New Solution‐Processable Electron Transport Materials for Highly Efficient Blue Phosphorescent OLEDs

Several new solution‐processable organic semiconductors based on dendritic oligoquinolines were synthesized and were used as electron‐transport and hole‐blocking materials to realize highly efficient blue phosphorescent organic light‐emitting diodes (PhOLEDs). Various substitutions on the quinoline rings while keeping the central meta‐linked tris(quinolin‐2‐yl)benzene gave electron transport materials that combined wide energy gap (>3.3 eV), moderate electron affinity (2.55‐2.8 eV), and deep HOMO energy level (<‐6.08 eV) with electron mobility as high as 3.3 × 10^?3 cm² V^?1 s^?1. Polymer‐based PhOLEDs with iridium (III) bis(4,6‐(di‐fluorophenyl)pyridinato‐N,C^2′)picolinate (FIrpic) blue triplet emitter and solution‐processed oligoquinolines as the electron‐transport layers (ETLs) gave luminous efficiency of 30.5 cd A^?1 at a brightness of 4130 cd m^?2 with an external quantum efficiency (EQE) of 16.0%. Blue PhOLEDs incorporating solution‐deposited ETLs were over two‐fold more efficient than those containing vacuum‐deposited ETLs. Atomic force microscopy imaging shows that the solution‐deposited oligoquinoline ETLs formed vertically oriented nanopillars and rough surfaces that enable good ETL/cathode contacts, eliminating the need for cathode interfacial materials (LiF, CsF). These solution‐processed blue PhOLEDs have the highest performance observed to date in polymer‐based blue PhOLEDs.     

A Bipolar Host Material Containing Triphenylamine and Diphenylphosphoryl‐Substituted Fluorene Units for Highly Efficient Blue Electrophosphorescence

Highly efficient blue electrophosphorescent organic light‐emitting diodes incorporating a bipolar host, 2,7‐bis(diphenylphosphoryl)‐9‐[4‐(N,N‐diphenylamino)phenyl]‐9‐phenylfluorene (POAPF), doped with a conventional blue triplet emitter, iridium(III) bis[(4,6‐difluoro‐phenyl)pyridinato‐N,C^2´]picolinate (FIrpic) are fabricated. The molecular architecture of POAPF features an electron‐donating (p‐type) triphenylamine group and an electron‐accepting (n‐type) 2,7‐bis(diphenyl‐phosphoryl)fluorene segment linked through the sp³‐hybridized C9 position of the fluorene unit. The lack of conjugation between these p‐ and n‐type groups endows POAPF with a triplet energy gap (E_T) of 2.75 eV, which is sufficiently high to confine the triplet excitons on the blue‐emitting guest. In addition, the built‐in bipolar functionality facilitates both electron and hole injection. As a result, a POAPF‐based device doped with 7 wt% FIrpic exhibits a very low turn‐on voltage (2.5 V) and high electroluminescence efficiencies (20.6% and 36.7 lm W^?1). Even at the practical brightnesses of 100 and 1000 cd m^?2, the efficiencies remain high (20.2%/33.8 lm W^?1 and 18.8%/24.3 lm W^?1, respectively), making POAPF a promising material for use in low‐power‐consumption devices for next‐generation flat‐panel displays and light sources.     

Solution‐Processed,Alkali Metal‐Salt‐Doped,Electron‐Transport Layers for High‐Performance Phosphorescent Organic Light‐Emitting Diodes

High‐performance, blue, phosphorescent organic light‐emitting diodes (PhOLEDs) are achieved by orthogonal solution‐processing of small‐molecule electron‐transport material doped with an alkali metal salt, including cesium carbonate (Cs₂CO₃) or lithium carbonate (Li₂CO₃). Blue PhOLEDs with solution‐processed 4,7‐diphenyl‐1,10‐phenanthroline (BPhen) electron‐transport layer (ETL) doped with Cs₂CO₃ show a luminous efficiency (LE) of 35.1 cd A^?1 with an external quantum efficiency (EQE) of 17.9%, which are two‐fold higher efficiency than a BPhen ETL without a dopant. These solution‐processed blue PhOLEDs are much superior compared to devices with vacuum‐deposited BPhen ETL/alkali metal salt cathode interfacial layer. Blue PhOLEDs with solution‐processed 1,3,5‐tris(m‐pyrid‐3‐yl‐phenyl)benzene (TmPyPB) ETL doped with Cs₂CO₃ have a luminous efficiency of 37.7 cd A^?1 with an EQE of 19.0%, which is the best performance observed to date in all‐solution‐processed blue PhOLEDs. The results show that a small‐molecule ETL doped with alkali metal salt can be realized by solution‐processing to enhance overall device performance. The solution‐processed metal salt‐doped ETLs exhibit a unique rough surface morphology that facilitates enhanced charge‐injection and transport in the devices. These results demonstrate that orthogonal solution‐processing of metal salt‐doped electron‐transport materials is a promising strategy for applications in various solution‐processed multilayered organic electronic devices.     

Nanodot‐Enhanced High‐Efficiency Pure‐White Organic Light‐Emitting Diodes with Mixed‐Host Structures

A relatively high‐efficiency, fluorescent pure‐white organic light‐emitting diode was fabricated using a polysilicic acid (PSA) nanodot‐embedded polymeric hole‐transporting layer (HTL). The diode employed a mixed host in the single emissive layer, which comprised 0.5 wt % yellow 5,6,11,12‐tetra‐phenylnaphthacene doped in the mixed host of 50 % 2‐(N,N‐diphenyl‐amino)‐6‐[4‐(N,N‐diphenylamino)styryl]naphthalene and 50 % N,N′‐bis‐(1‐naphthyl)‐N,N′‐diphenyl‐1,10‐biphenyl‐4‐4′‐diamine. By incorporating 7 wt % 3 nm PSA nanodot into the HTL of poly(3,4‐ethylene‐dioxythiophene)‐poly‐(styrenesulfonate), the efficiency at 100 cd m^–2 was increased from 13.5 lm W^–1 (14.7 cd A^–1; EQE: 7.2 %) to 17.1 lm W^–1 (17.6 cd A^–1; EQE: 8.3 %). The marked efficiency improvement may be attributed to the introduction of the PSA nanodot, leading to a better carrier‐injection‐balance.     

Bipolar Tetraarylsilanes as Universal Hosts for Blue,Green, Orange,and White Electrophosphorescence with High Efficiency and Low Efficiency Roll‐Off

A series of tetraarylsilane compounds, namely p‐BISiTPA ( 1 ), m‐BISiTPA ( 2 ), p‐OXDSiTPA ( 3 ), m‐OXDSiTPA ( 4 ), are designed and synthesized by incorporating electron‐donating arylamine and electron‐accepting benzimidazole or oxadiazole into one molecule via a silicon‐bridge linkage mode. Their thermal, photophysical and electrochemical properties can be finely tuned through the different groups and linking topologies. The para‐disposition compounds 1 and 3 display higher glass transition temperatures, slightly lower HOMO levels and triplet energies than their meta‐disposition isomers 2 and 4 , respectively. The silicon‐interrupted conjugation of the electron‐donating and electron‐accepting segments gives these materials the following advantages: i) relative high triplet energies in the range of 2.69–2.73 eV; ii) HOMO/LUMO levels of the compounds mainly depend on the electron‐donating and electron‐accepting groups, respectively; iii) bipolar transporting feature as indicated by hole‐only and electron‐only devices. These advantages make these materials ideal universal hosts for multicolor phosphorescent OLEDs. 1 and 3 have been demonstrated as universal hosts for blue, green, orange and white electrophosphorescence, exhibiting high efficiencies and low efficiency roll‐off. For example, the devices hosted by 1 achieve maximum external quantum efficiencies of 16.1% for blue, 22.7% for green, 20.5% for orange, and 19.1% for white electrophosphorescence. Furthermore, the external quantum efficiencies are still as high as 14.2% for blue, 22.4% for green, 18.9% for orange, and 17.4% for white electrophosphorescence at a high luminance of 1000 cd m^?2. The two‐color, all‐phosphor white device hosted by 3 acquires a maximum current efficiency of 51.4 cd A^?1, and a maximum power efficiency of 51.9 lm W^?1. These values are among the highest for single emitting layer white PhOLEDs reported till now.     

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.     

Significance of irreversible formation of “electromer” in 1-bis[4-[N,N-di(4-tolyl)amino]phenyl]-cyclohexane layer associated with the stability of deep blue phosphorescent organic light emitting diodes

We demonstrate that injection of electrons in 1-bis[4-[N,N-di(4-tolyl)amino]phenyl]-cyclohexane (TAPC) layer irreversibly induces defect sites responsible for “electromer” emission. We also show that the defects alter the charge transporting properties of TAPC layer to influence the charge balance of iridium(III)[bis(4,6-difluorophenyl)pyridinato-N,C^2′]tetrakis(1-pyrazolyl)borate (FIr6) based deep blue phosphorescent organic light emitting diodes (PHOLED). The present investigation implies that deep-blue PHOLEDs should be carefully designed for the emission zone to be located far enough from the TAPC layer so as to avoid or minimize the emission from TAPC layer.     

Molecular design of large-bandgap host materials and their application to blue phosphorescent organic light-emitting diodes

New large-bandgap host materials with carbazole and carboline moieties were designed and synthesized for high-performance blue phosphorescent organic light-emitting diodes (PhOLEDs). The two kinds of host materials, 9-(4-(9H-carbazol-9-yl)phenyl)-6-(9H-carbazol-9-yl)-9H-pyrido[2,3-b]indole (pP2CZCB) and 9-(3-(9H-carbazol-9-yl)phenyl)-6-(9H-carbazol-9-yl)-9H-pyrido[2,3-b]indole (mP2CZCB), displayed promisingly high triplet energies of ∼2.92–2.93 eV for enhancing the exothermic energy transfer to bis[2-(4,6-difluorophenyl)pyridinato-C²,N](picolinato)iridium(III) (FIrpic) in PhOLED devices. It was found that the blue PhOLEDs bearing the new host materials and the FIrpic dopant exhibited markedly higher external quantum efficiencies (EQEs) than a device made with 1,3-bis(N-carbazolyl)benzene (mCP) as the host. In particular, the PhOLED device made with 3 wt% FIrpic as the dopant and mP2CZCB as the host material displayed a low driving voltage of 4.13 V and the high EQE of 25.3% at 1000 cd m⁻².     

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.     

Structure–Property Relationship of Pyridine‐Containing Triphenyl Benzene Electron‐Transport Materials for Highly Efficient Blue Phosphorescent OLEDs

Three triphenyl benzene derivatives of 1,3,5‐tri(m‐pyrid‐2‐yl‐phenyl)benzene (Tm2PyPB), 1,3,5‐tri(m‐pyrid‐3‐yl‐phenyl)benzene (Tm3PyPB) and 1,3,5‐tri(m‐pyrid‐4‐yl‐phenyl)benzene (Tm4PyPB), containing pyridine rings at the periphery, are developed as electron‐transport and hole/exciton‐blocking materials for iridium(III) bis(4,6‐(di‐fluorophenyl)pyridinato‐N,C^2′)picolinate (FIrpic)‐based blue phosphorescent organic light‐emitting devices. Their highest occupied molecular orbital and lowest unoccupied molecular orbital (LUMO) energy levels decrease as the nitrogen atom of the pyridine ring moves from position 2 to 3 and 4; this is supported by both experimental results and density functional theory calculations, and gives improved electron‐injection and hole‐blocking properties. They exhibit a high electron mobility of 10^?4–10^?3 cm² V^?1 s^?1 and a high triplet energy level of 2.75 eV. Confinement of FIrpic triplet excitons is strongly dependent on the nitrogen atom position of the pyridine ring. The second exponential decay component in the transient photoluminescence decays of Firpic‐doped films also decreases when the position of the nitrogen atom in the pyridine ring changes. Reduced driving voltages are obtained when the nitrogen atom position changes because of improved electron injection as a result of the reduced LUMO level, but a better carrier balance is achieved for the Tm3PyPB‐based device. An external quantum efficiency (EQE) over 93% of maximum EQE was achieved for the Tm4PyPB‐based device at an illumination‐relevant luminance of 1000 cd m^?2, indicating reduced efficiency roll‐off due to better confinement of FIrpic triplet excitons by Tm4PyPB in contrast to Tm2PyPB and Tm3PyPB.     

An Exciplex Forming Host for Highly Efficient Blue Organic Light Emitting Diodes with Low Driving Voltage

The exciplex forming co‐host with phosphorescent dopant system has potential to realize highly efficient phosphorescent organic light emitting didoes (PhOLEDs). However, the exciplex forming co‐host for blue phosphorescent OLEDs has been rarely introduced because of higher triplet level of the blue dopant than green and red dopants. In this work, a novel exciplex forming co‐host with high triplet energy level is developed by mixing a phosphine oxide based electron transporting material, PO‐T2T, and a hole transporting material, N,N′‐dicarbazolyl‐3,5‐benzene (mCP). Photo‐physical analysis shows that the exciplexes are formed efficiently in the host and the energy transfer from the exciplex to blue phosphorescent dopant (iridium(III)bis[(4,6‐difluorophenyl)‐pyridinato‐N,C2′]picolinate; FIrpic) is also efficient, enabling the triplet harvest without energy loss. As a result, an unprecedented high performance blue PhOLED with the exciplex forming co‐host is demonstrated, showing a maximum external quantum efficiency (EQE) of 30.3%, a maximum power efficiency of 66 lm W^?1, and low driving voltage of 2.75 at 100 cd m^?2, 3.29 V at 1000 cd m^?2, and 4.65 V at 10 000 cd m^?2, respectively. The importance of the exciton confinement in the exciplex forming co‐host is further investigated which is directly related to the performance of PhOLEDs.     

A Highly Efficient Host/Dopant Combination for Blue Organic Electrophosphorescence Devices

We have synthesized a new blue‐emitting iridium complex, FIrpytz (iridium(III) bis(4,6‐difluorophenylpyridinato)‐4‐(pyridin‐2‐yl)‐1,2,3‐triazolate), and two new bis(triphenylsilyl) derivatives, BSB (4,4'‐bis‐triphenylsilanyl‐biphenyl) and BST (4,4″‐bis(triphenylsilanyl)‐(1,1′,4′,1″)‐terphenyl) as hosts for blue phosphorescence devices. The photoluminescence (PL) and electroluminescence (EL) properties of different host/dopant combinations were studied in details. These two arylsilanes showed glass transition temperatures (T_gs) ≥ 100 °C higher than those of UGH1 (diphenyl‐di(o‐tolyl)silane) and UGH2 (1,4‐bis(triphenylsilyl)benzene), the common arylsilane‐based hosts. The band gaps for BSB and BST are 4.16 and 3.78 eV, respectively, lower than that of UGH2 of 4.40 eV. The FIrpytz‐doped UGH2, BSB and BST films exhibit PL quantum yields of 0.58, 0.83 and 0.48, respectively. The EL devices using FIrpytz or FIrpic (iridium(III) bis(4,6‐difluorophenylpyridinato)‐picolinate) as the blue phosphorescence dopants and UGH2, BSB and BST as the hosts also showed that BSB‐based devices gave the best device efficiencies. Both PL and EL studies show that BSB is better than UGH2 and BST as the host material for FIrpytz and FIrpic. In particular, the use of FIrpytz as dopant, BSB as host and LiF/Al as cathode provides a remarkably efficient combination for blue electrophosphorescence device reaching a very high external quantum efficiency of 19.3% at 8.5 V and a high luminance level of 20500 cd m⁻² at 19.3 V after electroluminescence started at 5.1 V.     

Red Phosphorescent Iridium Complex Containing Carbazole‐Functionalized β‐Diketonate for Highly Efficient Nondoped Organic Light‐Emitting Diodes

A novel red phosphorescent iridium complex containing a carbazole‐functionalized β‐diketonate, Ir(DBQ)₂(CBDK) (bis(dibenzo[f,h]quinoxalinato‐N,C²) iridium (1‐(carbazol‐9‐yl)‐5,5‐dimethylhexane‐2,4‐diketonate)) is designed, synthesized, and characterized. The electrophosphorescence properties of a nondoped device using the title complex as an emitter with a device configuration of indium tin oxide (ITO)/N,N′‐diphenyl‐N,N′‐bis(1‐naphthyl)‐1,1′‐diphenyl‐4,4′‐diamine (NPB; 20 nm)/iridium complex (20 nm)/2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline (BCP; 5 nm)/tris(8‐hydroxyquinoline) (AlQ; 30 nm)/Mg_0.9Ag_0.1 (200 nm)/Ag (80 nm) are examined. The results show that the nondoped device achieves a maximum lumen efficiency as high as 3.49 lm W^–1. To understand this excellent result observed, two reference complexes Ir(DBQ)₂(acac), where acac is the acetyl acetonate anion, and Ir(DBQ)₂(FBDK), [bis(dibenzo[f,h]quinoxalinato‐N,C²) iridium (1‐(9‐methyl‐fluoren‐9‐yl)‐6,6‐dimethylheptane‐3,5‐diketonate)], have also been synthesized, and as emitters they were examined under the same device configuration. The maximum lumen efficiency of the former compound is found to be 0.26 lm W^–1 while that for the latter is 0.37 lm W^–1, suggesting that the excellent performance of Ir(DBQ)₂(CBDK) can be attributed mainly to an improved hole‐transporting property that benefits the exciton transport. In addition, a bulky diketonate group separates the emitter centers from each other, which is also important for organic light‐emitting diodes.     

Highly Efficient Electron‐Transporting/Injecting and Thermally Stable Naphthyridines for Organic Electrophosphorescent Devices

A series of 1,8‐naphthyridine derivatives is synthesized and their electron‐transporting/injecting (ET/EI) properties are investigated via a multilayered electrophosphorescent organic light‐emitting device (OLED) using fac‐tris(2‐phenylpyridine)iridium [Ir(ppy)₃] as a green phosphorescent emitter doped into a 4,4′‐N,N′‐dicarbazolebiphenyl (CBP) host with 4,4′‐bis[N‐(1‐naphthyl)‐N‐phenylamino]biphenyl (a‐NPD) as the hole‐transporting layer, and poly(arylene ether sulfone) containing tetraphenylbenzidine (TPDPES) doped with tris(4‐bromophenyl)ammonium hexachloroantimonate (TBPAH) as the hole‐injecting layer. The turn‐on voltage of the device is 2.5 V using 2,7‐bis[3‐(2‐phenyl)‐1,8‐naphthyridinyl]‐9,9‐dimethylfluorene (DNPF), lower than that of 3.0 V for the device using a conventional ET material. The maximum current efficiency (CE) and power efficiency (PE) of the DNPF device are much higher than those of a conventional device. With the aid of a hole‐blocking (HB) and exciton‐blocking layer of bathocuproine (BCP), 13.2–13.7% of the maximum external quantum efficiency (EQE) and a maximum PE of 50.2–54.5 lm W^?1 are obtained using the naphthyridine derivatives; these values are comparable with or even higher than the 13.6% for conventional ET material. The naphthyridine derivatives show high thermal stabilities, glass‐transition temperatures much higher than that of aluminum(III) bis(2‐methyl‐8‐quinolinato)‐4‐phenylphenolate (BAlq), and decomposition temperatures of 510–518 °C, comparable to or even higher than those of Alq₃.     

Dependence of Light‐Emitting Characteristics of Blue Phosphorescent Organic Light‐Emitting Diodes on Electron Injection and Transport Materials

We investigate the light‐emitting performances of blue phosphorescent organic light‐emitting diodes (PHOLEDs) with three different electron injection and transport materials, that is, bathocuproine(2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline) (Bphen), 1,3,5‐tri(m‐pyrid‐3‐yl‐phenyl)benzene (Tm3PyPB), and 2,6‐bis(3‐(carbazol‐9‐yl)phenyl)pyridine (26DCzPPy), which are partially doped with cesium metal. We find that the device characteristics are very dependent on the nature of the introduced electron injection layer (EIL) and electron transporting layer (ETL). When the appropriate EIL and ETL are combined, the peak external quantum efficiency and peak power efficiency improve up to 20.7% and 45.6 lm/W, respectively. Moreover, this blue PHOLED even maintains high external quantum efficiency of 19.6% and 16.9% at a luminance of 1,000 cd/m² and 10,000 cd/m², respectively.     

Molecular Engineering of Host Materials for High‐Performance Phosphorescent OLEDs: Zig‐Zag Conformation with 3D Gridding Packing Mode Facilitating Charge Balance and Quench Suppression

A group of bipyridine/carbazole hybrid compounds, namely m‐BPyDCz, p‐BPyDCz, m‐BPySCz, and p‐BPySCz, are designed and developed as host materials for phosphorescent organic light‐emitting diodes (PhOLEDs). By tuning the p/n molar ratio and para‐/meta‐ substitution style, scorpion‐, Y‐, Z‐, and L‐shape molecular conformations are generated. In virtue of intermolecular hydrogen bonds and π–π interaction, these compounds form different molecular packing patterns in their single crystals. Particularly the Z‐shaped m‐BPySCz achieves 3D gridding packing with regular and ordered carbazole and pyridine columns as carrier hoping channels and larger intermolecular distance, which not only guarantees charge balance but also suppresses exciton quenching. Consequently the m‐BPySCz hosted sky‐blue and green PhOLEDs exhibit high external quantum efficiencies of 27.3% and 28.0% and low efficiency roll‐offs of 8.1% (at brightness of 1000 cd m^?2 for blue) and 14.3% (at 10000 cd m^?2 for green), all superior to other analogs and many reported host materials. The excellent performance of m‐BPySCz versus its lowest molecular weight and lowest amorphous stability manifests that the molecular packing style of host material dominates to determine the overall performance of PhOLEDs and the 3D gridding packing mode of zig‐zag conformation may be one ideal strategy to eliminate efficiency roll‐off in PhOLEDs.     

Multifunctional Deep‐Blue Emitter Comprising an Anthracene Core and Terminal Triphenylphosphine Oxide Groups

A highly efficient blue‐light emitter, 2‐tert‐butyl‐9,10‐bis[4′‐(diphenyl‐phosphoryl)phenyl]anthracene (POAn) is synthesized, and comprises electron‐deficient triphenylphosphine oxide side groups appended to the 9‐ and 10‐positions of a 2‐tert‐butylanthracene core. This sophisticated anthracene compound possesses a non‐coplanar configuration that results in a decreased tendency to crystallize and weaker intermolecular interactions in the solid state, leading to its pronounced morphological stability and high quantum efficiency. In addition to serving as an electron‐transporting blue‐light‐emitting material, POAn also facilitates electron injection from the Al cathode to itself. Consequently, simple double‐layer devices incorporating POAn as the emitting, electron‐transporting, and ‐injecting material produce bright deep‐blue lights having Commission Internationale de L'Eclairage coordinates of (0.15,0.07). The peak electroluminescence performance was 4.3% (2.9 cd A^?1). For a device lacking an electron‐transport layer or alkali fluoride, this device displays the best performance of any such the deep‐blue organic light‐emitting diodes reported to date.     

The Fabrication and Characterization of Single‐Component Polymeric White‐Light‐Emitting Diodes

By using Ni⁰‐mediated polymerization, we have systematically synthesized a series of fluorene‐based copolymers composed of blue‐, green‐, and red‐light‐emitting comonomers with a view to producing polymers with white‐light emission. 2,7‐Dibromo‐9,9‐dihexylfluorene, {4‐(2‐[2,5‐dibromo‐4‐{2‐(4‐diphenylamino‐phenyl)‐vinyl}‐phenyl]‐vinyl)‐phenyl}‐diphenylamine (DTPA), and 2‐{2‐(2‐[4‐{bis(4‐bromo‐phenyl)amino}‐phenyl]‐vinyl)‐6‐tert‐butyl‐pyran‐4‐ylidene}‐malononitrile (TPDCM) were used as the blue‐, green‐, and red‐light‐emitting comonomers, respectively. It was found that the emission spectra of the resulting copolymers could easily be tuned by varying their DTPA and TPDCM content. Thus with the appropriate red/green/blue (RGB) unit ratio, we were able to obtain white‐light emission from these copolymers. A white‐light‐emitting diode using the polyfluorene copolymer containing 3 % green‐emitting DTPA and 2 % red‐emitting TPDCM (PG3R2) with a structure of indium tin oxide/poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonic acid)/PG3R2/Ca/Al was found to exhibit a maximum brightness of 820 cd m^–2 at 11 V with Commission Internationale de L'Eclairage (CIE) coordinates of (0.33,0.35), which are close to the standard CIE coordinates for white‐light emission (0.33,0.33).     

Rational Design of Charge‐Neutral,Near‐Infrared‐Emitting Osmium(II) Complexes and OLED Fabrication

A new series of charge neutral Os(II) isoquinolyl triazolate complexes ( 1 – 4 ) with both trans and cis arrangement of phosphine donors are synthesized, and their structural, electrochemical and photophysical properties are established. In sharp contrast to the cis‐arranged complexes 2 – 4 , the trans derivative 1 , which shows a planar arrangement of chromophoric N‐substituted chelates, offers the most effective extended π‐delocalization and hence the lowest excited state energy gap. These complexes exhibit phosphorescence with peak wavelengths ranging from 692–805 nm in degassed CH₂Cl₂ at room temperature. Near‐infrared (NIR)‐emitting electroluminescent devices employing 6 wt % of 1 (or 4 ) doped in Alq₃ host material are successfully fabricated. The devices incorporating 1 as NIR phosphor exhibit fairly intense emission with a peak wavelength at 814 nm. Forward radiant emittance reaches as high as 65.02 µW cm^?2, and a peak EQE of ～1.5% with devices employing Alq₃, TPBi and/or TAZ as electron‐transporting/exciton‐blocking layers. Upon switching to phosphor 4 , the electroluminescence blue shifts to 718 nm, while the maximum EQE and radiance increase to 2.7% and 93.26 (μW cm^?2) respectively. Their performances are optimized upon using TAZ as the electron transporting and exciton‐blocking material. The OLEDs characterized represent the only NIR‐emitting devices fabricated using charge‐neutral and volatile Os(II) phosphors via thermal vacuum deposition.     

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.