This article provides a review about electroluminescence from organic materials and deals in detail with organic light-emitting diodes (OLEDs), light-emitting electro-chemical cells (LECs) and electrogenerated chemilumi-nescence (ECL) reflecting different electrooptical appli-cations of conjugated materials. It is written from an organic chemist's point of view and pays particular attention to the development of organic materials involved in corresponding devices. In recent years a substantial amount of both academic and industrial research has been directed to organic electroluminescence in an effort to improve the processability and tunability of organic materials and the longevity of OLEDs and LECs. On the eve of the commercialization of organic electrolumi-nescence this review provides an overview of lifetimes and efficiencies attained and reflects materials and device concepts developed over the last decade. In this context electrogenerated chemiluminescence is discussed with respect to its importance as a versatile tool to simulate the fundamental electrochemical processes in OLEDs.

The electroluminescence of organic materials

A comprehensive review of the literature on electron transport materials (ETMs) used to enhance the performance of organic light-emitting diodes (OLEDs) is presented. The structure−property−performance relationships of many classes of ETMs, both small-molecule- and polymer-based, that have been widely used to improve OLED performance through control of charge injection, transport, and recombination are highlighted. The molecular architecture, electronic structure (electron affinity and ionization potential), thin film processing, thermal stability, morphology, and electron mobility of diverse organic ETMs are discussed and related to their effectiveness in improving OLED performance (efficiency, brightness, and drive voltage). Some issues relating to the experimental procedures for the estimation of relevant material properties such as electron affinity and electron mobility are discussed. The design of multifunctional electroluminescent polymers whereby light emission and electron- and hole-transport pro...

Electron Transport Materials for Organic Light-Emitting Diodes

Provided is an organic electroluminescence device having high luminous efficiency, high heat resistance and an extremely long lifetime. The organic electroluminescence device of the present invention includes an organic thin film layer composed of one or more layers containing at least a light emitting layer is interposed between a cathode and an anode. The light emitting layer includes a compound containing a condensed ring and a luminescent metal complex capable of emitting light having a red-based color. It is preferable that the compound containing a condensed ring includes a host material, while the luminescent metal complex capable of emitting light having a red-based color includes a phosphorescent dopant.

Organic Electroluminescent Device

One of the requirements for efficient organic electroluminescent devices (OLEDs) is balanced charge injection from the two electrodes and efficient transport of both holes and electrons within the luminescent layer in the device structure. Many of the common luminescent conjugated polymers, e.g. derivatives of poly(phenylenevinylene) and poly(fluorene), are predominantly hole transporters (i.e. p-dopable). This article gives a brief overview of organic electroluminescence and electrophosphorescence and provides a more detailed consideration of ways in which electron transport in these systems has been enhanced by the incorporation of electron-deficient (i.e. n-dopable) small molecules and polymers into the devices, either as blends or by covalent attachment of sub-units to the luminophore or as an additional electron-transporting, hole-blocking (ETHB) layer adjacent to the cathode. The chemical structures of these systems are presented and their roles are assessed. Most of these ETHB molecules are electron-deficient aromatic nitrogen-containing heterocycles, e.g. derivatives of 1,3,4-oxadiazole, pyridine, pyrimidine, pyrazine, quinoline, etc. Non-aromatic thiophene-S,S-dioxide derivatives are also discussed. The article is written from an organic chemist's perspective.

Electron-transporting materials for organic electroluminescent and electrophosphorescent devices

Electrophosphorescent devices with fac-tris(2-phenylpyridine)iridium as the green emitting dopant have been fabricated with a variety of hole and exciton blocking materials. A device with aluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate (BAlq) demonstrates an efficiency of 19 cd/A with a projected operational lifetime of 10 000 h, operated at an initial brightness of 500 cd/m2; or 50 000 h normalized to 100 cd/m2. An orange-red electrophosphorescent device with iridium(III) bis(2-phenylquinolyl-N,C2′)acetylacetonate as the dopant emitter and BAlq as the hole blocker demonstrates a maximum efficiency of 17.6 cd/A with a projected operational lifetime of 5000 h at an initial brightness of 300 cd/m2; or 15 000 h normalized to 100 cd/m2. The average voltage increase for both devices is <0.3 mV/h. The device operational lifetime is found to be inversely proportional to the initial brightness, typical of fluorescent organic light emitting devices.

High operational stability of electrophosphorescent devices

A series of low molecular weight dimeric 1,3,5-triazine ethers with high glass transition temperatures is synthesized from 2-(4-fluorophenyl)-4,6-diphenyl-1,3,5-triazine and various bisphenols. The thermal and electrochemical properties of these materials are examined using differential scanning calorimetry and cyclic voltammetry, respectively. The glass transition temperatures (Tg) are in the range of 106−144 °C, and all of them have similar thermal stability and show no weight loss up to 380 °C in thermogravimetric measurements. Some of these dimers form stable glasses which do not recrystallize on annealing at or above the Tg. Cyclic voltammetry studies reveal that these compounds undergo reversible reduction between −2.09 and −2.27 V vs ferrocene/ferrocenium as internal standard which correspond to LUMO values between −2.5 and −2.7 eV, respectively. The application of one of these dimeric ethers as a hole-blocking/electron-transport material in organic light-emitting devices is demonstrated.

Synthesis and Application of Dimeric 1,3,5-Triazine Ethers as Hole-Blocking Materials in Electroluminescent Devices

A key for the understanding of the electronic properties of organic light-emitting devices (OLEDs) is the frequency dependent investigation of their complex resistance. We report impedance spectroscopy measurements of electroluminescent (EL) single-layer and double-layer systems. It is shown that there are important differences found in the corresponding equivalent electrical circuits. In EL single-layer devices the electrical field decreases homogeneously over the entire layer thickness, resulting in an equivalent circuit of one RC component. In contrast, for the EL two-layer devices two RC components are necessary for the description. In both systems no indications of an insulating layer or a depletion region are found. During the measurements of the impedances of operated EL single-layer and EL two-layer systems, both under inert gas and in air, an increase of the resistance is observed. However, there are no signs for an insulating layer covering the entire contact area, through which the transport of...

Investigation of the Electronic Properties of Organic Light-Emitting Devices by Impedance Spectroscopy

Electroluminescent arrangement of two or more electrodes and a light-emitting layer system including one or more electron-conducting layers, with the electron-conducting layer containing one or more compounds comprising triazine as basic substance.

Electron-conducting layer in organic electroluminescent arrangements

The invention concerns electroluminescent arrangements composed of a substrate, an anode, an electroluminescent element and a cathode, at least one of the two electrodes being transparent in the visible spectrum range. The electroluminescent electrode can contain the following components in sequence: an electroluminescent, hole-injecting, hole-transporting zone, an electron-transporting zone and an electron-injecting zone. The invention is characterized in that the hole-injecting and hole-transporting zone contains an optionally substituted tris-1,3,5-(aminophenyl) benzene compound A or a mixture thereof, and the electroluminescent element optionally contains a further functionalized compound selected from the group comprising hole-transporting materials, a luminescent material B and optionally electron-transporting materials. In addition to component A, the hole-injecting and hole-transporting zone can comprise one a plurality of further hole-transporting compounds. At least one zone is present, individual zones can be omitted and the zone (s) present can assume a plurality of functions.

Electroluminescent arrangements using blend systems

A lightable indicator scale device is created, in particular, for a combination instrument in a motor vehicle, and has a dial which has a first lightable indicator scale in a first area, a second lightable indicator scale in a second area and a third lightable indicator scale in a third area; a first light source device for lighting the first lightable indicator scale and the third lightable indicator scale; a second light source device for lighting the second lightable indicator scale; and a light guide device arranged between the first and second light source devices, on the one hand, and the dial, on the other hand, designed such that it guides light beams of the first light source device to the first area and to the third area; it prevents light beams of the first light source device from reaching the second lightable indicator scale directly; it guides the light beams directed at the third area through the second area, without light scattering into the second lightable indicator scale; and it guide light beams of the second light source device to the second area without light scattering into the first and third lightable indicator scales.

Christoph Jonda

Papers

Synthesis and Application of Dimeric 1,3,5-Triazine Ethers as Hole-Blocking Materials in Electroluminescent Devices

Investigation of the Electronic Properties of Organic Light-Emitting Devices by Impedance Spectroscopy

Electron-conducting layer in organic electroluminescent arrangements

Electroluminescent arrangements using blend systems

Illuminated-display graduated scale device