Highly Efficient Non‐Doped Blue Organic Light‐Emitting Diodes Based on Fluorene Derivatives with High Thermal Stability

A new series of blue‐light‐emitting fluorene derivatives have been synthesized and characterized. The fluorene derivatives have high fluorescence yields, good thermal stability, and high glass‐transition temperatures in the range 145–193 °C. Organic light‐emitting diodes (OLEDs) fabricated using the fluorene derivatives as the host emitter show high efficiency (up to 5.3 cd A^–1 and 3.0 lm W^–1) and bright blue‐light emission (Commission Internationale de L'Eclairage (CIE) coordinates of x = 0.16, y = 0.22). The performance of the non‐doped fluorene‐based devices is among the best fluorescent blue‐light‐emitting OLEDs. The good performance of the present blue OLEDs is considered to derive from: 1) appropriate energy levels of the fluorene derivatives for good carrier injection; 2) good carrier‐transporting properties; and 3) high fluorescence efficiency of the fluorene derivatives. These merits are discussed in terms of the molecular structures.     

Molecular Engineering of Blue Fluorescent Molecules Based on Silicon End‐Capped Diphenylaminofluorene Derivatives for Efficient Organic Light‐Emitting Materials

Blue fluorescent materials based on silicone end‐capped 2‐diphenylaminofluorene derivatives are synthesized and characterized. These materials are doped into a 2‐methyl‐9,10‐di‐[2‐naphthyl]anthracene host as blue dopant materials in the emitting layer of organic light‐emitting diode devices bearing a structure of ITO/DNTPD (60 nm)/NPB (30 nm)/emitting layer (30 nm)/Alq₃ (20 nm)/LiF (1.0 nm)/Al (200 nm). All devices exhibit highly efficient blue electroluminescence with high external quantum efficiencies (3.47%–7.34% at 20 mA cm^?2). The best luminous efficiency of 11.2 cd A^?1 and highest quantum efficiency of 7.34% at 20 mA cm^?2 are obtained in a device with CIE coordinates (0.15, 0.25). A deep‐blue OLED with CIE coordinates (0.15, 0.14) exhibits a luminous efficiency of 3.70 cd A^?1 and quantum efficiency of 3.47% at 20 mA cm^?2.     

Blue‐Light‐Emitting Oligoquinolines: Synthesis,Properties, and High‐Efficiency Blue‐Light‐Emitting Diodes

The synthesis, photophysics, cyclic voltammetry, and highly efficient blue electroluminescence of a series of four new n‐type conjugated oligomers, 6,6′‐bis(2,4‐diphenylquinoline) (B1PPQ), 6,6′‐bis(2‐(4‐tert‐butylphenyl)‐4‐phenylquinoline) (BtBPQ), 6,6′‐bis(2‐p‐biphenyl)‐4‐phenylquinoline) (B2PPQ), and 6,6′‐bis((3,5‐diphenylbenzene)‐4‐phenylquinoline) (BDBPQ) is reported. The oligoquinolines have high glass‐transition temperatures (T_g ≥ 133 °C), reversible electrochemical reduction, and high electron affinities (2.68–2.81 eV). They emit blue photoluminescence with 0.73–0.94 quantum yields and 1.06–1.42 ns lifetimes in chloroform solutions. High‐performance organic light‐emitting diodes (OLEDs) with excellent blue chromaticity coordinates are achieved from all the oligoquinolines. OLEDs based on B2PPQ as the blue emitter give the best performance with a high brightness (19 740 cd m^–2 at 8.0 V), high efficiency (7.12 cd A^–1 and 6.56 % external quantum efficiency at 1175 cd m^–2), and excellent blue color purity as judged by the Commission Internationale de L'Eclairage (CIE) coordinates (x = 0.15,y = 0.16). These results represent the best efficiency of blue OLEDs from neat fluorescent organic emitters reported to date. These results demonstrate the potential of oligoquinolines as emitters and electron‐transport materials for developing high‐performance blue OLEDs.     

High‐Efficiency Deep‐Blue Light‐Emitting Diodes Based on Phenylquinoline/Carbazole‐Based Compounds

Highly efficient deep‐blue fluorescent materials based on phenylquinoline–carbazole derivatives (PhQ‐CVz, MeO‐PhQ‐CVz, and CN‐PhQ‐CVz) are synthesized for organic light‐emitting diodes (OLEDs). The materials form high‐quality amorphous thin films by thermal evaporation and the energy levels can be easily adjusted by the introduction of different electron‐donating and electron‐withdrawing groups on carbazoylphenylquinoline. Non‐doped deep‐blue OLEDs that use PhQ‐CVz as the emitter show bright emission (Commission Internationale de L'Éclairage (CIE) coordinates, x = 0.156, y = 0.093) with an external quantum efficiency of 2.45%. Furthermore, the material works as an excellent host material for 4,4′‐bis(9‐ethyl‐3‐carbazovinylene)‐1,1′‐biphenyl dopant to get high‐performance OLEDs with excellent deep‐blue CIE coordinates (x = 0.155, y = 0.157), high power efficiency (5.98 lm W^?1), and high external quantum efficiency (5.22%).     

High‐Purity‐Blue and High‐Efficiency Electroluminescent Devices Based on Anthracene

Novel blue‐light‐emitting materials, 9,10‐bis(1,2‐diphenyl styryl)anthracene (BDSA) and 9,10‐bis(4′‐triphenylsilylphenyl)anthracene (BTSA), which are composed of an anthracene molecule as the main unit and a rigid and bulky 1,2‐diphenylstyryl or triphenylsilylphenyl side unit, have been designed and synthesized. Theoretical calculations on the three‐dimensional structures of BDSA and BTSA show that they have a non‐coplanar structure and inhibited intermolecular interactions, resulting in a high luminescence efficiency and good color purity. By incorporating these new, non‐doped, blue‐light‐emitting materials into a multilayer device structure, it is possible to achieve luminance efficiencies of 1.43 lm W^–1 (3.0 cd A^–1 at 6.6 V) for BDSA and 0.61 lm W^–1 (1.3 cd A^–1 at 6.7 V) for BTSA at 10 mA cm^–2. The electroluminescence spectrum of the indium tin oxide (ITO)/copper phthalocyanine (CuPc)/1,4‐bis[(1‐naphthylphenyl)‐amino]biphenyl (α‐NPD)/BDSA/tris(9‐hydroxyquinolinato)aluminum (Alq₃)/LiF/Al device shows a narrow emission band with a full width at half maximum (FWHM) of 55 nm and a λ_max = 453 nm. The FWHM of the ITO/CuPc/α‐NPD/BTSA/Alq₃/LiF/Al device is 53 nm, with a λ_max = 436 nm. Regarding color, the devices showed highly pure blue emission ((x,y) = (0.15,0.09) for BTSA, (x,y) = (0.14,0.10) for BDSA) at 10 mA cm^–2 in Commission Internationale de l'Eclairage (CIE) chromaticity coordinates.     

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.     

Unexpected Propeller‐Like Hexakis(fluoren‐2‐yl)benzene Cores for Six‐Arm Star‐Shaped Oligofluorenes: Highly Efficient Deep‐Blue Fluorescent Emitters and Good Hole‐Transporting Materials

Grafting six fluorene units to a benzene ring generates a new highly twisted core of hexakis(fluoren‐2‐yl)benzene. Based on the new core, six‐arm star‐shaped oligofluorenes from the first generation T1 to third generation T3 are constructed. Their thermal, photophysical, and electrochemical properties are studied, and the relationship between the structures and properties is discussed. Simple double‐layer electroluminescence (EL) devices using T1–T3 as non‐doped solution‐processed emitters display deep‐blue emissions with Commission Internationale de l'Eclairage (CIE) coordinates of (0.17, 0.08) for T1 , (0.16, 0.08) for T2 , and (0.16, 0.07) for T3 . These devices exhibit excellent performance, with maximum current efficiency of up to 5.4 cd A^?1, and maximum external quantum efficiency of up to 6.8%, which is the highest efficiency for non‐doped solution‐processed deep‐blue organic light‐emitting diodes (OLEDs) based on starburst oligofluorenes, and is even comparable with other solution‐processed deep‐blue fluorescent OLEDs. Furthermore, T2‐ and T3‐ based devices show striking blue EL color stability independent of driving voltage. In addition, using T0–T3 as hole‐transporting materials, the devices of indium tin oxide (ITO)/poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS)/ T0–T3 /tris(8‐hydroxyquinolinato)aluminium (Alq₃)/LiF/Al achieve maximum current efficiencies of 5.51–6.62 cd A^?1, which are among the highest for hole‐transporting materials in identical device structure.     

Unexpected Sole Enol‐Form Emission of 2‐(2′‐Hydroxyphenyl)oxazoles for Highly Efficient Deep‐Blue‐Emitting Organic Electroluminescent Devices

Considerable efforts have been devoted to the development of highly efficient blue light‐emitting materials. However, deep‐blue fluorescence materials that can satisfy the Commission Internationale de l'Eclairage (CIE) coordinates of (0.14, 0.08) of the National Television System Committee (NTSC) standard blue and, moreover, possess a high external quantum efficiency (EQE) over 5%, remain scarce. Here, the unusual luminescence properties of triphenylamine‐bearing 2‐(2′‐hydroxyphenyl)oxazoles ( 3a–3c ) and their applications in organic light‐emitting diodes (OLEDs) are reported as highly efficient deep‐blue emitters. The 3a ‐based device exhibits a high spectral stability and an excellent color purity with a narrow full‐width at half‐maximum of 53 nm and the CIE coordinates of (0.15, 0.08), which is very close to the NTSC standard blue. The exciton utilization of the device closes to 100%, exceeding the theoretical limit of 25% in conventional fluorescent OLEDs. Experimental data and theoretical calculations demonstrate that 3a possesses a highly hybridized local and charge‐transfer excited state character. In OLEDs, 3a exhibits a maximum luminance of 9054 cd m^?2 and an EQE up to 7.1%, which is the first example of highly efficient blue OLEDs based on the sole enol‐form emission of 2‐(2′‐hydroxyphenyl)azoles.     

A DCM‐Type Red‐Fluorescent Dopant for High‐Performance Organic Electroluminescent Devices

2‐(2‐tert‐Butyl‐6‐((E)‐2‐(2,6,6‐trimethyl‐2,4,5,6‐tetrahydro‐1H‐pyrrolo[3,2,1‐ij]quinolin‐8‐yl)vinyl)‐4H‐pyran‐4‐ylidene)malononitrile (DCQTB) is designed and synthesized in high yield for application as the red‐light‐emitting dopant in organic light‐emitting diodes (OLEDs). Compared with 4‐(dicyanomethylene)‐2‐tert‐butyl‐6‐(1,1,7,7,‐tetramethyljulolidyl‐9‐enyl)‐4H‐pyran (DCJTB), one of the most efficient red‐emitting dopants, DCQTB exhibits red‐shifted fluorescence but blue‐shifted absorption. The unique characteristics of DCQTB with respect to DCJTB are utilized to achieve a red OLED with improved color purity and luminous efficiency. As a result, the device that uses DCQTB as dopant, with the configuration: indium tin oxide (ITO)/N,N′‐bis(1‐naphthyl)‐N,N′‐diphenyl‐1,1′‐biphenyl‐4,4′‐diamine (NPB; 60 nm)/tris(8‐quinolinolato) aluminum (Alq₃):dopant (2.3 wt %) (7 nm)/2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline (BCP; 12 nm)/Alq₃(45 nm)/LiF(0.3 nm):Al (300 nm), shows a larger maximum luminance (L_max = 6021 cd m^–2 at 17 V), higher maximum efficiency (η_max = 4.41 cd A^–1 at 11.5 V (235.5 cd m^–2)), and better chromaticity coordinates (Commission Internationale de l'Eclairage, CIE, (x,y) = (0.65,0.35)) than a DCJTB‐based device with the same structure (L_max = 3453 cd m^–2 at 15.5 V, η_max = 3.01 cd A^–1 at 10 V (17.69 cd m^–2), and CIE (x,y) = (0.62,0.38)). The possible reasons for the red‐shifted emission but blue‐shifted absorption of DCQTB relative to DCJTB are also discussed.     

White Electroluminescence from a Single‐Polymer System with Simultaneous Two‐Color Emission: Polyfluorene as the Blue Host and a 2,1,3‐Benzothiadiazole Derivative as the Orange Dopant

New single‐polymer electroluminescent systems containing two individual emission species—polyfluorenes as a blue host and 2,1,3‐benzothiadiazole derivative units as an orange dopant on the main chain—have been designed and synthesized. The resulting single polymers are found to have highly efficient white electroluminescence with simultaneous blue (λ_max = 421 nm/445 nm) and orange emission (λ_max = 564 nm) from the corresponding emitting species. The influence of the photoluminescence (PL) efficiencies of both the blue and orange species on the electroluminescence (EL) efficiencies of white polymer light‐emitting diodes (PLEDs) based on the single‐polymer systems has been investigated. The introduction of the highly efficient 4,7‐bis(4‐(N‐phenyl‐N‐(4‐methylphenyl)amino)phenyl)‐2,1,3‐benzothiadiazole unit to the main chain of polyfluorene provides significant improvement in EL efficiency. For a single‐layer device fabricated in air (indium tin oxide/poly(3,4‐ethylenedioxythiophene): poly(styrene sulfonic acid/polymer/Ca/Al), pure‐white electroluminescence with Commission Internationale de l'Eclairage (CIE) coordinates of (0.35,0.32), maximum brightness of 12 300 cd m^–2, luminance efficiency of 7.30 cd A^–1, and power efficiency of 3.34 lm W^–1 can be obtained. This device is approximately two times more efficient than that utilizing a single polyfluorene containing 1,8‐naphthalimide moieties, and shows remarkable improvement over the corresponding blend systems in terms of efficiency and color stability. Thermal treatment of the single‐layer device before cathode deposition leads to the further improvement of the device performance, with CIE coordinates of (0.35,0.34), turn‐on voltage of 3.5 V, luminance efficiency of 8.99 cd A^–1, power efficiency of 5.75 lm W^–1, external quantum efficiency of 3.8 %, and maximum brightness of 12 680 cd m^–2. This performance is roughly comparable to that of white organic light‐emitting diodes (WOLEDs) with multilayer device structures and complicated fabrication processes.     

Stable,Glassy, and Versatile Binaphthalene Derivatives Capable of Efficient Hole Transport,Hosting, and Deep‐Blue Light Emission

Organic light‐emitting diodes (OLEDs) have great potential applications in display and solid‐state lighting. Stability, cost, and blue emission are key issues governing the future of OLEDs. The synthesis and photoelectronics of a series of three kinds of binaphthyl (BN) derivatives are reported. BN_1–3 are “melting‐point‐less” and highly stable materials, forming very good, amorphous, glass‐like films. They decompose at temperatures as high as 485–545 °C. At a constant current density of 25 mA cm^?2, an ITO/BN₃/Al single‐layer device has a much‐longer lifetime (>80 h) than that of an ITO/NPB/Al single‐layer device (8 h). Also, the lifetime of a multilayer device based on BN₁ is longer than a similar device based on NPB. BNs are efficient and versatile OLED materials: they can be used as a hole‐transport layer (HTL), a host, and a deep‐blue‐light‐emitting material. This versatility may cut the cost of large‐scale material manufacture. More importantly, the deep‐blue electroluminescence (emission peak at 444 nm with CIE coordinates (0.16, 0.11), 3.23 cd A^?1 at 0.21 mA cm^?2, and 25200 cd m^?2 at 9 V) remains very stable at very high current densities up to 1000 mA cm^?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.     

Stable and Efficient White Electroluminescent Devices Based on a Single Emitting Layer of Polymer Blends

An efficient orange‐light‐emitting polymer (PFTO‐BSeD5) has been developed through the incorporation of low‐bandgap benzoselenadiazole (BSeD) moieties into the backbone of a blue‐light‐emitting polyfluorene copolymer (PFTO poly{[9,9‐bis(4‐(5‐(4‐tert‐butylphenyl)‐[1,3,4]‐oxadiazol‐2‐yl)phenyl)‐9′,9′‐di‐n‐octyl‐[2,2′]‐bifluoren‐7,7′‐diyl]‐stat‐[9,9‐bis(4‐(N,N‐di(4‐n‐butylphenyl)amino)phenyl)‐9′,9′‐di‐n‐octyl‐[2,2′]‐bifluoren‐7,7′‐diyl]}) that contains hole‐transporting triphenylamine and electron‐transporting oxadiazole pendent groups. A polymer light‐emitting device based on this copolymer exhibits a strong, bright‐orange emission with Commission Internationale de L'Eclairage (CIE) color coordinates (0.45,0.52). The maximum brightness is 13 716 cd m^–2 and the maximum luminance efficiency is 5.53 cd A^–1. The use of blends of PFTO‐BSeD5 in PFTO leads to efficient and stable white‐light‐emitting diodes—at a doping concentration of 9 wt %, the device reaches its maximum external quantum efficiency of 1.64 % (4.08 cd A^–1). The emission color remains almost unchanged under different bias conditions: the CIE coordinates are (0.32,0.33) at 11.0 V (2.54 mA cm^–2, 102 cd m^–2) and (0.31,0.33) at 21.0 V (281 mA cm^–2, 7328 cd m^–2). These values are very close to the ideal CIE chromaticity coordinates for a pure white color (0.33,0.33).     

Cover Picture: White Electroluminescence from a Single‐Polymer System with Simultaneous Two‐Color Emission: Polyfluorene as the Blue Host and a 2,1,3‐Benzothiadiazole Derivative as the Orange Dopant (Adv. Funct. Mater. 7/2006)

New single‐polymer electroluminescent systems containing two individual emission species—polyfluorenes as a blue host and 2,1,3‐benzothiadiazole derivative units as an orange dopant on the main chain—have been designed and synthesized by Wang and co‐workers on p. 957. The resulting single polymers are found to have highly efficient white electroluminescence with simultaneous blue and orange emission from the corresponding emitting species. A single‐layer device has been fabricated that has performance characteristics roughly comparable to those of organic white‐light‐emitting diodes with multilayer device structures. New single‐polymer electroluminescent systems containing two individual emission species—polyfluorenes as a blue host and 2,1,3‐benzothiadiazole derivative units as an orange dopant on the main chain—have been designed and synthesized. The resulting single polymers are found to have highly efficient white electroluminescence with simultaneous blue (λ_max = 421 nm/445 nm) and orange emission (λ_max = 564 nm) from the corresponding emitting species. The influence of the photoluminescence (PL) efficiencies of both the blue and orange species on the electroluminescence (EL) efficiencies of white polymer light‐emitting diodes (PLEDs) based on the single‐polymer systems has been investigated. The introduction of the highly efficient 4,7‐bis(4‐(N‐phenyl‐N‐(4‐methylphenyl)amino)phenyl)‐2,1,3‐benzothiadiazole unit to the main chain of polyfluorene provides significant improvement in EL efficiency. For a single‐layer device fabricated in air (indium tin oxide/poly(3,4‐ethylenedioxythiophene): poly(styrene sulfonic acid/polymer/Ca/Al), pure‐white electroluminescence with Commission Internationale de l'Eclairage (CIE) coordinates of (0.35,0.32), maximum brightness of 12 300 cd m^–2, luminance efficiency of 7.30 cd A^–1, and power efficiency of 3.34 lm W^–1 can be obtained. This device is approximately two times more efficient than that utilizing a single polyfluorene containing 1,8‐naphthalimide moieties, and shows remarkable improvement over the corresponding blend systems in terms of efficiency and color stability. Thermal treatment of the single‐layer device before cathode deposition leads to the further improvement of the device performance, with CIE coordinates of (0.35,0.34), turn‐on voltage of 3.5 V, luminance efficiency of 8.99 cd A^–1, power efficiency of 5.75 lm W^–1, external quantum efficiency of 3.8 %, and maximum brightness of 12 680 cd m^–2. This performance is roughly comparable to that of white organic light‐emitting diodes (WOLEDs) with multilayer device structures and complicated fabrication processes.     

Platinum Binuclear Complexes as Phosphorescent Dopants for Monochromatic and White Organic Light‐Emitting Diodes

Efficient blue‐, green‐, and red‐light‐emitting organic diodes are fabricated using binuclear platinum complexes as phosphorescent dopants. The series of complexes used here have pyrazolate bridging ligands and the general formula C^∧NPt(μ‐pz)₂PtC^∧N (where C^∧N = 2‐(4′,6′‐difluorophenyl)pyridinato‐N,C^2′, pz = pyrazole ( 1 ), 3‐methyl‐5‐tert‐butylpyrazole ( 2 ), and 3,5‐bis(tert‐butyl)pyrazole ( 3 )). The Pt–Pt distance in the complexes, which decreases in the order 1 > 2 > 3 , solely determines the electroluminescence color of the organic light‐emitting diodes (OLEDs). Blue OLEDs fabricated using 8 % 1 doped into a 3,5‐bis(N‐carbazolyl)benzene (mCP) host have a quantum efficiency of 4.3 % at 120 Cd m^–2, a brightness of 3900 Cd m^–2 at 12 V, and Commission Internationale de L'Eclairage (CIE) coordinates of (0.11, 0.24). Green and red OLEDs fabricated with 2 and 3 , respectively, also give high quantum efficiencies (～ 6.7 %), with CIE coordinates of (0.31, 0.63) and (0.59, 0.46), respectively. The current‐density–voltage characteristics of devices made using dopants 2 and 3 indicate that hole trapping is enhanced by short Pt–Pt distances (< 3.1 Å). Blue electrophosphorescence is achieved by taking advantage of the binuclear molecular geometry in order to suppress dopant intermolecular interactions. No evidence of low‐energy emission from aggregate states is observed in OLEDs made with 50 % 1 doped into mCP. OLEDs made using 100 % 1 as an emissive layer display red luminescence, which is believed to originate from distorted complexes with compressed Pt–Pt separations located in defect sites within the neat film. White OLEDs are fabricated using 1 and 3 in three different device architectures, either with one or two dopants in dual emissive layers or both dopants in a single emissive layer. All the white OLEDs have high quantum efficiency (～ 5 %) and brightness (～ 600 Cd m^–2 at 10 V).     

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.     

High‐Efficiency and Color Stable Blue‐Light‐Emitting Polymers and Devices

Novel fluorene‐based blue‐light‐emitting copolymers with an ultraviolet‐blue‐light (UV‐blue‐light) emitting host and a blue‐light emitting component, 4‐N,N‐diphenylaminostilbene (DPS) have been designed and synthesized by using the palladium‐ catalyzed Suzuki coupling reaction. It was found that both copolymers poly [2,7‐(9,9‐dioctylfluorene)‐alt‐1,3‐(5‐carbazolphenylene)] (PFCz) DPS1 and PFCz‐DPS1‐OXD show pure blue‐light emission even with only 1 % DPS units because of the efficient energy transfer from the UV‐blue‐light emitting PFCz segments to the blue‐light‐emitting DPS units. Moreover, because of the efficient energy transfer/charge trapping in these copolymers, PFCz‐DPS1 and PFCz‐DPS1‐OXD show excellent device performance with a very stable pure blue‐light emission. By using a neutral surfactant poly[9,9‐bis(6'‐(diethanolamino)hexyl)‐fluorene] (PFN‐OH) as the electron injection layer, the device based on PFCz‐DPS1‐OXD5 with the configuration of ITO/PEDOT:PSS/PVK/polymer/PFN‐OH/Al showed a maximum quantum efficiency of 2.83 % and a maximum luminous efficiency of 2.50 cd A^–1. Its CIE 1931 chromaticity coordinates of (0.156, 0.080) match very well with the NTSC standard blue pixel coordinates of (0.14, 0.08). These results indicate that this kind of dopant/host copolymer could be a promising candidate for blue‐light‐emitting polymers with high efficiency, good color purity, and excellent color stability.     

Efficient Bipolar Blue AIEgens for High‐Performance Nondoped Blue OLEDs and Hybrid White OLEDs

Blue organic luminescent materials play a crucial role in full‐color display and white lighting but efficient ones meeting commercial demands are very rare. Herein, the design and synthesis of tailor‐made bipolar blue luminogens with an anthracene core and various functional groups are reported. The thermal stabilities, photophysical properties, electronic structures, electrochemical behaviors, carrier transport abilities, and electroluminescence performances are systematically investigated. The luminogen TPE‐TAPBI containing a tetraphenylethene moiety shows aggregation‐induced emission, while another luminogen TriPE‐TAPBI bearing a triphenylethene unit exhibits light aggregation‐caused quenching. In comparison with TriPE‐TAPBI, TPE‐TAPBI has stronger blue emission in neat film and functions more efficiently in nondoped organic light‐emitting diodes (OLEDs). High maxima current, power, and external quantum efficiencies of 7.21 cd A^?1, 6.78 lm W^?1, and 5.73%, respectively, are attained by the nondoped blue OLED of TPE‐TAPBI (CIE_x,y = 0.15, 0.16). Moreover, efficient two‐color hybrid warm white OLEDs (CIE_x,y = 0.457, 0.470) are achieved using TPE‐TAPBI neat film as the blue‐emitting component, which provide total current, power, external quantum efficiencies of up to 70.5 lm W^?1, 76.0 cd A^?1, and 28% at 1000 cd m^?2, respectively. These blue and white OLEDs are among the most efficient devices with similar colors in the literature.     

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.     

Origin of the Exclusive Ternary Electroluminescent Behavior of BN‐Doped Nanographenes in Efficient Single‐Component White Light‐Emitting Electrochemical Cells

White‐light‐emitting electrochemical cells (WLECs) still represent a significant milestone, since only a few examples with moderate performances have been reported. Particularly, multiemissive white emitters are highly desired, as a paradigm to circumvent phase separation and voltage‐dependent emission color issues that are encountered following host:guest and multilayered approaches. Herein, the origin of the exclusive white ternary electroluminescent behavior of BN‐doped nanographenes with a B₃N₃ doping pattern (hexa‐perihexabenzoborazinocoronene) is rationalized, leading to one of the most efficient (≈3 cd A^?1) and stable‐over‐days single‐component and single‐layered WLECs. To date, BN‐doped nanographenes have featured blue thermally activated delayed fluorescence (TADF). This doping pattern provides, however, white electroluminescence spanning the whole visible range (x/y CIE coordinates of 0.29–31/0.31–38 and average color rendering index (CRI) of 87) through a ternary emission involving fluorescence and thermally activated dual phosphorescence. This temperature‐dependent multiemissive mechanism is operative for both photo‐ and electroluminescence processes and holds over the device lifespan, regardless of the device architecture, active layer composition, and operating conditions. As such, this work represents a new stepping‐stone toward designing a new family of multiemissive white emitters based on BN‐doped nanographenes that realizes one of the best‐performing single‐component white‐emitting devices compared to the prior‐art.