Encyclopedia of Color Science and Technology

2016 Edition
| Editors: Ming Ronnier Luo

Light-Emitting Diode, OLED

  • Wout van Bommel
Reference work entry
DOI: https://doi.org/10.1007/978-1-4419-8071-7_132

Synonyms

Definition

Light source that produces light as a result of recombination of positively charged holes and negatively charged electrons at the junction of organic, solid-state, p- and n-type planar semiconductor materials.

Solid-State Light Sources

LEDs are solid-state radiators where the light is created inside solid-state material [2, 3, 4]. The light-radiating diode versions are called light-emitting diodes or LEDs. Light-emitting diodes made of organic semiconductor material are referred to as OLEDs; they are planar light sources (Fig. 1). Organic material is a semiconductor chemical compound whose molecules contain carbon and hydrogen (C – H bonds). The name LED is commonly used for light-emitting diodes made of inorganic semiconductor material; they are quasi point light sources. A separate chapter deals with LEDs. Serious development of OLEDs only started in the mid-1990s of the last century. OLEDs can be produced to give most colors of the spectrum and white. The technology permits producing OLED windows that are transparent when not switched on (Fig. 2). Currently, the main application for OLEDs is displays for mobile phones and for other display screens including small television screens. OLED lighting products are now gradually also coming onto the market for illuminating purposes. Initially, the most interesting application for OLEDs, in this respect, is architectural, decorative lighting. For general lighting purposes the efficacies have to be improved much further.
Light-Emitting Diode, OLED, Fig. 1

Flat OLED light sources

Light-Emitting Diode, OLED, Fig. 2

OLED window [1]

Working Principle

The process that is responsible for the emission of light in OLEDs is very similar to that with LEDs: positively charged holes and negatively charged electrons are pushed through semiconductor layers towards each other and recombine (see entry “ Light-Emitting Diode, LED”). Part of these recombinations results in the emission of light. The color of the light is dependent on the composition of the semiconductor material. White light can be obtained by bringing phosphorescent material in the emissive layers.

Materials and Construction

The semiconductor organic layers are placed between electrodes, the one on the light-escape side being transparent (Fig. 3). The layers are supported by a glass substrate and, for protection of the organic materials against oxygen and water, are sealed in glass. Development is going on to substitute the glass seal by thin-film encapsulation. This development not only reduces the thickness and weight of OLEDs but also opens up the possibility of bendable OLEDs. The first laboratory examples have already been produced.
Light-Emitting Diode, OLED, Fig. 3

Composition of an OLED [1]

Properties

Commercial OLED products for lighting are just recently coming onto the market. Data of the properties of commercial products are only scarcely available. It is expected that they will change relatively fast the coming years. Only a rough indication will therefore be given here.

System Luminous Efficacy and Brightness

Commercially available white OLEDs now have efficacies between 15 and 30 lm/W. Ultimately, white-light, large-sized OLEDs with efficacies up to 150 lm/W would seem to be possible. Products with luminance values of up to 2,000 cd/m2 have been shown. Compare this with a luminance value of some 6,000–10,000 cd/m2 of fluorescent tubes.

Dimensions

Today sizes go up to some 30 × 30 cm. The expectation is that that sizes of more than 100 × 100 cm will be available in just a few years.

Lifetime

Lifetimes of some 10,000 h have been reported.

Color Properties

As has been mentioned, by choosing different materials of semiconductor material, different colors are obtained. The quality of white light depends upon the combination of the semiconductor and phosphorescent material used. Spectra similar to those of inorganic LEDs are obtained (see entry “ Light-Emitting Diode, LEDD”).

Cross-References

References

  1. 1.
    Van Bommel, W.J.M., Rouhana, A.: Lighting Hardware: Lamps, Gear, Luminaires, Controls. Course book, Philips Lighting, Eindhoven (2012)Google Scholar
  2. 2.
    Schubert, E.F.: Light Emitting Diodes, 2nd edn. Cambridge University Press, Cambridge (2006)CrossRefGoogle Scholar
  3. 3.
    Mottier, P.: Led for Lighting Applications. Wiley, Hoboken, NJ (2010)Google Scholar
  4. 4.
    DiLaura, D.L., Houser, K., Mistrick, R., Steffy, G.: Illuminating Engineering Society of North America, New York. 10th edn. (2011)Google Scholar

Copyright information

© Springer Science+Business Media New York 2016

Authors and Affiliations

  1. 1.NuenenThe Netherlands