Joseph C. Deaton

E-Type Delayed Fluorescence of a Phosphine-Supported Cu2(μ-NAr2)2 Diamond Core: Harvesting Singlet and Triplet Excitons in OLEDs∥

A highly emissive bis(phosphine)diarylamido dinuclear copper(I) complex (quantum yield = 57%) was shown to exhibit E-type delayed fluorescence by variable temperature emission spectroscopy and photoluminescence decay measurement of doped vapor-deposited films. The lowest energy singlet and triplet excited states were assigned as charge transfer states on the basis of theoretical calculations and the small observed S(1)-T(1) energy gap. Vapor-deposited OLEDs doped with the complex in the emissive layer gave a maximum external quantum efficiency of 16.1%, demonstrating that triplet excitons can be harvested very efficiently through the delayed fluorescence channel. The function of the emissive dopant in OLEDs was further probed by several physical methods, including electrically detected EPR, cyclic voltammetry, and photoluminescence in the presence of applied current.

High-efficiency, low-voltage phosphorescent organic light-emitting diode devices with mixed host

We report high-efficiency, low-voltage phosphorescent green and blue organic light-emitting diode (PHOLED) devices using mixed-host materials in the light-emitting layer (LEL) and various combinations of electron-injecting and electron-transporting layers. The low voltage does not rely on doping of the charge-transport layers. The mixed LEL architecture offers significantly improved efficiency and voltage compared to conventional PHOLEDs with neat hosts, in part by loosening the connection between the electrical band gap and the triplet energy. Bulk recombination in the LEL occurs within ∼10 nm of the interface with an electron-blocking layer. A “hole-blocking layer” need not have hole- or triplet-exciton-blocking properties. Optical microcavity effects on the spectrum and efficiency were used to locate the recombination zone. The effect of layer thickness on drive voltage was used to determine the voltage budget of a typical device. The behavior of undoped devices was investigated, and the electrolumines...

Highly efficient fluorescent-phosphorescent triplet-harvesting hybrid organic light-emitting diodes

We demonstrate highly efficient white and nonwhite hybrid organic light-emitting diodes (OLEDs) in which singlet and triplet excited states, generated in the recombination zone, are utilized by fluorescence and phosphorescence, respectively. The excited states are formed at a blue fluorescent light-emitting layer (LEL), and the triplets diffuse through a spacer layer to one or more phosphorescent LEL(s). A key feature enabling the triplet diffusion in such OLEDs is the use of a blue fluorescent emitter with triplet energy above, or not much below, that of the fluorescent host. Additional material properties required for triplet harvesting are outlined. At 1000 cd/m2 a blue and yellow harvesting OLED shows 13.6% external quantum efficiency, 3.8 V, 30.1 lm/W, and color characteristics suitable for display application. High-efficiency harvesting R+G+B white, and B+G and B+R nonwhite OLEDs are also demonstrated. The triplet-harvesting mechanism was verified in all devices by physical methods including spectra...

Acridinone/amine(carbazole)-based bipolar molecules: efficient hosts for fluorescent and phosphorescent emitters.

Three acridinone-based molecules ADBP, ACBP, and DABP were synthesized, and their application to the OLED devices was investigated. When used as the host for either the deep blue singlet or the green triplet emitter in OLED devices, the bipolar molecules ADBP and ACBP demonstrated superior performance compared to either DABP or commonly used host CBP, remarkably lowering the drive voltage and improving efficiencies.

P-171: High-Efficiency Low-Voltage Phosphorescent OLED Devices with Mixed Host

We demonstrate high-efficiency, low-voltage phosphorescent OLED devices (PHOLEDs) using mixed host materials in the light-emitting layer (LEL) and novel formulations in the electrontransporting/ electron-injecting layers (ETL/EIL). The LEL architecture offers significant improvement in efficiency and voltage compared to conventional phosphorescent OLEDs with carbazole-based hosts. Further voltage reduction in our PHOLEDs is achieved through use of a novel material formulation in the ETL and EIL.

Charge carriers and triplets in OLED devices studied by electrically detected electron paramagnetic resonance

Abstract— Organic light-emitting diodes (OLEDs) were investigated by an electron paramagnetic resonance (EPR) technique that uses the effective device conductance as the detection channel. This technique enables us to identify and study charge carriers and triplet excitons with high sensitivity. By using a series of model devices, it was demonstrated that this type of spectroscopy provides information regarding triplet energy transfer and the location of the recombination zone. The fundamental understanding about the extent of the recombination zone in various OLED architectures helps in the design of devices with improved performance.

17.3: Highly Efficient Fluorescent/Phosphorescent OLED Devices Using Triplet Harvesting

We demonstrate efficient white and non-white hybrid OLED devices operating by a triplet harvesting mechanism to create light. Triplet excited states are generated in a blue fluorescent light-emitting layer (LEL) and utilized upon their diffusion to the phosphorescent LEL(s). At 1000 cd/m2 a blue/yellow hybrid OLED device shows external quantum efficiency (EQE) of 13.6%, 3.8 V, 30.1 lm/W, and excellent color characteristics suitable for display application. Performance of non-white-emitting hybrids, RGB white, and a tandem hybrid device is discussed. The triplet harvesting mechanism in all hybrid devices was verified by several experimental methods (spectral analysis, time-resolved electroluminescence (EL), magnetic field effect on EL).

P‐174: Triplet Exciton Diffusion in Hybrid Fluorescent/Phosphorescent OLEDs

A hybrid OLED comprising blue fluorescent and red phosphorescent emitters is reported. External quantum efficiencies for the blue and the red components of the electroluminescence along with time-resolved measurements, magnetic field effect, and ED-EPR experiments suggest that the recombination occurs in the blue emissive layer producing fluorescence with the singlet excitons, while the triplet excitons are utilized upon migration to the red layer.

P-210: Phosphorescence Ranging from Blue to Red from tris-Cyclometalated Iridium (III) Complexes and Application to Organic Light-Emitting Devices

Color tuning in the Ir(III)-based phosphores has been accomplished by alteration of the cyclometalated ligand (C∧N). Highly efficient phosphorescence with emission peaks in the blue, green, yellowish-green, yellow, and red spectral regions has been realized and their use in organic light-emitting devices (OLEDs) is described in this paper. Efficient blue phosphorescent devices can achieve external quantum efficiencies up to 8.8% at 1 mA/cm2 with CIE coordinates of (0.14, 0.23). with the addition of one bluish-green-emitting and four red-emitting coumarin-based Ir(III) dopants to the family of the coumarin-based Ir(III) dopants reported previously, highly efficient and long-lived OLEDs, with colors ranging from green, yellowish-green, yellow, to red, have been realized. Incorporation of these coumarin-based cyclometalated Ir(III) dopants into novel tandem OLED structures gives highly efficient and stable white OLEDs.

P-178: High-Efficiency Long-Lifetime Phosphorescent OLED Devices Based on Electron-Trapping Iridium (III) Complexes

We have developed new iridium (III) complexes having coumarin, including its aza-analogue structure, in their ligands. These Ir complexes are highly emissive with colors ranging from yellow, yellowish-green to green. Electrochemical analysis shows that the reduction and oxidation potentials of these complexes occur at significantly less negative and more positive potentials, respectively, than are found for typical Ir(III) complexes in OLEDs, indicating these complexes are electron trapping instead of hole trapping. Long-lived phosphorescent OLEDs fabricated with these new Ir complexes give external quantum and power efficiencies above 18% and 33 lm/W, respectively.