Deep-blue OLEDs Research Articles

The application of halogenated 3,3′-dimethyl-9,9′-bianthracene derived materials in deep-blue OLEDs

3,3′-Dimethyl-9,9′-bianthracene (MBAn) is a non-donor-acceptor type bipolar deep blue fluorophore with a twisted conformation that can effectively prevent π-π stacking quenching, thereby enhancing the luminescence efficiency. And the introduction of halogen elements can increase the electron affinity of the material, thus effectively improving the electron mobility of the material, which contributes to the better optoelectronic performance of organic light-emitting diodes (OLEDs). Five MBAn derivatives were synthesized by altering the positions and numbers of halogen substituents on the two phenyl rings attached to the MBAn core at positions 9 and 9'. The photophysical, electrochemical, thermal stability and theoretical studies of these five derivatives were carried out. The OLED using 10,10′-bis(4-chlorophenyl)-3,3′-dimethyl-9,9′-bianthracene (MBAn-4-Cl) as the emitter shows a comparable electroluminescence spectrum peaked at 440 nm (FWHM = 52 nm) and a maximum external quantum efficiency (EQEmax) of 5.25% at Commission Internationale de l’Éclairage (CIE) coordinates of (0.143, 0.067), which matches the National Television Standards Committee (NTSC) standard (0.14, 0.08) very well.

Synthesis and luminescent properties of spiroacridine-imidazole derivatives

Two spiroacridine-imidazole derivatives (SAF-BI and SAF-PI) were prepared and their potential for application in deep-blue OLEDs was explored.

4.2: A 9‐(4‐diphenylphosphinylphenyl)anthracene derivative as a blue emitter host and a hole‐blocking layer in Deep Blue OLEDs

We investigated 10‐(4‐phenylphenyl)‐9‐(3‐diphenylphosphinyl‐phenyl)anthracene as a host material in the emitting layer and a hole‐blocking layer in deep blue OLEDs, respectively. By contrast, introducing a thin layer of this triphenylphosphine oxide moiety‐modified anthracene derivative as the hole blocker exhibits a maximum external quantum efficiency of 5.49% with CIE (0.126, 0.118) and in particular, high device stability with lifetime LT95 of ca. 540 h @ 1000 cd m–2.

TADF emitters based on a tri-spiral acridine donor and a spiro-B-heterotriangulene acceptor with high horizontal dipole orientation ratios and high efficiencies in deep-blue OLEDs

Linearly expanded rigid TADF emitters, composed of a tri-spiral acridine donor and a spiro-fluorenyl-B-heterotriangulene acceptor, exhibit very high horizontal dipole orientation ratios, thereby achieving high efficiencies in deep-blue OLEDs.

Deep Blue Phosphorescence from Platinum Complexes Featuring Cyclometalated N-Pyridyl Carbazole Ligands with Monocarborane Clusters (CB11H12-).

The utilization of deep blue phosphorescent materials in high-performance displays and solid-state lighting requires high quantum efficiencies and color purities. Here, we describe the preparation and luminescent properties of novel platinum triplet emitters featuring cyclometalated N-pyridyl-carbazole ligands functionalized with closo-monocarborane clusters [CB11H12]-. All reported complexes were fully characterized by using standard small molecule techniques (UV-vis, cyclic voltammetry, nuclear magnetic resonance (NMR), high-resolution mass spectrometry (HRMS)), and their solid-state structures were elucidated by X-ray diffraction. These platinum phosphors emit in the blue region of the visible wavelength spectrum in both the solid and solution states. Complex 4a exhibits the highest luminous efficiency at λem = 439 nm with a photoluminescent quantum yield (PLQY) of 60% by dispersing in a PMMA matrix. Electrochemical and computational studies of complexes 4a and 4b revealed that the blue phosphorescence originates mainly from intraligand 3π → π* (3ILCT) transitions with relatively small 3MLCT mixing. A deep-blue OLED containing 4a as the light-emitting dopant was successfully fabricated using a solution-processed method, and the device exhibited blue photoluminescence with CIE coordinates of (0.17, 0.15) and a maximum external quantum efficiency (EQEmax) value of 6.2%. This article represents the pioneering study of a deep blue PhOLED using a Pt complex bearing a closo-monocarborane anion substituent, providing a new avenue into the preparation of novel triplet emitters based on boron-rich cluster anions.

Dual role of novel hole-transporting and deep-blue emitting materials based on twisted binaphthyl

Three novel deep blue-emitting materials from binaphthyl derivatives, namely BFS, BNS and BNF, were designed and synthesized. Due to their rigid structure, all the materials exhibit high thermal stability with Td exceed 440 °C and Tg as high as 153 °C, 149 °C and 140 °C, respectively. They also show appropriate HOMO and LUMO energy level, excellent amorphous stability and outstanding solubility in common organic solvents. These novel materials are highly emissive in both solution and solid states, with deep blue emissions peaked at ∼450 nm. Deep-blue OLEDs using the novel materials as emitter resulted in efficient CE, EQE and luminance. The BFS, BNS and BNF based devices show good EL performances with the Lmax of 857 cd/m2 (CEmax of 0.3 cd/A), Lmax of 1038 cd/m2 (CEmax of 0.5 cd/A), and Lmax of 3717 cd/m2 (CEmax of 0.5 cd/A), respectively. They should be promising hole-transport and deep blue-emitting materials for OLED devices.

N–C chelated tetraaryl-pyrazole based organoboranes: A new class of aggregation induced enhanced emission materials

Luminescent materials, especially aggregation induced emissive materials attract considerable attention owing to their potential applications in optoelectronic devices, cell imaging, fluorescent sensors and so on. Hence, new aggregation induced emissive materials are in high demand. Here, we report, a series of N,C-chelated B–N coordinated tetraaryl pyrazoles (TAP-B1 to TAP-B4). The cumulative effect of the rigid organization of the phenyl groups imparts aggregation induced emissive behaviour and the extended conjugation imposed by the B–N coordination makes them as attractive new aggregation induced molecules. Deep blue OLED with CIE of (0.15, 0.15) is fabricated using TAP-B4 exhibits reduced efficiency roll off and outstanding luminance of up to 8024 cd/m2 and remarkable maximum EL efficiencies of 4.5 lm/W and 6.1 cd/A with the maximum external quantum efficiency of 4.8%.

Molecular Engineering for the Development of a Discotic Nematic Mesophase and Solid-State Emitter in Deep-Blue OLEDs.

A unique strategy for the attainment of a discotic nematic (ND) mesophase is reported consisting of a central benzene core to which are attached two 4-alkylphenyl and two 4-pentylbiphenyl moieties diagonally via alkynyl linkers. The rotational nature and incompatibility of unequal phenylethynyl units led to the disruption of π-π interactions within cores that aids to the realization of ND phase and favors high solid-state emission. When used in OLEDs, compounds act as an efficient solid-state pure deep-blue emitter with Commission Internationale de L'Eclairage (CIEx,y) coordinates of (0.16, 0.07).

Rational molecular design of bipolar phenanthroimidazole derivatives to realize highly efficient non-doped deep blue electroluminescence with CIEy ˂ 0.06 and EQE approaching 6%

We report a series of novel phenanthroimidazole (PI) based bipolar deep blue-emitting compounds. The structure-property relationship is systematically studied. A star-shape steric group tetraphenylbenzene (TPB) is substituted to the C2 position of PI, which contributes to high-efficiency deep blue photoluminescence (PL) in solid state; while electron-withdrawing or donating groups are attached to the N1 position to realized tunable charge transfer character for high exciton utilization. Among all the emitters, the non-doped electroluminescent devices based on TPBPPI-PY and TPBPPI-PBI display superior EQE of 5.70% and 5.94% with color coordinates of (0.16, 0.049) and (0.16, 0.059), respectively. These performances are among the best deep blue OLEDs with CIEy < 0.06.

Tailored deep blue OLEDs characteristics with doping engineering in fluorescent dyes based on DMPPP: towards manufacturable solid-state lighting building blocks

We report on a deep blue OLED paradigm where the typical electrical and optical characteristics can be tailored with doping engineering. The devices are fabricated with a representative structure of ITO/m-MTDATA (20 nm) NPB (10 nm)/DMPPP:BCzVBi (d nm, x wt%)/Bphen (30 nm)/Cs2CO3:Ag2O (20 wt%, 1 nm)/Al (100 nm). Complementary studies are performed on the properties of deep blue OLEDs with specific doping concentrations (x = 2, 5, 8 and 10) and various doping layer thicknesses (d = 3, 5, 15 and 20). High luminance and efficiency deep blue OLEDs are obtained with tailored energy transfer between the host and the guest in the emissive layer when the x and d was 8 and 15, respectively. The developed device demonstrate a maximum current efficiency of 3.53 cd/A with a maximum luminance of 16,570 cd/m2. The CIE coordinates of the device are well within the deep blue region when the voltage is changed from 6 to 11 V. The CIEx,y is (0.155, 0.128) at the maximum luminance. Our systematic studies and complementary engineering investigations upon highly efficient deep blue OLEDs open new opportunities towards innovative applications in an industrial level available with optimized device integration among performance, dimension and cost in a variety of fields, e.g., flat panel display, smart wearable devices and human–machine interfaces lighting.

Deep-Blue High-Efficiency TTA OLED Using Para- and Meta-Conjugated Cyanotriphenylbenzene and Carbazole Derivatives as Emitter and Host.

Elaboration of the appropriate host materials proved to be not less important for the fabrication of a highly efficient OLED than the design of emitters. In the present work, we show how by simple variation of molecular structure both blue emitters exhibiting delayed fluorescence and ambipolar high triplet energy hosts can be obtained. The compounds with a para-junction revealed higher thermal stability (TID up to 480 °C), lower ionization potentials (5.51-5.60 eV), exclusively hole transport, and higher photoluminescence quantum efficiencies (0.90-0.97). Meta-linkage leads to ambipolar charge transport and higher triplet energies (2.82 eV). Introduction of the accepting nitrile groups in the para-position induces intensive delayed fluorescence via a triplet-triplet annihilation up-conversion mechanism. By utilization of the para-substituted derivative as an emitter and the meta-substituted isomer as the host, a deep-blue OLED with the external quantum efficiency of 14.1% was fabricated.

Arylfluorenyl-substituted metoxytriphenylamines as deep blue exciplex forming bipolar semiconductors for white and blue organic light emitting diodes

Arylfluorenyl-substituted triphenylamines were prepared by acid promoted Friedel-Crafts-type substitution reaction. The synthesized compounds were found to be capable of glass formation with glass transition temperatures above 152 °C. The ionization potentials of the layers of the derivatives were found to be in the range of 5.25–5.41 eV. Time-of-flight hole and electron drift mobility values of the layer of tris[3-methoxy-4-(9-phenyl-9-fluorenyl)phenyl]amine well exceeded 10−3 cm2/V at high electric fields at room temperature. The results obtained by means of density functional theory calculations were used to discuss on the charge-transporting and optical properties of the compounds. Deep blue exciplexes formed by the newly synthesized arylfluorenyl-substituted triphenylamines and the known electron-transporting materials 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) or 4,7-diphenyl-1,10-phenanthroline (Bphen) were discovered and studied. Based on these exciplexes, we propose an original structure of cold white OLED with CIE chromaticity coordinates ranging from (0.286, 0.378) to (0.24, 0.29) depending on applied voltages. Electroluminescence spectra of cold white OLED consist of deep blue and green emissions which originate from bulk and interface. The origin of green emission is thermally activated delayed fluorescence (TADF) from exciplex formed between 4,4′,4″-tris[3-methylphenyl(phenyl)amino]triphenylamine (m-MTDATA) and Bphen. Based on the newly discovered exciplex emitters, deep blue OLED with the electroluminescence maximum at 428 nm and with CIE chromaticity coordinates of (0.179; 0.104) was fabricated. The cold white and deep blue devices showed external quantum efficiencies of 2.55% and 1.2%, respectively.

Blue Emitting Materials Based on Naphthylanthracene Derivatives Containing Electron-Withdrawing Fluorobenzenes.

We have designed and synthesized three blue emitters based on 9-naphthylanthracene derivatives connected with various electron-withdrawing group such as 4-fluorobenzene, 2,4-difluorobenzene and 2,3,4,5,6-pentafluorobenzene (1-3). Multilayered OLEDs with the structure of ITO (180 nm)/NPB (50 nm)/Blue materials 1-3 (30 nm)/TPBi (15 nm)/Liq (2 nm)/AI (100 nm) have been fabricated to investigate their electroluminescent properties. In particular, the device using 3 showed efficient blue electroluminescent properties with a luminous, power, external quantum efficiency and CIE coordinates of 0.71 cd/A, 1.98 Im/W, 1.34% at 20 mA/cm2 and (x = 0.16, y = 0.20) at 10.0 V, respectively. In addition, a deep blue OLED using 1 with CIE coordinates (x = 0.15, y = 0.11) at 10.0 V exhibited a luminous, power, external quantum efficiency of 2.12 cd/A, 3.04 Im/W and 1.17% at 20 mA/cm2, respectively.

Pyrene based materials for exceptionally deep blue OLEDs

A 2,7-functionalized pyrene-based emitter for highly efficient OLEDs has been developed. It offers an exceptional deep blue photoluminescence (CIE: x = 0.16, y = 0.024) and good external quantum efficiency (EQE) of 3.1% when employed in a guest–host system OLED.

Preparation and Characterization of Novel Polyfluorenes Derivatives Containing Phenanthro[9,10-d]imidazole Group for Deep Blue-Light-Emitting Polymers

A series of novel polyfluorenes derivatives containing different ratio of phenanthro -[9,10-imidazole (PI) group on backbone are designed, synthesized and well characterized. Comparing with the class blue polymer PF, they all exhibit deep blue emission in solution and film with high PL efficiency, and show better film forming ability because of the insert of bulky substituent on PI unit by the AFM measurement. The CV results of all compounds deliver balanced carriers injection ability, and the decreased LUMO levels and improved HOMO levels are observed, which is befit of the preparation of high performance deep blue OLED.

21.1: Electron‐Transport Layers with Air‐Stable Dopants for Display Applications

AbstractWe report on a new class of doped electron transport layers for display applications. New air‐stable dopant materials are presented together with matching host material. This new ETL concept allows for optimum balance of long lifetime and high efficiency. Device data for top‐emission deep blue OLEDs are shown and options for optimization of OLEDs according to specific application requirements are discussed.

Phthalonitrile based fluorophores as fluorescent dopant emitters in deep-blue OLEDs: Approaching the NTSC standard for blue

Unprecedented phthalonitrile based fluorophores are reported and studied for incorporation into organic light emitting diodes. The phthalonitriles were obtained using a very simple synthetic procedure and were found to be highly fluorescent with quantum yields approaching unity; they are also thermally stable and electrochemically active. When incorporated into OLEDs as fluorescent dopants, the resulting devices have good device efficiencies and emit in the deep-blue area of the spectrum with CIE coordinates that are close to the NTSC standard for blue.

New Deep Blue Emitting Materials Based on Indenopyrazine Core with High Thermal Stability

New deep blue emitting materials 2,8-bis(3,5-diphenylphenyl)-6,6,12,12-tetraethyl-6,12-dihydrodiindeno[1,2-b:1',2'-e]pyrazine (DPP-EPY) and 2,8-bis(3',5'-diphenylbiphenyl-4-yl)-6,6,12,12-tetraethyl-6,12-dihydrodiindeno[1,2-b:1',2'-e]pyrazine (DPBP-EPY) were synthesized through introduction of m-terphenyl or triphenylbenzene bulky side groups in a new indenopyrazine core. These materials all showed high thermal stability and highly reduced intermolecular interaction. DPP-EPY and DPBP-EPY showed PL maxima of 456 nm and 460 nm in deep blue region and narrow PL spectra with full-width at half-maximum (FWHM) of 46 nm and 52 nm, respectively. As a result of making non-doped OLED devices using these synthesized materials as emitting layers, DPP-EPY showed EL spectrum of 452 nm, very narrow FWHM of 46 nm, luminance efficiency of 1.04 cd/A with current density of 10 mA/cm2 and CIE coordinate of (0.161, 0.104), creating a deep blue OLED close to the National Television System Committee (NTSC) blue standard.

Deep-blue OLEDs using novel efficient spiro-type dopant materials

The deep blue fluorescent spiro-type dopant materials N,N,N′ ,N′-tetraphenylspiro[fluorene-7,9′-benzofluorene] ( SFBF)-5,9-diamine (BD-6DPA), N,N′-di-(2-naphthyl)- N,N′-diphenyl- SFBF-5,9-diamine (BD-6NPA), N,N′-diphenyl- N,N′-di- m-tolyl- SFBF-5,9-diamine (BD-6MDPA) and N,N′-diphenyl- N,N′-bis(4-(trimethylsilyl)phenyl)- SFBF-5,9-diamine (BD-6TMSA) were designed and successfully prepared by amination reactions. The EL characteristics of MADN as the blue host material doped with the above blue dopant materials were evaluated. The electroluminescence spectra of ITO/ N,N′-diphenyl- N,N′-bis-[4-(phenyl- m-tolyl-amino)-phenyl]-biphenyl-4,4′-diamine (DNTPD/ N,N′-di(1-naphthyl)- N,N′-diphenylbenzidine (NPB)/2-methyl-9,10-di(2-naphthyl)anthracene (MADN):BD-6MDPA/tris(8-hydroxyquinoline)aluminum (Alq 3)/LiF/Al devices show a narrow emission band with a full width at half maximum of 48 nm and a λ max( ε) = 463 nm. The device obtained from MADN doped with BD-6MDPA showed a good color purity (0.135, 0.156), high luminance efficiency (9.11 cd/A at 6.5 V) and high external quantum efficiency (8.16%).

A highly efficient deep blue fluorescent OLED based on diphenylaminofluorenylstyrene-containing emitting materials

We have designed and synthesized five blue emitters based on diphenylaminofluorenylstyrene emitting core groups. Multilayered OLEDs were fabricated using these materials as dopants in a 2-methyl-9,10-di(naphthen-2-yl)anthracene (MADN) host. One of them in particular a deep blue OLED using dopant 9-[4-(2-diphenylamino-9,9-diethylfluoren-7-yl)phenyl]-9-phenylfluorene ( 3) at 15% doping concentration exhibited a maximum luminance of 4720 cd m −2 at 9.0 V, a luminous efficiency of 5.3 cd A −1 at 20 mA cm −2, a power efficiency of 2.9 lm W −1 at 20 mA cm −2, an external quantum efficiency of 4.8% at 20 mA cm −2, and CIE coordinates ( x = 0.15, y = 0.13) at 8.0 V. Furthermore, this deep blue device had very stable CIE coordinates of ( x = 0.15, y = 0.13) that did not vary with doping concentration from 5% to 15%.