bis(N‐carbazolyl)benzene (mCP) and a 1,3,5‐tris(2‐N‐phenylbenzimidazolyl)benzene electron‐transport layer have external quantum and power efficiencies, respectively, of 10.4 % and 11 lm W^–1 at 100 cd m^–2 and 6.4 V. These efficiencies are higher than those reported for more complex device structures prepared via evaporation that contain FIrpic blended with mCP as the emitting layer, showing the advantage of using a dendritic structure to control processing and intermolecular interactions. The external quantum efficiency of 10.4 % corresponds to the maximum achievable efficiency based on the photoluminescence quantum yield of the emissive film and the standard out‐coupling of light from the device.     

Solution‐Processible 2,2′‐Dimethyl‐biphenyl Cored Carbazole Dendrimers as Universal Hosts for Efficient Blue,Green, and Red Phosphorescent OLEDs

A series of solution‐processible 2,2′‐dimethyl‐biphenyl cored dendrimers, namely G1MP, G2MP, and G3MP, is designed and synthesized by tuning the generation of periphery carbazole dendron. The resulting dendrimers all show excellent solubility in common organic solvents, and their high‐quality thin films can be formed via spin‐coating with a root‐mean‐square roughness in the range of 0.38–0.54 nm. G3MP, which contains the third‐generation carbazole dendron, has the greatest potential among those made here as an ideal universal host for multicolored triplet emitters. G3MP exhibits good thermal stability, with a glass transition temperature of 368 °C, a triplet energy as high as 2.85 eV enough to prevent the loss of triplet excitons, and suitable HOMO/LUMO levels of –5.30/–2.11 eV to facilitate both hole and electron injection and transport. When using G3MP as the host, highly efficient deep‐blue, blue, green, and red phosphorescent organic light‐emitting diodes (PhOLEDs) are successfully demonstrated, revealing a maximum luminous efficiency up to 18.2, 28.2, 54.0, and 12.7 cd A^–1 with the corresponding Commission Internationale de L'Eclairage (CIE) coordinates of (0.15, 0.23), (0.15, 0.35), (0.38, 0.59), and (0.64, 0.34), respectively. The state‐of‐art performance indicates that dendritic hosts have a favorable prospect of applications in solution‐processed white PhOLEDs and full‐color displays.     

An Alternative Approach to Constructing Solution Processable Multifunctional Materials: Their Structure,Properties, and Application in High‐Performance Organic Light‐Emitting Diodes

A new series of full hydrocarbons, namely 4,4′‐(9,9′‐(1,3‐phenylene)bis(9H‐fluorene‐9,9‐diyl))bis(N,N‐diphenylaniline) (DTPAFB), N,N′‐(4,4′‐(9,9′‐(1,3‐phenylene)bis(9H‐fluorene‐9,9‐diyl))bis(4,1‐phenylene))bis(N‐phenylnaphthalen‐1‐amine) (DNPAFB), 1,3‐bis(9‐(4‐(9H‐carbazol‐9‐yl)phenyl)‐9H‐fluoren‐9‐yl)benzene, and 1,3‐bis(9‐(4‐(3,6‐di‐tert‐butyl‐9H‐carbazol‐9‐yl)phenyl)‐9H‐fluoren‐9‐yl)benzene, featuring a highly twisted tetrahedral conformation, are designed and synthesized. Organic light‐emitting diodes (OLEDs) comprising DNPAFB and DTPAFB as hole transporting layers and tris(quinolin‐8‐yloxy)aluminum as an emitter are made either by vacuum deposition or by solution processing, and show much higher maximum efficiencies than the commonly used N,N′‐di(naphthalen‐1‐yl)‐N,N′‐diphenylbiphenyl‐4,4′‐diamine device (3.6 cd A^?1) of 7.0 cd A^?1 and 6.9 cd A^?1, respectively. In addition, the solution processed blue phosphorescent OLEDs employing the synthesized materials as hosts and iridium (III) bis[(4,6‐di‐fluorophenyl)‐pyridinato‐N, C²] picolinate (FIrpic) phosphor as an emitter present exciting results. For example, the DTPAFB device exhibits a brightness of 47 902 cd m^?2, a maximum luminescent efficiency of 24.3 cd A^?1, and a power efficiency of 13.0 lm W^?1. These results show that the devices are among the best solution processable blue phosphorescent OLEDs based on small molecules. Moreover, a new approach to constructing solution processable small molecules is proposed based on rigid and bulky fluorene and carbazole moieties combined in a highly twisted configuration, resulting in excellent solubility as well as chemical miscibility, without the need to introduce any solubilizing group such as an alkyl or alkoxy chain.     

A Novel Fluorene‐Triphenylamine Hybrid That is a Highly Efficient Host Material for Blue‐, Green‐, and Red‐Light‐Emitting Electrophosphorescent Devices

TFTPA (tris[4‐(9‐phenylfluoren‐9‐yl)phenyl]amine), a novel host material that contains a triphenylamine core and three 9‐phenyl‐9‐fluorenyl peripheries, was effectively synthesized through a Friedel‐Crafts‐type substitution reaction. Owing to the presence of its sterically bulky 9‐phenyl‐9‐fluorenyl groups, TFTPA exhibits a high glass transition temperature (186 °C) and is morphologically and electrochemically stable. In addition, as demonstrated from atomic force microscopy measurements, the aggregation of the triplet iridium dopant is significantly diminished in the TFTPA host, resulting in a highly efficient full‐color phosphorescence. The performance of TFTPA ‐based devices is far superior to those of the corresponding mCP‐ or CBP‐based devices, particularly in blue‐ and red‐emitting electrophosphorescent device systems. The efficiency of the FIrpic‐based blue‐emitting device reached 12 % (26 cd A^–1) and 18 lm W^–1 at a practical brightness of 100 cd m^–2; the Ir(piq)₂acac‐based red‐emitting device exhibited an extremely low turn‐on voltage (2.6 V) and a threefold enhancement in device efficiency (9.0 lm W^–1) relative to those of reference devices based on the CBP host material.     

Over 100 cd A−1 Efficient Quantum Dot Light‐Emitting Diodes with Inverted Tandem Structure

Quantum dot light‐emitting diodes (QLEDs) with tandem structure are promising candidates for future displays because of their advantages of pure emission color, long lifetime, high brightness, and high efficiency. To obtain efficient QLEDs, a solution‐processable interconnecting layer (ICL) based on poly(3, 4‐ethylenedioxythiophene)/polystyrene sulfonate/ZnMgO is developed. With the proposed ICL, all‐solution‐processed, inverted, tandem QLEDs are demonstrated with high current efficiency (CE) of 57.06 cd A^?1 and external quantum efficiency (EQE) of 13.65%. By further optimizing the fabrication processes and using a hybrid deposition technique, the resultant tandem QLEDs exhibit a very high CE over 100 cd A^?1 and an impressive EQE over 23%, which are the highest values ever reported and are comparable with those of the state‐of‐the‐art phosphorescent organic LEDs. Moreover, the efficiency roll‐off, a notorious phenomenon in phosphorescent LEDs, is significantly reduced in the developed QLEDs. For example, even at a very high brightness over 200 000 cd m^?2, the tandem QLEDs can still maintain a high CE of 96.47 cd A^?1 and an EQE of 22.62%. The proposed ICL and the developed fabrication methods allow for realization of very efficient tandem QLEDs for next generation display and lighting applications.     

Efficient Light‐Emitting Devices Based on Phosphorescent Polyhedral Oligomeric Silsesquioxane Materials

Synthesis, photophysical, and electrochemical characterizations of iridium‐complex anchored polyhedral oligomeric silsesquioxane (POSS) macromolecules are reported. Monochromatic organic light‐emitting devices based on these phosphorescent POSS materials show peak external quantum efficiencies in the range of 5–9%, which can be driven at a voltage less than 10 V for a luminance of 1000 cd m^?2. The white‐emitting devices with POSS emitters show an external quantum efficiency of 8%, a power efficiency of 8.1 lm W^?1, and Commission International de'lÉclairage coordinates of (0.36, 0.39) at 1000 cd m^?2. Encouraging efficiency is achieved in the devices based on hole‐transporting and Ir‐complex moieties dual‐functionalized POSS materials without using host materials, demonstrating that triplet‐dye and carrier‐transporting moieties functionalized POSS material is a viable approach for the development of solution‐processable electrophosphorescent devices.