Blue Phosphorescent Organic Light-emitting Diodes Research Articles

Tuning the Photophysical Properties of Homoleptic Tris-Cyclometalated Ir(III) Complexes by Facile Modification of the Imidazo-Phenanthridine and Their Application to Phosphorescent Organic Light-Emitting Diodes.

To explore the excited-state electronic structure of the blue-emitting Ir(dmp)3 dopant material (dmp = 3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridine), which is notable for durable blue phosphorescent organic light-emitting diode (PhOLED), a series of homoleptic dmp-based Ir(III) complexes (DMP–R, tris[3-(2,6-dimethylphenyl)-7-R-imidazo[1,2-f]phenanthridin-12-yl-κC12,κN1]iridium, R = H, CH3, F, and CF3) were prepared by introducing an electron-donating group (EDG; −CH3) or an electron-withdrawing group (EWG; −F and −CF3) at the 7-position of the imidazo-phenanthridine ligand. The photophysical analysis demonstrated that the alteration from EDG to EWGs led to redshifted structureless emission profiles, which were correlated with variations in the 3MLCT/3ILCT ratio in the T1 excited state. From electrochemical studies and density functional theory calculations, it turned out that the excited-state nature of the dmp-based Ir(III) complexes was significantly affected by the inductive effect of the 7-substituent of the cyclometalating dmp ligand. As a result of the lowest unoccupied molecular orbital energy stabilization by the EWGs that suppressed the non-radiative pathway from the emissive triplet excited state to the 3d–d state, the F- and CF3-modified Ir(dmp)3 complexes (DMP–F and DMP–CF3) showed quantum yields of 27–30% in the solution state, which were at least 4- or 5-fold higher than those shown by DMP–H and DMP–CH3. A PhOLED device based on DMP–CF3 [CIE chromaticity (0.17, 0.39)], which demonstrated a distinct 3MLCT characteristic, exhibited better electroluminescent efficiencies with an external quantum efficiency of 13.5% than that based on DMP–CH3.

Low Efficiency Roll‐Off Blue Phosphorescent OLEDs at High Brightness Based on [3+2+1] Coordinated Iridium (III) Complexes

AbstractA new series of blue phosphorescent cyclometalated [3+2+1] coordinated iridium (III) complexes containing 2‐(2′,4′‐difluoropyridyl) pyridine derivatives have been designed and synthesized to investigate their structure–property relationship on the nature of excited states and tune their emission wavelengths from saturated‐blue to sky‐blue region at 437−489 nm. These complexes exhibit high photoluminescent quantum yields (PLQYs) of up to 90% and short excited state lifetime in the range of 2−5 µs in polymethylmethacrylate (PMMA) thin films. Sky‐blue organic light‐emitting diodes (OLEDs) based on such pyridine‐containing [3+2+1] iridium (III) dopants have exhibited maximum external quantum efficiencies (EQEmax) and current efficiency (CE) of 17.3% and 42.3 cd A–1, respectively. To note, very small efficiency roll‐off value from 4.3% to 19.7% is achieved at the luminance level of 1000 cd m–2. The well‐balanced electron and hole injection currents, the short lifetime of excited excitons, and wide recombination zone by leveraging the obtained iridium (III) dopants and exciplex co‐host have greatly decreased the accumulation of triplet excitons at the high luminescence level, leading to dramatically reduced efficiency roll‐off. It is anticipated that this work provides new insights into the design of saturated‐blue‐emitting iridium (III) complexes with reduced efficiency roll‐off in their fabricated OLEDs.

Exceptionally stable blue phosphorescent organic light-emitting diodes

Exceptionally stable blue phosphorescent organic light-emitting diodes

Are pure hydrocarbons the future of host materials for blue phosphorescent organic light-emitting diodes?

This Chemistry Frontiers deals with a new generation of host materials for phosphorescent OLEDs only constituted with carbon and hydrogen atoms, which can be beneficial for the future development of the OLED industry.

Unprecedentedly Long Lifetime Over 13,000 H for Multiple Energy Transfer Channels in Deep Blue Phosphorescence Organic Light-Emitting Diodes with IR Complex Under Ciey of 0.17

Unprecedentedly Long Lifetime Over 13,000 H for Multiple Energy Transfer Channels in Deep Blue Phosphorescence Organic Light-Emitting Diodes with IR Complex Under Ciey of 0.17

Rational design of blocking groups for high triplet energy n-type host materials

The effect of blocking groups on the device lifetime and efficiency of blue phosphorescent organic light-emitting diodes (PhOLEDs) was investigated by synthesizing electron transport-type hosts with different blocking groups.

Effect of PEDOT:PSS on the performance of solution-processed blue phosphorescent organic light-emitting diodes with an exciplex host

The acidity of the PEDOT:PSS hole injection layer was found to effect the performance of efficient solution-processed organic light-emitting diodes incorporating a light-emitting layer composed of a blue phosphorescent dendrimer:exciplex host blend.

Blue heteroleptic iridium(iii) complexes for OLEDs: simultaneous optimization of color purity and efficiency

The synergistic regulation of cyclometalating ligands and ancillary ligand optimized both the blue color purity and high efficiencies of iridium complexes. A high EQE of 28.0% with CIE (0.16, 0.21) was achieved in a blue phosphorescent OLED.

Bicarbazole-cyanopyridine based bipolar host materials for green and blue phosphorescent OLEDs: influence of the linking style between P- and N-type units

Bicarbazole and cyanopyridine were used to construct bipolar host materials. Ortho-linkage generated more balanced charge transportations and sufficiently high triplet energy (3.05 eV), and finally led to high EQEs of 15.9% and 22.6% in sky-blue and green phosphorescent OLEDs.

Highly efficient blue and white phosphorescent organic light-emitting diodes with low-efficiency roll-off utilizing thermally activated delayed fluorescent-based co-host architecture

Highly efficient blue phosphorescent organic light-emitting diodes (PhOLEDs) with reduced efficiency roll-off are still challenging. A blue phosphor of (cyanato-κO)[3,5-difluoro-2-(2-pyridinyl-κN)phenyl-κC][[1,1'-(1,3-phenylene-κC2)bis[3-butyl-2,3-dihydro-1H-imidazolato-κC2]](5-)]-iridium complex is utilized as the blue emitter to fabricate highly efficient blue PhOLEDs. Especially, it is first utilized for white PhOLEDs with superior device performance. The realized blue PhOLED employing a novel TADF co-host system achieves maximum power efficiency (PE) of 43.3 lm/W and the PE still remains 26.3 lm/W at 1000 cd/m2, which are 1.9 and 2.5 times higher than that of blue PhOLED using conventional phosphor single-host structure. Furthermore, the current efficiency (CE) roll-off of the blue PhOLED with TADF co-host architecture is only 2.2% at 1000 cd/m2, which can be assigned to the balanced charge carriers injection and transport. The final white device obtained the maximum CE of 46.1 cd/A, PE of 48.1 lm/W, and a low roll-off of 1.9% at 1000 cd/m2. We also systemically investigate the energy transfer mechanism and exciton distribution of the devices. It was found that our proposed device structure could effectively promote the Förster energy transfer mechanism and the even distribution of excitons. We firmly believe that our work may bring light to the future development of highly efficient PhOLEDs with simultaneous low roll-off.

Quantitative Correlation of Triplet Exciton Management in Host with the Device Lifetime of Blue Phosphorescent Organic Light‐Emitting Diodes

AbstractThe improvement of the device stability of blue phosphorescent organic light‐emitting diodes (PhOLEDs) has proven to be a challenging issue in terms of enhancing the efficiency of blue organic light‐emitting diodes in practical applications. This work comprehensively investigates the exciton dynamics of electroplex hosts and quantitatively correlates the steady‐state triplet excitons in the host with the device lifetime of state‐of‐the‐art blue PhOLEDs. The kinetic processes of electrically generated singlet excitons, triplet excitons, and polarons explored via transient electroluminescence and numerical modeling reveal that the triplet exciton density in the host is governed by reverse intersystem crossing and the triplet–triplet annihilation rates. A degradation modeling that takes into account the simultaneous material degradation due to the triplet excitons in the host and the dopant is newly established. The results indicate that the suppressed host degradation due to the reduction (1.5×) in host triplet excitons leads to enhanced operational stability. The characterization method and the numerical modeling in this work facilitate the determination of the exciton and polaron behavior of the host and allow for predicting the host‐dependent device lifetime of PhOLEDs for specific host materials.

A novel benzo[4,5]furo[3,2-d]pyrimidine-based host as a n-type host for blue phosphorescent organic light-emitting diodes

An electron-transport-type host was synthesized using a benzo[4,5]furo[3,2-d]pyrimidine (BFP) core to develop a high triplet energy host. The host was designed to have both the tetraphenylsilyl blocking group and the hole-transport-type carbazole group. In the device application, the host was used as an electron-transport-type host mixed with a hole-transport-type 3,3†-di(9H-carbazol-9-yl)-1,1†-biphenyl (mCBP) host in the blue phosphorescent organic light-emitting diodes (PhO-LEDs) doped with a [[5-(1,1-dimethylethyl)-3-phenyl-1H-imidazo[4,5-b]pyrazin-1-yl-2(3H)-ylidene]-1,2-phenylene]bis-[[6-(1,1-dimethylethyl)-3-phenyl-1H-imidazo[4,5-b]pyrazin-1-yl-2(3H)-ylidene]-1,2-phenylene]iridium (Ir(cb)3) blue phosphor. As a result, the mCBP:CzBFPmSi mixed host showed high external quantum efficiency over 20% at 1000 cd m−2 and low efficiency roll-off in the blue PhOLEDs.

Benzonitirile modified N type host for exciplex host to enhance efficiency and lifetime in blue phosphorescent organic light-emitting diodes

Benzonitirile modified host materials, 3-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-(triphenylsilyl)benzonitrile (CNmSi-Trz), 3-(4-(dibenzo[b,d]furan-2-yl)-6-phenyl-1,3,5-triazin-2-yl)-5-(triphenylsilyl)benzonitrile (CNmSi-2DBF-Trz) and 3-(4-(dibenzo[b,d]furan-4-yl)-6-phenyl-1,3,5-triazin-2-yl)-5-(triphenylsilyl)benzonitrile (CNmSi-4DBF-Trz), were synthesized for improved efficiency and lifetime in blue phosphorescent organic light-emitting diodes (PhOLEDs). Triazine and benzonitrile units were introduced commonly to the three host materials for electron transporting properties. The three hosts were applied to mixed host as electron transport type hosts with a hole transport type 3,3-di(9H-carbazol-9-yl)biphenyl (mCBP) for blue PhOLEDs. They formed exciplex with mCBP, and the exciplex of CNmSi-2DBF-Trz with mCBP showed high triplet energy above 2.9 eV. As a result, the blue PhOLEDs fabricated with the CNmSi-2DBF-Trz host achieved high EQE over 23% and 650 h lifetime up to 70% of initial luminance at 200 cd/m2 using the exciplex host system with mCBP.

Universally applicable small-molecule co-host ink formulation for inkjet printing red, green, and blue phosphorescent organic light-emitting diodes

For organic light-emitting diodes (OLEDs), inkjet printing technology is being developed as an alternative to the traditional vacuum evaporation, because of its precise patterning, high-efficient material utilization, large-area compatibility and low-cost. In this work, we report a universal ink formulation of small-molecule co-host and binary solvents for red, green and blue phosphorescent OLEDs. Moreover, the effect of hole-transporting layers on the ink spreading, film uniformity and exciton confinement ability is investigated. Furthermore, a large-area (170 mm × 170 mm) and homogeneous light-emitting film is inkjet-printed. Finally, red, green and blue OLEDs are successfully constructed using these optimized ink formulations on the solvent resistance hole-transporting layer. This work can reduce the complexity to adjust the host materials and solvents for different color inks, and could be applied in large-area and low-cost OLED displays with high resolution. ● A small-molecule co-host system of TCTA and 26DCzPPy is proposed for red, green and blue phosphorescent dopants. ● The binary solvents of o -dichlorobenzene and 1-chloronaphthalene are formulated to optimize the ink properties. ● The large-area light-emitting film was inkjet-printed, and OLEDs were constructed using these red, green and blue inks.

Room-temperature corrugated indium zinc oxide anode to achieve high-efficiency blue phosphorescent organic light-emitting diodes

A corrugated indium zinc oxide thin film was fabricated on a glass substrate at room temperature for use in a blue phosphorescent organic light-emitting device (OLED) to facilitate device efficiency in term of the external quantum efficiency (EQE) of the device, which increased from 28.77% to 34.33% after the fabrication of the aforementioned layer. Furthermore, a remarkably high EQE of 52.51% was achieved through external light extraction by attaching a hemispheric macrolens on the substrate of the device. Consequently, the efficiency of the developed blue phosphorescent OLED became 1.83 times higher than that of a planar counterpart. Moreover, this finding was verified through theoretical analyses, that indicated the underlying light extraction physics was attributed to the efficient extraction of trapped light from the surface plasmon polariton, waveguide, and substrate modes. (submitted to Organic Electronics).

Triplet Exciton Upconverting Blue Exciplex Host for Deep Blue Phosphors.

A thermally activated delayed fluorescence (TADF)-type exciplex host employing a novel electron-transport type (n-type) type host managing positive polarons and stabilizing excitons was developed to elongate the device lifetime of deep blue phosphorescent organic light-emitting diodes (PhOLEDs). The bipolar n-type host was designed to prevent hole leakage and secure hole stability while being stabilized under excitons by introducing a CN-modified carbazole moiety as a weak donor. The TADF-type exciplex host-based blue PhOLEDs showed high (above 20 %) quantum efficiency with a deep blue color coordinate of (0.14, 0.16) and elongated device lifetime. The device operational lifetime of the blue PhOLEDs bearing the TADF-type exciplex host was extended by more than twice compared to that of the exciplex-free unipolar host. This work suggested a design concept of the n-type host to develop the TADF-type exciplex host for deep blue phosphors to reach a long lifespan in the deep blue PhOLEDs.

Iridium(III)-Catalyzed Diarylation/Annulation of Benzoic Acids: Facile Access to Multi-Aryl Spirobifluorenes as Pure Hydrocarbon Hosts for High-Performance OLEDs.

Herein disclosed is the first example of diarylation/annulation of benzoic acids via an iridium catalyst system. This protocol provides a step-economic and highly efficient pathway to 1-aryl, 1,3-diaryl, 1,7-diaryl and 1,3,7-triaryl spirobifluorenes from readily available starting materials. The applications of multi-aryl spirobifluorenes as pure hydrocarbon (PHC) hosts for red, green, and blue (RGB) phosphorescent organic light-emitting diodes (PhOLEDs) were explored. Due to high triplet energies, 1,3-diaryl spirobifluorenes exhibit the potential as the host material of blue PhOLEDs. 1,7-Diaryl spirobifluorene can serve as the host of green PhOLEDs. 1,3,7-Triaryl spirobifluorene is a high-performance host for red PhOLEDs, which exhibits a high external quantum efficiency (EQE) up to 27.3 %. This work not only exemplifies the great potential of multi-aryl spirobifluorenes as PHC hosts, but also offers a new approach for the synthesis of these PHC hosts.

Phosphine Sulfide-Based Bipolar Host Materials for Blue Phosphorescent Organic Light-Emitting Diodes.

Three phosphine sulfide-based bipolar host materials, viz CzPhPS, DCzPhPS, and TCzPhPS, were facilely prepared through a one-pot synthesis in excellent yields. The developed hosts exhibit superior thermal stabilities with the decomposition temperatures (Td) all exceeding 350 °C and the melting temperatures (Tm) over 200 °C. In addition, their triplet energy (ET) levels are estimated to be higher than 3.0 eV, illustrating that they are applicable to serve as hosts for blue phosphorescent organic light-emitting diodes (PhOLEDs). The maxima luminance, current efficiency (CE), power efficiency (PE), and external quantum efficiency (EQE) of 17,223 cd m−2, 36.7 cd A−1, 37.5 lm W−1, and 17.5% are achieved for the blue PhOLEDs hosted by CzPhPS. The PhOLEDs based on DCzPhPS and TCzPhPS show inferior device performance than that of CzPhPS, which might be ascribed to the deteriorated charge transporting balance as the increased number of the constructed carbazole units in DCzPhPS and TCzPhPS molecules would enhance the hole-transporting ability of the devices to a large extent. Our study demonstrates that the bipolar hosts derived from phosphine sulfide have enormous potential applications in blue PhOLEDs, and the quantity of donors should be well controlled to exploit highly efficient phosphine sulfide-based hosts.

Highly efficient tandem PHOLEDs with lithium-doped BPhen/NDP-9-doped TAPC as a charge generation layer

The development of large-area organic light-emitting diode (OLED) displays requires a highly efficient tandem device architecture and an easily processable charge generation layer (CGL) with a low voltage drop and high optical transparency. In this study, we investigated and applied a doped organic n-CGL/p-CGL using thermal vacuum deposition in tandem OLED devices. A doping concentration of 1.0 wt.% for Li in 4, 7-Diphenyl-1, 10-phenanthroline (BPhen) was optimal for the n-CGL with 8 wt.% for 2-(7-dicyanomethylene-1,3,4,5,6,8,9,10-octafluoro-7H-pyrene-2-ylidene)-malononitrile (NDP-9)-doped N,N-bis(4-methylphenyl)benzenamine (TAPC) as a p-CGL. Maximum luminous efficiencies of 42.5 and 63.4 cd/A and a 4,000 cd/m2 current density for the target luminance values of 11.2 and 6.5 mA/cm2 were demonstrated for double-stack and triple-stack tandem blue phosphorescent OLED devices, respectively. Implementing these highly efficient tandem device structures will improve the overall lifetime of OLED displays by lowering their operating current density at the target luminance.

High performance blue and white phosphorescent organic light-emitting diodes obtained by sensitizing both light-emitting and electron transport layers

In this work, novel blue and white organic light-emitting diodes (OLEDs) were designed by utilizing iridium(Ⅲ)bis(4-(tert-butyl)-2,6-diuoro-2,3-bipyridinne)acetylacetonate (FK306) as sensitizer in both light-emitting and electron transport layers. Analysis of device configuration demonstrated that FK306 molecules work as electron trappers in view of their low-lying energy levels and triplet energy, which broaden the width of recombination zone, thus enhancing carriers' recombination probability and suppressing the annihilation of excitons. Consequently, blue and white devices with low turn-on voltages were reported with current efficiencies of 71.95 and 72.23 cd A−1, external quantum efficiencies of 32.62% and 31.30%, power efficiencies of 74.85 and 70.80 lm W−1 and brightness of 43171 and 37848 cd m−2, respectively. Within electron transport layer, the optimal doping concentration of FK306 is 2 wt%, which can be easily controlled in device manufacture processes. In addition, it is much more flexible in terms of sensitizer choice for doped electron transport layer compared with light-emitting layer.