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Introduction to OLED technology

 OSRAM
  17th-Jul-2015
Description: General characteristics- Structure: An organic light-emitting diode (OLED) consists of several semiconducting organic layers sandwiched between two electrodes, at least one of them being transparent. Two simplified de vice structures are shown in figure 1: a one-side emitting device (left) and a transparent one which emits light both upwards and downwards (right). The device is fabricated by sequentially depositing organic layers on a conducting substrate followed by another conducting electrode. A common device structure comprises a glass substrate coated with indium tin oxide (ITO) as transparent anode and a thin, opaque metal fi lm as cathode. The organic stack including the electrodes is usually thinner than 1 μm. Two classes of organic materials are commonly used for organic light-emitting devices: polymeric substances and so-called “small molecule materials” which do not exhibit any orientating property and therefore form amorphous films. One interesting aspect of organics-based optoelectronics is the possibility to use simple screen printing or wet deposition techniques for cost-effective fabrication of large-area devices. Nowadays, this applies only to polymeric organics, whereas evaporating techniques still have to be applied for small molecules. Hopping transport and recombination When a DC bias is applied to the electrodes, the injected electrons and holes can recombine in the organic layers and emit light of a certain color depending on the properties of the organic material. Since charge carrier transport in organic semiconductors relies on individual hopping processes between more or less isolated molecules or along polymer chains (figure 2), the conductivity of organic semiconductors is several orders of magnitude lower than that of their inorganic counterparts. Furthermore, the concept of energetic bands with highly delocalized wave functions is not applicable to organic electronics. Instead of “valence band” and “conduction band”, the relevant terms are “HOMO level” (highest occupied molecular orbital level) and “LUMO level” (lowest unoccupied molecular orbital level).
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Domain: Energy
Category: Lighting
Contributing Organization: OSRAM GmbH
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Contents:
www.osram-oled.com

Introduction to OLED technology
1. General characteristics
1.1. Structure
An organic light-emitting diode (OLED) consists of several semiconducting organic layers sandwiched
between two electrodes, at least one of them being transparent. Two simplified de vice structures are shown
in figure 1: a one-side emitting device (left) and a transparent one which emits light both upward ... See more

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