Viktor V. Jarikov

Studies of the degradation mechanism of organic light-emitting diodes based on tris(8-quinolinolate)aluminum Alq and 2-tert-butyl-9,10-di(2-naphthyl)anthracene TBADN

Previously, radical cation of tris(8-quinolinolate)aluminum (Alq•+) has been associated with the instability of Alq films subjected to holes-only electrical current. Yet, the questions remain (i) whether Alq•+ is the primary source of the intrinsic degradation of bipolar organic light-emitting diodes (OLEDs) based on Alq, (ii) whether Alq•+ reactions result in deep charge traps in holes-only devices as found in bipolar counterparts, and (iii) whether radical cations can be a common source of degradation of OLEDs irrespective of materials. With regards to generality of hole-current-related degradation, it is interesting to examine the behavior of 9,10-diarylanthracenes (DAAs)—the practically important class of blue-fluorescing light-emitting-layer hosts. These questions prompted our comparative study of the effects of unipolar currents in Alq and 2-t-butyl-9,10-di(2-naphthyl)anthracene (TBADN), which was chosen as a representative material of the DAA class. First, we identified device structures allowing f...

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...

Quantum efficiency improvement in anthracene-based organic light-emitting diodes codoped with a hole-trapping material

We focus on organic light-emitting diodes having an N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine (NPB) hole-transport layer, a doped light-emitting layer (LEL) based on a 9,10-diarylanthracene (DAA), and a tris(8-quinolinolato)aluminum (Alq) electron-transport layer. The addition of a hole-trapping codopant, e.g., NPB, to the LEL can triple the external quantum efficiency (EQE), which can reach 3%–6%. We discuss (a) the magnitude of the effect and the causes, (b) the effect on the drive voltage, emission spectrum, and operating lifetime, and (c) the approaches to higher EQEs of 5%–10%. We compare (a) various blue and green LEL dopants, (b) NPB codopant with aminated polycyclic aromatic hydrocarbons, which reduce the EQE, and (c) the DAA-based cells with their Alq-based counterparts.

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 ...

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.

Tris­(quinolin-8-olato)­indium(III)

The single-crystal structure of the title compound, [In(C9H6NO)3], is described. Quinolinolates of the elements of the group IIIB (denoted by MQ3), Al, Ga, and In, have been of continuous interest to organometallic and physical chemists, in particular, for the last 50 years. Organic light-emitting diodes (OLEDs) utilizing GaQ3 and InQ3, the gallium and indium analogs, respectively, of the most widely used OLED material AlQ3, were first explored in the early 1980s and continue to be the subject of current research. To the best of our knowledge, the structure reported here is the first-ever facial MQ3-type structure, confirmed by single-crystal X-ray crystallography.

P‐148: Temperature Dependence of Degradation in Organic Light‐Emitting Diodes

Prolonged operation of an OLED degrades the luminance and alters the voltage-dependent capacitance. The loss of luminance in simple blue and green fluorescent OLEDs is linearly correlated with internal charge accumulation at the HTL|LEL interface. The shapes of the EL decay curve and the transition-voltage-rise curve are independent of temperature. Proper scaling of the time axis makes plots of EL or transition voltage vs. time at different temperatures to coincide. The resulting universal decay curves are not altered by the introduction of the fluorescent dopant, suggesting that the degradation processes are the same in the doped and undoped devices. Red fluorescent OLEDs of more complicated structure degrade in a dopant-dependent manner.