Light-Emitting Diode, OLED
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
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
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.
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.
Lifetimes of some 10,000 h have been reported.
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”).
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