Red Phosphorescent Organic Light Research Articles

Rivers of Light—Ternary Exciplex Blends for High Efficiency Solution‐Processed Red Phosphorescent Organic Light Emitting Diodes

AbstractRed‐emitting organic light‐emitting diodes (OLEDs) are important for displays and lighting, with the latter benefiting from solution processable materials, which would enable low embedded energy, scalable fabrication. Herein, the effect of annealing and phase separation on the performance of solution‐processed OLEDs incorporating a light‐emitting layer composed of the exciplex host, m‐MTDATA:OXD‐7, and a red phosphorescent light‐emitting dendrimer, Ir(tDCpq)3, is described. Solution‐processed OLEDs containing an annealed emissive layer with a low dendrimer concentration (2 wt%) are found to have the best performance, which is higher than the device in which the light‐emitting layer is not annealed. The improvement in the performance of the annealed device is ascribed to improved charge mobility within the emissive layer caused by phase separation of the OXD‐7. The OLEDs containing annealed m‐MTDATA:OXD‐7:(2 wt%) Ir(tDCpq)3 have maximum current, power, and external quantum efficiencies of 17.9 cd A−1, 19.4 lm W−1, and 14.8 ± 0.6%, respectively. The fact that the maximum external quantum efficiency (EQE) of 14.8% is larger than that expected based on the photoluminescence quantum yield (PLQY) and the normal out‐coupling efficiency of 20% from a bottom‐emitting device is determined to arise from the different pathways of exciton formation under photoexcitation and charge injection.

Novel benzothiadiazine 1,1-dioxide based bipolar host materials for efficient red phosphorescent organic light emitting diodes

Abstract In this work, three novel bipolar host materials TPA-SA, 3CBZ-SA and 4CBZ-SA have been designed and synthesized by incorporating triphenyl amine and carbazole as donor and benzothiadiazine 1,1-dioxide as an acceptor. These molecules exhibit moderately high triplet energies and bipolar carrier transport characteristics (ambipolarity) which is useful for the exothermic energy transfer to the dopants and also for the balanced carrier injection/transport in the emissive layers. These materials exhibited good performances in PhOLEDs and furnished external quantum efficiency in the range of 10.0–15.0%. Notably, a red phosphorescent device using TPA-SA as the host doped with Ir(pq)2(acac) exhibited a maximum EQE, power efficiency and current efficiency of 15.0%, 16.0 lm/W, and 25.3 cd A−1, respectively.

3,3′-Bicarbazole-based compounds as bipolar hosts for green and red phosphorescent organic light-emitting devices

Two 3,3‘-bicarbazole derivatives, with triphenylsilyl and toluenesulfonyl moieties attached to 9,9‘-positions were synthesized and their properties were studied. The compounds exhibited high triplet energies of 2.9 eV which made them useful for efficient triplet exciton harvesting. The compound containing triphenylsilyl moieties was found to have bipolar charge-transporting properties which makes it a good candidate for employment as a host in phosphorescent organic light emitting diodes. A series of green and red devices with the newly synthesized host and phosphorescent emitters were fabricated and the performance of the hist was compared with that of 1,3-bis(N-carbazolyl)benzene (mCP). Triphenylsilyl-substituted 3,3‘-bicarbazole was found to be competitive host with the widely used host mCP. Green and red phosphorescent organic light emitting diodes containing this host showed maximum external quantum efficiencies of 13.8 and 7.7%, respectively.

Solution-Processable Csp3-Annulated Hosts for High-Efficiency Deep Red Phosphorescent OLEDs.

In this report, a solution-processable cohost system incorporating N,N'-di(naphtalene-1-yl)-N,N'-diphenylbenzidine (NPB) and Csp3-annulated phenylquinoline derivatives, including spiro[indeno[1,2-b]quinoline-11,8'-indolo[3,2,1-de]acridine] (IAIQ), 10-phenyl-10H-spiro[acridine-9,11'-indeno[1,2-b]quinoline] (PAIQ) and 3,3'-(11H-indeno[1,2-b]quinoline-11,11-diyl)bis(N-phenyl-N-(m-tolyl)aniline) (m-TPA-DPIQ), is developed for highly efficient saturated red phosphorescent organic light emitting diodes (OLEDs). IAIQ, PAIQ, and m-TPA-DPIQ, designed with the increase of molecular flexibility, are systematically investigated. Solution-processable devices based on the efficient phosphorescent emitter bis[2-(3,5-dimethylphenyl)isoquinolinato](2,8-dimethyl-4,6-nonanedionato)Iridium [Ir(mpiq)2divm] are successfully fabricated, and give electroluminescent peaks at 634-636 nm with Commission Internationale de L'Eclairage coordinates of (0.70, 0.30). Under optimized conditions, the devices incorporating IAIQ, PAIQ, and m-TPA-DPIQ exhibit high external quantum efficiency with the maximum value at 25.1%, 23.4%, and 23.3%, respectively, and all exceeding 18% at the luminance of 1000 cd/m2. In application, the supersaturated red devices with excellent performance could facilitate the development of wet-made displays. The newly developed Csp3-annulated host materials with their excitonic properties also showoff the tactic to construct cohost system for high-quality phosphorescent OLEDs.

Efficient donor-acceptor emitter based nonsymmetrical connection for organic emitting diodes with improving exciton utilization.

A new strategy developed to construct blue emissive materials having an unsymmetrical connection with identical conjugated phenanthrimidazole groups results in the separation of the frontier orbitals and leads to donor–acceptor (D–A) architecture. The blue device with 2-(naphthalen-1-yl)-1-(4-(1-(naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenyl)-1H-phenanthro[9,10-d]imidazole (p-PPI)/2-(naphthalen-1-yl)-1-(3-(1-(naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenyl)-1H-phenanthro[9,10-d]imidazole (m-PPI) emissive layer (λEL – 434/420 nm) shows high efficiencies: current efficiency (ηc) – 5.83/3.56 cd A−1; power efficiency (ηp) – 5.73/3.48 lm W−1; external quantum efficiency (ηex) – 8.98/6.48% at 3.0 V. Their cyano derivatives, p-CNPPI/m-CNPPI (λEL – 422/406 nm) exhibit maximum efficiencies (ηc – 6.28/4.38 cd A−1; ηp – 6.14/4.01 lm W−1; ηex – 9.01/6.72%) at 2.9 V compared to the p-PPI/m-PPI devices. The weak charge transfer in the D–A emitters results in deep blue emission. The anisotropic structural characteristics of p-PPI, p-CNPPI, m-PPI and m-CNPPI induced horizontal dipole orientation in films and enhanced EL efficiency. These bipolar materials with suitable triplet energy can be used as hosts in green as well as red phosphorescent organic light emitting devices (PHOLEDs). The green/red device (λEL – 504/618 nm) with p-CNPPI: Ir(ppy)3/Ir(MDQ)2 (acac) exhibits a maximum L – 8823/38418 cd m−2; ηex – 24.56/17.31%; ηc – 84.30/18.09 cd A −1; ηp – 86.43/21.43 lm W −1with CIE (0.33, 0.61)/(0.65, 0.34).

Efficient red phosphorescent OLEDs based on the energy transfer from interface exciplex: the critical role of constituting molecules

A novel acceptor material, 9-(4′-(4,6-diphenyl-1,3,5-triazin-2-yl)-[1,1′-biphenyl]-3-yl)-9H-carbazole (o-DTPPC) was developed to form interface exciplex with commonly used donors, to maximize the performances of red phosphorescent organic light emitting diodes (PHOLEDs). It is found that the exciplex involving 4,4′-(cyclohexane-1,1-diyl)bis(N,N-di-p-tolylaniline) (TAPC) exhibits the most significant thermally activated delayed fluorescence (TADF) property, derived from the high triplet energy level as well as strong hole-transporting ability of TAPC. Intriguingly, it is the same donor-acceptor combination which achieved the highest device efficiency when adopted as the host for red PHOLEDs. Maximum efficiencies as high as 31.36 cd A−1,17.95 lm W−1, and 21.01% for the current efficiency, power efficiency and external quantum efficiency, respectively with low efficiency roll-off were realized. The improved performance can be attributed to the efficient TADF properties of the interface exciplex-forming host constituting TAPC, benefiting the Forster energy transfer. The article first underlines the importance of the constituting molecules in the interface exciplex-forming hosts, shedding new insight about the choice of interface exciplex as the host for PHOLEDs, which may lead to even higher performances, paving their ways towards practical applications.

Three Times Lifetime Improvement of Red-Emitting Organic Light-Emitting Diodes Based on Bipolar Host Material

A novel bipolar material 3-phenyl-10-(4-phenylquinazolin-2-yl)-3,10-dihydropyrrolo[3,2-a]carbazole (PQCz) was successfully designed and synthesized as the host material for red phosphorescent organic light emitting diodes (PhOLEDs). In this compound carbazole derivative as the donor unit and phenylquinazolin derivative as the acceptor unit. A red electroluminescent device based on this new host material is able to achieve 23.65 cd/A current efficiency and relatively flat efficiency roll-off. The operational lifetime of the devices were monitored with an initial luminance of 1000 cd/m2 under constant currents at room temperature. The device hosted by PQCz exhibit longer lifetimes (LT95) of more than 1500 h, which is about three times longer than that in the control device using CBP as host (500 h), which is the most longest operational lifetime red PhOLED reported to date to our knowledge.

Synthesis, physical and electroluminescent properties of [1,2,4]-triazolo[4,3-a]-pyridine based bipolar red host materials and their applications in organic light-emitting diodes

[1,2,4]-Triazolo[4,3-a]-pyridine based bipolar red host materials, tris(4-([1,2,4]triazolo[4,3-a]pyridin-3-yl)phenyl)amine (TPATP) and tris(4′-([1,2,4]triazolo[4,3-a]pyridin-3-yl)biphenyl-4-yl)amine (TPAPTP) were synthesized for use in red phosphorescent organic light emitting diodes (PhOLEDs). [1,2,4]triazolo[4,3-a]pyridine enhances the electron transport, while the triphenylamine derivatives enhances the hole transport. Bipolar host materials were prepared by the combination of electron and hole transporting materials. The TPATP and TPAPTP have high triplet energy and appropriate HOMO and LUMO energy levels for charge transportation. Red PhOLED devices based on TPATP and TPAPTP as host materials and Ir(piq)2acac as dopant was fabricated, which showed electroluminescent performance with a maximum external quantum efficiencies of 6.04% for TPATP and 9.1% for TPAPTP, maximum power efficiency of 3.71cd/A for TPATP and 5.58cd/A for TPAPTP, and maximum luminance of 3.54cd/m2 for TPATP and 5.3cd/m2 for TPAPTP were obtained.

Efficient red phosphorescent organic light emitting diodes based on solution processed all-inorganic cesium lead halide perovskite as hole transporting layer

Abstract An efficient red phosphorescent organic light emitting diode (PhOLED) has been realized by utilizing a composite hole transporting layer comprised of all-inorganic cesium lead halide perovskite CsPbBr 3 via spin-coating and 1,3-bis(9-carbazolyl) benzene (mCP) by vacuum depositing, in which CsPbBr 3 film is used as a hole transporting layer and mCP plays a dominant role in electron and exciton blocking. And this PhOLED shows a saturated red emission coordinated at CIE (0.65, 0.33) driven at 7.5 V, a maximum brightness of 20,750 cd/m 2 , and a maximum current efficiency of 10.64 cd/A, which is as 1.87 times as that 5.68 cd/A of the reference PhOLEDs based on traditional small organic molecular hole transporting material N , N ′-bis(naphthalen-1-yl)- N , N ′-bis(phenyl)-benzi (NPB). The electroluminescent (EL) spectra and the energy level alignment of different PhOLEDs are investigated. The enhanced EL performances are ascribed to improved hole injecting and transporting behaviors, and better electron and exciton confinements by introducing the composite hole transporting layer CsPbBr 3 /mCP.

Thieno[3,4-c]pyrrole-4,6-dione as novel building block for host materials for red PhOLEDs

Thieno[3,4-c]pyrrole-4,6-dione has been applied as novel building block for host materials for red phosphorescent organic light emitting diodes.

Solution processed multilayer red, green and blue phosphorescent organic light emitting diodes using carbazole dendrimer as a host

4, 4'-bis(3,6-bis(3, 6-ditert-pentyl-carbazol-9-yl)carbazol-9-yl)-2,2'-dimethylbiphenyl, a novel carbazole dendrimer, has been synthesized. This compound shows an excellent thermal stability with a high glass transition temperature of 283°C and decomposition temperature of 487°C. Density functional theory is used to investigate the frontier orbitals. It was found that the Highest Occupied Molecular Orbital and the Lowest Unoccupied Molecular Orbital levels of 4, 4'-bis(3,6-bis(3, 6-ditert-pentyl-carbazol-9-yl)carbazol-9-yl)-2,2'-dimethylbiphenyl are nearly degenerate to the next highest or lowest frontier orbitals. The electron rich outer dendrons along with Highest Occupied Molecular Orbital level of 5.24eV as determined from cyclic voltammetry makes 4, 4'-bis(3,6-bis(3,6-ditert-pentyl-carbazol-9-yl)carbazol-9-yl)-2,2'-dimethylbiphenyl a good hole transporting material. This compound also shows a triplet energy of 2.83eV. Solution processable multilayer red, green and blue phosphorescent organic light emitting diodes are fabricated having 4, 4'-bis(3,6-bis(3,6-ditert-pentyl-carbazol-9-yl)carbazol-9-yl)-2,2'-dimethylbiphenyl as a hole transporting host. It was found that the CIE-coordinates remain constant within a wide range of brightness.

Effect of mixed hole transporting host on the mobility, Gaussian density of states and efficiencies of a heterojunction phosphorescent organic light emitting diode

We present an in-depth study of the hole transport in poly(vinylcarbazole) PVK films blended with small molecule tris(4-carbazoyl-9-ylphenyl)amine (TcTa). Doping TcTa in PVK introduces shallow hole traps when the doping concentration is lower than 20 wt%. It becomes percolative at higher concentrations. The energetic disorder σ of the blended system reduces from ~72 meV at 0 wt% TcTa to ~41 meV at 50 wt% TcTa. A correlation between σ and the film morphologies suggests that the blending of TcTa molecules in the film does not only change the film homogeneity and roughness but also the energetic disorder. In addition to the mobility study, we fabricated a red phosphorescent organic light emitting diode with the same blending system. By doping merely 5 wt% of TcTa into PVK as mixed hole-transporting hosts, the efficiency of the deep red heterojunction phosphorescent organic light emitting diode increased from 2 cd A−1 to 4 cd A−1, suggesting that TcTa molecules assist in hole injection.

Green and red phosphorescent organic light-emitting diodes with ambipolar hosts based on phenothiazine and carbazole moieties: photoelectrical properties, morphology and efficiency

The two low-molar mass compounds based on phenothiazine and carbazole moieties were synthesized and investigated as the ambipolar hosts for the green and red phosphorescent organic light emitting diodes.

Highly efficient organic light emitting diodes formed by solution processed red emitters with evaporated blue common layer structure.

We prepared highly-efficient solution-processed red phosphorescent organic light emitting diodes (PHOLEDs) with a blue common layer structure that can reasonably confine the triplet excitons inside of the red emission layer (EML) with the assistance of a bipolar exciton blocking layer. The red PHOLEDs containing EML with a 7 : 3 ratio of 11-(4,6-diphenyl-[1,3,5]triazin-2-yl)-12-phenyl-11,12-dihydro-11,12-diaza-indeno[2,1-a]fluorene (n-type host, NH) : 4-(3-(triphenylen-2-yl)phenyl)dibenzo[b,d]thiophene (p-type host, PH) doped with 5% Iridium(III) bis(2-(3,5-dimethylphenyl)quinolinato-N,C2’)tetramethylheptadionate (Red Dopant, RD) produced the highest current and power efficiencies at 23.4 cd/A and 13.6 lm/W, with a 19% external quantum efficiency at 1000 cd/m2. To the best of our knowledge, such efficiency was the best among those that have been obtained from solution-processed small molecular red PHOLEDs. In addition, the host molecules utilized in this study have no flexible spacers, such as an alkyl chain, which normally deteriorate the stability of the device.

Improved Performance of Red Phosphorescent Organic Light Emitting Diodes Using Partial Mixed Host System.

Phosphorescent organic light-emitting diodes (PHOLEDs) have shown a heterojunction system that is a bulk heterojunctioned emitting layer (EML). In our work, we have demonstrated an improvement in efficiency with a partial mixed host system in an EML. A mixed host system, which is mixed with a host material and an electron transporting material, was used on the red PHOLEDs. In general, the recombination zone is located at the electron transporting layer (ETL) side in typical PHOLEDs due to excessive accumulation at the interface. However, this study proposed the removal of interfaces through the advantage of a mixed host system and a mixed layer between EML and ETL sides to increase the electron mobility of the experiments. Detailed optical and electrical analysis of these phenomena, were demonstrated.

Efficient and stable red organic light emitting devices from a tetradentate cyclometalated platinum complex

An efficient and stable red phosphorescent organic light emitting diode was developed using a tetradentate cyclometalated platinum complex. Devices employing the phosphorescent molecule, platinum(II)-9-(4-methylpyridin-2-yl)-2-(3-(quinolin-2-yl)phenoxy)-9H-carbazole (PtON11Me), yielded high external quantum efficiencies and high operational lifetimes. A maximum EQE of 12.5% and color coordinates CIE (x=0.61, y=0.36) was achieved in devices employing efficient hole blocking and transporting materials and a high operational lifetime of T0.97∼3200h was achieved in devices utilizing electrochemically stable hole blocking and transporting materials.

Improved Light Outcoupling from OLED by Non-Wave-Guiding Anode Designs

ABSTRACTWe improve the efficiency of a bottom-emitting red phosphorescent organic light emitting diode (OLED) by the suppression of wave-guided modes in the bottom contact. ITO as bottom contact layer has been substituted by a thin Ti/Au layer. Electromagnetic simulation results of both devices predict the absence of TE polarized guided contact modes by the use of 10 nm Au as bottom electrode. We measured an improved outcoupling of light which overcompensates absorption losses of the Ti/Au layer in the measured emission cone. By the use of 1 nm Ti as undercoat, a continuous Au film of 8 nm thickness could be realized with an improved transmittance for long wavelengths (λ > 550 nm). As a consequence of fewer lateral guided modes, the external quantum efficiency (EQE) has been enhanced from 11.5 % of the standard device to 14 % of the device with the Ti/Au electrode.

TCTA对红绿磷光有机电致发光器件发光层激子的调控作用

Red and green phosphorescent organic light emitting diodes were fabricated,utilizing GIr1 and R-4B(novel red and green) phosphorescent materials.Device structure was ITO/MoO3(50 nm)/NPB(40 nm)/TCTA(10 nm)/CBP∶14%GIr1(30 nm)/TCTA(x)/CBP∶2%R-4B(10 nm)/BCP(10 nm)/Alq3(40 nm)/LiF(1 nm)/ Al(100 nm).The luminescent properties were studied by inserting different thickness of TCTA(regulation of carrier) spacer layer between red and green emitting layer to adjust the distribution of carriers and excitons.The results showed that the optimum performance of OLED was achieved when the thickness of TCTA spacer layer is 1 nm.The maximum the device performance reached 13.72 cd/A,0.509 mA/cm2 and 69.91 cd/m2 at 6 V.While for 0 nm(none spacer),the device performance reached 11.67 cd/A,1.848 mA/cm2 and 215.7 cd/m2 at 6 V.

Improving the efficiency of red phosphorescent organic light emitting diodes by exciton management

AbstractPhosphorescent organic light emitting diodes (PHOLEDs) have undergone remarkable development from both academia and industry in the past decade. Nevertheless, devices with higher efficiency remain highly desirable for energy‐efficient general lighting as well as low power consumption LED backlight applications. In this respect, several groups have conducted complex device engineering designs such as doping of the transport layers to increase charge carrier mobility, incorporation of blocking layers to confine excitons/charge carriers, or use of multiple emissive layers to widen the emission zone, in order to achieve higher device performances. In this work, we report an alternative and relatively simple approach to improve the efficiency of red PHOLEDs by exciton management to attain a high external quantum efficiency (EQE) of >20%. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Chemical degradation processes of highly stable red phosphorescent organic light emitting diodes

We investigate the chemical degradation processes of highly stable red organic light emitting diodes (OLEDs) based on the triplet emitter tris(1-phenylisoquinoline)iridium(III) by laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF-MS). The analysis of LDI-TOF spectra, collected on OLEDs driven at different current densities, shows a direct correlation between the lifetime of the devices and the formation of the three different reaction products: a BPhen dimer, an adduct of BPhen dimer with cesium, and the complex [BAlq2+Al(Me-q)2]+ as well. Additionally it was possible to identify another degradation product, whose chemical structure is related to the α-NPD molecule as well to the fluorine of the used p-dopant. This product is only observable in devices aged at very high current densities.