High-efficiency Blue Organic Light-emitting Diodes Research Articles

Ortho-Carborane Decorated Multi-Resonance TADF Emitters: Preserving Local Excited State and High Efficiency in OLEDs.

A novel class of o-carboranyl luminophores, 2CB-BuDABNA (1) and 3CB-BuDABNA (2) is reported, in which o-carborane moieties are incorporated at the periphery of the B,N-doped multi-resonance thermally activated delayed fluorescence (MR-TADF) core. Both compounds maintain the inherent local emission characteristics of their MR-emitting core, exhibiting intense MR-TADF with high photoluminescence quantum yields in toluene and rigid states. In contrast, the presence of the dark lowest-energy charge transfer state, induced by cage rotation in THF, is suggested to be responsible for emission quenching in a polar solvent. Despite the different arrangement of the cage on the DABNA core, both 1 and 2 show red-shifted emissions compared to the parent compound BuDABNA (3). By utilizing 1 as the emitter, high-efficiency blue organic light-emitting diodes (OLEDs) are achieved with a remarkable maximum external quantum efficiency of 25%, representing the highest reported efficiency for OLEDs employing an o-carboranyl luminophore as the emitter.

High-efficiency blue-emission crystalline organic light-emitting diodes sensitized by “hot exciton” fluorescent nanoaggregates

Sensitizing fluorescent materials is an effective way to maximally use excitons and obtain high-efficiency blue organic light-emitting diodes (OLEDs). However, it is a persistent challenge for present amorphous thin-film OLEDs to improve photon emission under low driving voltage, severely impeding the development of OLED technology. Here, we propose a novel OLED architecture consisting of a crystalline host matrix (CHM) and embedded "hot exciton" nanoaggregates (HENAs), which effectively sensitize blue dopant (D) emission. Owing to the advantages of the crystalline thin-film route, the device exhibits largely enhanced blue photon output [Commission International de L'Eclairage coordinates of (0.15, 0.17)], with a low turn-on/operation voltage of 2.5 V (at 1 cd/m2)/3.3 V (at 1000 cd/m2), an extremely low Joule heat loss ratio (7.8% at 1000 cd/m2), and a maximum external quantum efficiency (EQE) up to 9.14%. These areal photon output features have outperformed the present amorphous thin-film blue OLEDs with high EQE, demonstrating that the CHM-HENA-D OLED is promising for future OLEDs.

High-Efficiency, Non-doped, Pure-Blue Fluorescent Organic Light-Emitting Diodes via Molecular Tuning Regulation of Hot Exciton Excited States.

Tremendous efforts have been made on researching triplet-triplet annihilation (TTA) and thermally activated delayed fluorescence (TADF) materials for realizing high-efficiency blue organic light-emitting diodes (OLEDs) through utilizing triplet exciton conversion to the lowest singlet excited state (S1) from the lowest triplet excited state (T1). However, hot exciton conversion from the upper triplet energy level state (Tn, n > 1) to the lowest singlet excited state (S1) is an increasingly promising method for realizing pure-blue non-doped OLEDs with performances comparable to those of TTA and TADF materials. Herein, two pure-blue fluorescent emitters of donor (D)-π-acceptor (A) type, PIAnCz and PIAnPO, were designed and synthesized. The excited-state characteristics of PIAnCz and PIAnPO, confirmed by theoretical calculations and photophysical experiments, demonstrated these materials' hot exciton properties. Based on PIAnCz and PIAnPO as emission layer materials, the fabricated non-doped devices exhibited pure-blue emission with Commission Internationale de l'Eclairage (CIE) coordinates of (0.16, 0.12) and (0.16, 0.15), maximum luminescences of 10,484 and 15,485 cd m-2, and maximum external quantum efficiencies (EQEs) of 10.9 and 8.3%. Besides, at a luminescence of 1000 cd m-2, the EQEs of PIAnPO-based devices can still be high at 7.7%, and the negligible efficiency roll-off was 6.0%. The device performance of both materials demonstrates their outstanding potential for commercial application.

Pure-Blue Fluorescence Molecule for Nondoped Electroluminescence with External Quantum Efficiency Approaching 13%

A pure-blue light-emitting material is one of the key components in the preparation of organic light-emitting diode (OLED) displays. Although high-efficiency blue OLEDs have been realized in therma...

High-efficiency blue organic light-emitting Diodes using emissive carbazole-triazine-based donor-acceptor molecules with high reverse intersystem crossing rates

Abstract We report blue thermally activated delayed fluorescent (TADF)organic light emitting diodes(OLEDs) with high efficiencies which areattributed toemployingdonor-acceptor type TADF compounds having highreverse intersystem crossing (RISC)rates. Carbazole derivatives and a triphenyltriazine (or a dibenzothiophene) are employed as the donor (D) and the acceptor (A)moieties, respectively. We can achieve four D-A type blue TADF compounds through the combination of the moieties and adjust the energy gap between the lowest excited singlet and triplet statesand accordingly the RISC rate (kRISC) for the compounds. A blue OLED using one of the TADF molecules,9-(9H-carbazol-9-yl)-12-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-5-phenyl-5,12-dihydroindolo[3,2-a]carbazole exhibitshigh maximum external quantum efficiency (22.3%)due to itsshort excitonlifetime (6.1 μs) induced by its highkRISC(1.825 × 106s−1).

Direct observations of the charge behavior of a high-efficiency blue organic light-emitting diode under operating conditions using electric-field-induced doubly resonant sum-frequency-generation vibrational spectroscopy

We investigated the carrier behavior in a high-efficiency multilayer blue organic light-emitting diode (OLED) that employs the triplet–triplet annihilation (TTA) phenomenon using electric-field-induced doubly resonant sum-frequency generation (EFI-DR-SFG) vibrational spectroscopy. We observed enhancements of the EFI-DR-SFG signals—particularly the peaks at 1404, 1464, and 1601 cm−1—when we applied forward- or reverse-bias voltages to the blue OLEDs. The results of our EFI-DR-SFG analyses of the carrier behavior in an operating blue OLED showed changes in the peak intensities at 1404 and 1464 cm−1, indicating that the electrons accumulate at the electron-blocking layer/emission layer interface. Conversely, the changes in the intensities of the peaks obtained from the hole-transport materials are caused by the cancelation of the interfacial polarization charges at the hole-injection layer/hole-transport layer interface. These results demonstrate that the EFI-DR-SFG technique is a powerful and effective tool for directly investigating the carrier behavior in practical multilayer organic devices with complicated operating mechanisms.

Trifluoromethane modification of thermally activated delayed fluorescence molecules for high-efficiency blue organic light-emitting diodes.

Highly efficient blue and green thermally activated delayed fluorescence (TADF) molecules bearing trifluoromethane-modified carbazole groups were developed. The trifluoromethane groups on carbazole induced blue-shifted emission and improved the photoluminescence quantum yield. The photostability of the TADF molecules was strongly related to the modification position of trifluoromethane on carbazole.

Suppression of efficiency roll-off in highly efficient blue phosphorescent organic light-emitting devices using novel iridium phosphors with good electron mobility

High-efficiency blue organic light-emitting diodes were reported by adopting two novel iridium phosphors. Due to phosphoryl moiety in ancillary ligands, both complexes (dfppy)2Ir(ppp) and (dfppy)2Ir(dpp) (dyppy = 2-(2,4-difluorophenyl)pyridine, ppp = phenyl(pyridin-2-yl)phosphinate, dpp = dipyridinylphosphinate) own high electron mobility which can balance the injection and transport of carriers. Furthermore, the double light-emitting layers with TcTa (4,4′,4″-tris(carbazol-9-yl)triphenylamine) and 26DCzPPy (2,6-bis(3-(carbazol-9-yl)phenyl)pyridine) hosts broaden the exciton formation zone and suppress efficiency roll-off. The optimized double light-emitting layers devices exhibited decent performances with peak current efficiency near 50 cd/A and external quantum efficiency above 20% as well as negligible efficiency roll-off.

Novel Design of Iridium Phosphors with Pyridinylphosphinate Ligands for High-Efficiency Blue Organic Light-emitting Diodes

Due to the high quantum efficiency and wide scope of emission colors, iridium (Ir) (III) complexes have been widely applied as guest materials for OLEDs (organic light-emitting diodes). Contrary to well-developed Ir(III)-based red and green phosphorescent complexes, the efficient blue emitters are rare reported. Like the development of the LED, the absence of efficient and stable blue materials hinders the widely practical application of the OLEDs. Inspired by this, we designed two novel ancillary ligands of phenyl(pyridin-2-yl)phosphinate (ppp) and dipyridinylphosphinate (dpp) for efficient blue phosphorescent iridium complexes (dfppy)2Ir(ppp) and (dfppy)2Ir(dpp) (dfppy = 2-(2,4-difluorophenyl)pyridine) with good electron transport property. The devices using the new iridium phosphors display excellent electroluminescence (EL) performances with a peak current efficiency of 58.78 cd/A, a maximum external quantum efficiency of 28.3%, a peak power efficiency of 52.74 lm/W and negligible efficiency roll-off ratios. The results demonstrated that iridium complexes with pyridinylphosphinate ligands are potential blue phosphorescent materials for OLEDs.

High-Efficiency Near Ultraviolet and Blue Organic Light-Emitting Diodes Using Star-Shaped Material as Emissive and Hosting Molecules

We have investigated the fluorescent and hosting properties of a novel star-shaped material (SSM) containing carbazole/arylamine backbone. Using SSM as an emitter, we have fabricated a near ultraviolet-emitting electroluminescent device with a peak emission at λpeak=408 nm and achieved a maximum external quantum efficiency of 2.56%. We have also demonstrated that SSM can be employed as an effective hosting material of high-efficiency blue organic light-emitting diode, in which the maximum current and power efficiencies reached 10.37 cd/A and 8.69 lm/W, respectively. We have also found that the side-band emission of blue p-bis(p-N, N-diphenyl-amino-styryl) benzene electroluminophore could be completely suppressed with the aid of SSM being hosting matrix. Hence, SSM-based blue device has a higher color-purity than 4,4'-bis(9-carbazolyl)biphenyl-based one, of which the y-value of color coordinates and the full width half maximum decreased to 0.36 from 0.45 and to 37 nm from 62 nm, respectively.

High Efficiency Blue Organic Light Emitting Devices doped by BCzVBi in Hole and Electron Transport Layer

ABSTRACTThe electroluminescent characteristics of blue organic light-emitting diodes(BOLEDs) were fabricated with single emitting layer using host-dopant system and doped charge carrier transport layers. The structure of the high efficiency BOLED device was; NPB(600Å)/NPB:BCzVBi-7%(100Å)/ADN:BCzVBi-7%(300Å)/BAlq:BCzVBi-7%(100Å)/BAlq(200Å)/Liq(20Å)/Al(1200Å) to optimize probability of exciton generation by doping BCzVBi in emitting layer and hole/electron transport layers(HTL/ETL) as well. Luminance and luminous efficiency of BOLED doped BCzVBi in EML and HTL/ETL improved from 10090 cd/m2 at 9.5V and 6.44 cd/A at 4.0V to 13190 cd/m2 at 9.5V and 7.64 cd/A at 4.0V about 30% and 18%, respectively, with CIE coordinates of (0.14, 0.17) comparing to BOLED doped BCzVBi in EML only

고효율 청색 유기발광다이오드의 DPVBi와 BCzVBi 사이에서 발생하는 흡열 페르스터 에너지전이

In this study, we demonstrated high-efficiency blue organic light-emitting diodes (OLEDs) employing BCzVBi as a blue fluorescent dye doped into blue host material, DPVBi with various concentration. The optimized blue OLED device having high-efficiency was constructed with structure of NPB (500 A) / DPVBi:BCzVBi-6% (150 A) / Alq3 (300 A) / Liq (20 A) / Al (1000 A). The maximum luminescence of blue OLED was 13200 cd/m at 13.8 V and current density and maximum efficiency were 26.4 mA/cm at 1000 cd/m and 4.24 cd/A at 3.9 V, respectively. Luminous efficiency shows two times higher than comparing with non-doped BCzVBi blue OLED whereas CIEx,y coordinate was similar with bare DPVBi blue OLED such as (0.16, 0.19). Electroluminescence of BCzVBi-6% doped blue OLED has two major peaks at 445 nm and 470 nm whereas pure DPVBi’s blue peak appears at 456 nm and it is happened through endothermic Forster energy transfer by molecule's vibration between LUMO of DPVBi as host material and LUMO of BCzVBi as dopant in device.

High-Efficiency Blue Organic Light-Emitting Diodes Using C[sub 60] as a Surface Modifier on Indium Tin Oxide

C 60 was introduced as a modifier on indium tin oxide (ITO) and the effect of C 60 modification on light-emitting efficiency of blue organic light-emitting didoes was investigated. Device performances of C 60 modified devices were greatly dependent on ITO surface properties and C 60 thickness. Power efficiency of blue devices was improved by 80% by C 60 buffer layer on ITO because of low driving voltage and balanced electron-hole recombination.