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Displays with a future: The world's largest OLED display — manufactured by Mitsubishi Electric — is currently at EMD in DarmstadtStage Image

Displays with a future: The world's largest OLED display — manufactured by Mitsubishi Electric — is currently at EMD in Darmstadt

© Mitsubishi

Displays made of organic light-emitting diodes

For a spectacular TV viewing experience

2013/4/16

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Although displays made of organic light-emitting diodes (OLEDs) offer many advantages, they are difficult to produce using conventional methods. That’s why the printer manufacturer Seiko Epson is working together with EMD to develop technologies for printing OLED displays. Initial results show that the technique works in practice.

Displays made of organic light-emitting diodes (OLEDs) improve the television viewing experience by offering brilliant colors and extremely sharp contrasts irrespective of the viewing angle. And unlike conventional liquid crystal displays (LCDs), the self-luminous OLEDs do not need any backlighting. As a result, they consume less electricity.

Pinpoint precision in production


The individual pixels, each of which consists of one red, one green, and one blue light-emitting diode, have a filigree structure that poses a considerable challenge for the production of OLED displays.

“The first large-format printed OLED displays should be commercially available within a few years.“

Thomas Kessler
responsible for the market penetration of OLED technologies
at EMD

Even though up to ten different materials have to be applied to a glass plate for every diode, all of the layers combined are thinner than a human hair. Together with the glass plate, the material layers are currently less than one millimeter thick. 

The materials also have to be applied on the surface in tiny amounts and with pinpoint accuracy. The closer the diodes are to one another, the greater the display’s resolution. While researching OLED displays, EMD initially focused on lithographic vacuum processes, in which a glass plate is laid into a vacuum chamber, where it is covered with a metal stencil.  


The vaporized OLED materials are deposited in the cut-outs of the stencil when they cool off. The materials consist of molecules that have electrically insulating, semiconducting or conducting properties as a result of their chemical composition. The evaporation and deposition process is continued with a variety of molecules and stencils until the light-emitting diodes have filled up the stencil cutouts.

  • Structure of an OLED: 1: Light beam; 2: Glass substrate; 3: Transparent anode; 4: Charge carrier transport layer; 5: Light-emitting layer; 6: Charge carrier transport layer; 7: Metal cathodeEnlarge
  • Structure of an OLED: 1: Light beam; 2: Glass substrate; 3: Transparent anode; 4: Charge carrier transport layer; 5: Light-emitting layer; 6: Charge carrier transport layer; 7: Metal cathode
    © EMD

    2013/4/16

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    Today this technique is primarily used commercially to manufacture small OLED displays, such as those in cell phones. However, the technique also has three major drawbacks. First, all of the OLED material that is deposited directly onto the stencil or within the vacuum chamber is lost. Second, the metal stencil changes its shape when it heats up or cools, thus making it more difficult to apply the layers precisely onto the glass plate.

    Finally, the layers are applied at high temperatures and in a toxic atmosphere, which increases the costs for energy as well as for environmental protection and occupational safety measures.

     
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