Christopher T. Brown

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...

Efficient and extremely long-lived organic light-emitting diodes based on dinaphthylperylene

We describe a synergistic effect of a lifetime-extending light-emitting-layer (LEL) additive and improved electron injection and transport in organic light-emitting diodes (OLEDs). Previously reported di(2-naphthyl)perylene (DNP) serves as the LEL additive capable of extending the operating lifetime of OLEDs by over two orders of magnitude. Using 2-phenyl-9,10-di(2-naphthyl)anthracene (PADN) as an electron-transport layer (ETL) and a separate layer of 4,7-diphenyl-1,10-phenanthroline (BPhen) as an electron-injection layer (EIL) significantly improves electron delivery into the charge recombination zone relative to traditional ETL made of tris(8-quinolinolate)aluminum (Alq). This ETL∣EIL combination not only results in approximately seven times lower electric field in the ETL and, thus, lower drive voltage and higher efficiency devices, but can also increase device lifetime substantially. In a representative device containing a red-emitting LEL dopant [Commission Internationale de l’Eclairage 1931 2° color...

Chemical reactivity of aromatic hydrocarbons and operational degradation of organic light-emitting diodes

We report the study of the chemical reactivity of representative hydrocarbon organic light-emitting diode (OLED) materials—fully aromatic derivatives of anthracene and tetracene in the OLED environment. In addition to the participation in free-radical chemistry initiated by homolytic bond dissociation reactions of arylamines, the hydrocarbons appear to initiate and undergo dehydrogenation reactions following the electronic excitation caused by the recombination of charge carriers or by the absorption of a photon. A chemical product of the intramolecular dehydrogenation reaction, cyclization, was identified in photoexcited films of representative anthracene derivative and detected in electrically degraded OLEDs utilizing this material in the emissive layer. Other analogous intra- and intermolecular dehydrogenation reactions initiated by the excited states of hydrocarbons are also expected to occur in operating OLEDs. The stepwise transfers of hydrogen atoms or ions to neighboring molecules are likely to yi...

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.

A RIGID CYTIDINE-RUII(BPY)3 CONJUGATE. A POTENTIAL PRECURSOR FOR NON-COVALENT ELECTRON TRANSFER MODELING

The synthesis and characterization of the first cytidine substituted ruthenium(II) trisbipyridine complex, Ru((4″,4‴-ethynyl-5(4-amino-1- (2⁗,3⁗,5⁗-tris-(Otert-butyldimethylsilyl-β-D-ribofuranosyl))pyrimidin-2-one-2″,2‴- bipyridyl)-2,2′-bipyridyl)22+ (1), is reported. This complex, which is characterized by UV-Vis absorption bands at 484 and 368 nm, an emission band at 655 nm, and reduction/oxidation waves at −1.0, −1.4, −1.7 and 1.4 V versus Ag/AgCl, could serve as a new photodonor and/or acceptor for use in the construction of redox-active, non-covalent electron transfer model systems.

Intracomplex electron transfer in a hydrogen-bonded calixarene–porphyrin system

Photoinduced electron transfer in a non-covalent assembly based on supramolecular contacts between the phenolic hydroxy groups of a calix[4]arene-substituted ZnII metalloporphyrin photodonor and the carbonyl groups of a benzoquinone acceptor (Ka= 40 ± 3.6 dm3 mol–1) in CDCl3 occurs with a rate constant of (8.0 ± 0.2)× 108 s–1.

Operating lifetime recovery in organic light-emitting diodes having an azaaromatic hole-blocking/electron-transporting layer

Azaaromatic compounds (AACs) are widely used in organic light-emitting diodes (OLEDs), especially as efficient electron transporters. Yet, the operating lifetime of OLEDs is always compromised when AACs are involved in anything more than electron transport (e.g., hole blocking). We show (i) the operating lifetime of OLEDs incorporating AACs as a hole-blocking/electron-transporting layer (HBETL) depends strongly on the charge-conducting ability and excited state energy of the light-emitting layer (LEL) materials and (ii) shifting the charge recombination zone away from the LEL∣HBETL interface deeper into the LEL can recover the lost lifetime. Thus, a pure red fluorescent OLED is demonstrated having 5.3 V drive voltage, 6.5% external quantum efficiency, 6.6 cd/A electroluminescent yield, and ∼125 000 h half-life, all at 20 mA/cm2. This device utilizes an AAC as HBETL followed by an aluminum triquinolate (Alq) ETL doped with Li metal. Alternatively, the lifetime recovery might be assigned to the presence of ...

5.2: Probing Chemical Instability of Aromatic Hydrocarbons in Operating OLEDs

We show that representative hydrocarbon materials fully aromatic derivatives of anthracene and tetracene undergo significant chemical transformation in operating OLEDs and model structures. The electronic excitation appears to initiate dehydrogenation reactions, foliowed by hydrogen transfer to neighboring molecules and sub sequent formation of performance damaging species—nonradiative recombination centers and luminescence quenchers.

P-169: Efficient, Long-Lifetime OLED Host and Dopant Formulations for Full-Color Displays

We report developments in materials and formulations for blue, green, and red fluorescent OLEDs that provide lifetimes exceeding 15,000 h for a model display operating at 200 cd/m2 with a polarizer. In addition, we describe improvements in electron transport and injection that result in a reduction in display power consumption of up to 55%.

30.2: Improving Operating Lifetime of Organic Light‐Emitting Diodes with Perylene and Derivatives as Aggregating Light‐Emitting‐Layer Additives

Aggregating PAHs of the perylene class are useful as LEL additives. They greatly improve the device operating half-life up to 1,000,000 h at the initial luminance of 1540 cd/m2 (20 mA/cm2). There appear to be at least three factors in the lifetime increase: takeover of the LEL functions by the PAHs, aggregation, and an expansion of the recombination and/or emission zone.