Organic electronics are beginning to make significant inroads into the commercial world, and if the field continues to progress at its current, rapid pace, electronics based on organic thin-film materials will soon become a mainstay of our technological existence. Already products based on active thin-film organic devices are in the market place, most notably the displays of several mobile electronic appliances. Yet the future holds even greater promise for this technology, with an entirely new generation of ultralow-cost, lightweight and even flexible electronic devices in the offing, which will perform functions traditionally accomplished using much more expensive components based on conventional semiconductor materials such as silicon.

The path to ubiquitous and low-cost organic electronic appliances on plastic

White organic light-emitting devices (WOLEDs) have advanced over the last twelve years to the extent that these devices are now being considered as efficient solid-state lighting sources. Initially, WOLEDs were targeted towards display applications for use primarily as liquid-crystal display backlights. Now, their power efficiencies have surpassed those of incandescent sources due to improvements in device architectures, synthesis of novel materials, and the incorporation of electrophosphorescent emitters. This review discusses the advantages and disadvantages of several WOLED architectures in terms of efficiency and color quality. Hindrances to their widespread acceptance as solid-state lighting sources are also noted.

White Organic Light‐Emitting Devices for Solid‐State Lighting

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

Most present-day semiconductor devices use inorganic crystalline materials, with single-crystalline silicon dominating other materials like GaAs by about a factor of 1000. Despite the advantages of single-crystalline inorganic semiconductors like high room-temperature mobility (up to 1000 cm2/(V s)) and high stability, these materials are less suitable for low-cost and large-area applications. Additionally, silicon is an indirect semiconductor and therefore is not well suited for optoelectronic applications like light-emitting diodes. Solar cells from silicon are expensive and require a large amount of energy for their fabrication, leading to a long energy payback time. As an alternative, organic semiconductors have recently gained much attention (for review articles, see refs 1 -3 (OLEDs), ref 4 (organic electronics in general), and refs 5 and 6 (organic solar cells)). Originally, much of the research concentrated on single crystals, which can have mobilities of a few cm2/(V s) at room temperature and even much higher values at low temperature, as shown in the pioneering work of Karl et al.7 However, for practical applications, thinfilm organic semiconductors with disordered morphology, such as evaporated small-molecule compounds or polymers processed from solution, are prevailing. Organic semiconductors are already broadly applied as photoconductors for copiers and laser printers. * Corresponding author. E-mail: leo@iapp.de. Web address: www.iapp.de. 1233 Chem. Rev. 2007, 107, 1233−1271

Highly efficient organic devices based on electrically doped transport layers.

The present invention provides a heterocyclic compound and an organic light-emitting device including the heterocyclic compound. The organic light-emitting devices using the heterocyclic compounds have high-efficiency, low driving voltage, high luminance and long lifespan.

Organic light-emitting device

Bright organic electroluminescent devices were developed using a metal-doped organic layer as an electron-injecting layer at the interface between the cathode and the emitter layer. The typical device structure is a glass substrate/indium-tin oxide/arylamine/tris(8-quinolinolato)Al (Alq)/metal-doped Alq/Al. Dopant metals are highly reactive metals such as Li, Sr, and Sm. A device with Li-doped Alq layer showed high luminance of over 30 000 cd/m2, while a device without the metal-doped Alq layer exhibited only 3400 cd/m2. These results suggest that the Li doping to the Alq layer generates the radical anions of Alq serving as intrinsic electron carriers, which result in low barrier height for electron injection and high electron conductivity of the Li-doped Alq layer.

Bright organic electroluminescent devices having a metal-doped electron-injecting layer

Novel structure of Multiphoton Emission (MPE) organic EL (OEL) device capable of exceeding 100% quantum efficiency was fabricated. The principle of the device is that a plurality of conventional OEL structure (emissive unit) are stacked and divided by Charge Generation Layer (CGL) that works as an injector of electron-hole pair upon voltage application. Tripled stacked MPE successfully achieved 48 cd/A for the emission from fluorescent green dye coumarin C545T.

27.5L: Late-News Paper: Multiphoton Organic EL device having Charge Generation Layer

Organic electroluminescent (EL) devices with a novel hole-injecting layer using Lewis-acid-doped arylamine derivatives were investigated. The hole-injecting layer was fabricated by coevaporation of a Lewis acid, FeCl3, and an arylamine derivative, N,N'-dinaphtyl-N,N-diphenyl bendizine (α-NPD). Optical absorption spectra of the Lewis acid-doped layer indicated that charge transfer (CT) complexes between α-NPD and FeCl3 were formed. Organic EL devices having a structure of ITO/FeCl3-doped α-NPD (1000 A)/α-NPD (500 A)/tris(8-quinolinolato)aluminum (III) (Alq3) (700 A)/LiF (5 A)/Al exhibited low drive voltages and high luminance of 27000 cd/m2 at 10 V.

https://iopscience.iop.org/article/10.1143/JJAP.41.L358/pdf

Organic Electroluminescent Devices with a Vacuum-Deposited Lewis-Acid-Doped Hole-Injecting Layer

We have developed organic EL (OEL) devices, in which extremely high quantum efficiency of over 100% can be obtained. In order to generate more than one photons per injected electron, “Charge Generation Layers (CGLs)” are placed between emissive units. At CGLs, electrons and holes are generated upon voltage application, and injected to the adjacent organic emissive layers. By using one CGL and two emissive units, quantum efficiency can be doubled compared to the conventional OEL device, and using two CGLs and three emissive units, quantum efficiency can be tripled. One of the OEL device using two CGLs and three emissive units, an extremely high efficiency of 48 cd/A (ca. 14% external) was obtained, which exceeds the so-called theoretical upper limit of 5%. Examples of such “multiphoton emission” (MPE) devices will be introduced.

27.1: Invited Paper: High Efficiency Organic EL Devices having Charge Generation Layers

We developed novel cathode systems, composed of metal complexes, for organic electroluminescent (EL) devices. Alkaline metal complexes, such as mono(8-quinolinolato) lithium (Liq), were used as a cathode interface layer in combination with metallic Al as a cathode material. Similarly, doping the organic electron-transporting layer with alkaline metal complexes was also effective in facilitating the electron injection from the cathode to the organic layer, which results in reducing the drive voltage. In both cases, we assume that alkaline metal ions in the complexes are reduced to free metal by thermally activated Al. Then, the free alkaline metal reacts with electron-transporting materials, forming the radical anions, which facilitate electron injection from the Al cathode.

https://iopscience.iop.org/article/10.1143/JJAP.41.L800/pdf

Toshio Matsumoto

Papers

Bright organic electroluminescent devices having a metal-doped electron-injecting layer

27.5L: Late-News Paper: Multiphoton Organic EL device having Charge Generation Layer

Organic Electroluminescent Devices with a Vacuum-Deposited Lewis-Acid-Doped Hole-Injecting Layer

27.1: Invited Paper: High Efficiency Organic EL Devices having Charge Generation Layers

Organic Electroluminescent Devices Having Metal Complexes as Cathode Interface Layer