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OLED color ‘predictable’ by new modeling technique

24 Apr 2013

Manufacture to be "more efficient, lower cost" from greater knowledge of electronic processes.

Until now it has been impossible to predict the exact light color produced by white OLEDs, which consist of stacked, ultra-thin layers, each emitting its own light color, together resulting in white light.

But knowing the exact range of color outputs is now believed to be important considering that many people believe that OLEDs are one of the more significant light sources of the future.

Researchers at Eindhoven University of Technology, Philips Research, Dresden University of Technology and other institutes have developed a method that allows the color of light produced by a specific OLED design to be calculated with high precision. The technique involves modeling the complex processes in OLEDs on a molecular scale.

The researchers say this technique will allow manufacturers to greatly improve their OLED design processes and reduce the cost. At the same time the energy efficiency and lifetime of OLEDs can be increased. The results were first published online on Sunday 14 April 2013 in Nature Materials DOI 10.1038/NMAT3622.

OLED prospects

It appears likely that OLEDs will cause a revolution in the world of lighting. Because they are light-emitting surfaces, they are considered to be visually more attractive than point light sources such as conventional or LED lamps.

They can also be flexible and transparent, which opens up all kinds of new opportunities. Plus – and unlike normal LEDs – OLEDs are typically made of low-cost materials, of which only very thin layers are needed. As a result, the prices of OLEDs are expected to be low once mass production starts.

To predict what kind of light an OLED design will produce, the researchers made computer models of the electronic processes in the OLED at the deepest level. These showed for example the injection of electrical charge, the creation and distribution of the "excitons" – pairs of positively charged electrons and holes in a bound state – and the creation from these of individual photons, the light that is emitted.

Researcher Peter Bobbert of Eindhoven University of Technology commented, “At first we thought it would never be possible. The main difficulty was that each change in the electrical charge also influences all the other charges, which makes the simulation extremely complex. But we succeeded by using Monte Carlo simulations with nanosecond steps. The results proved to correspond very well to measurements carried out at Philips on real OLEDs made at Dresden University of Technology."

One of the results is that the researchers can now predict where light is produced and lost within the ultra-thin layers. This makes it possible to optimize OLEDs so they produce the same amount of light but using much less electric power. The researchers expect that the efficiency can be increased further by a factor of three.

Commercial application

Manufacturers could also use this knowledge and technique to design OLEDs to produce specific colors. They can calculate in advance exactly how thick the different layers need to be, and how much pigment has to be added to the layers.

The shorter and less costly design process will allow the overall development costs to be reduced, leading to lower prices of the final products. Bobbert adds, “This has already been possible for a long time in the field of micro-electronics, with the ability to precisely predict the behavior of integrated circuits. Now we can do the same thing with OLEDs.”

This OLED research was made possible by financial support from the European Union (FP7 project AEVIOM), the Dutch Polymer Institute, NanoNextNL and NanoNed.

The following video shows some recent developments in OLED technology by Philips Lumiblade, presented by the division's communications specialist Dietmar Thomas.

About the Author

Matthew Peach is a contributing editor to optics.org.

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