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  • LEDs and OLEDs

  • What we have here is light emitting diodes, LEDs and what they are is a semiconductor, the diode only conducts electricity in one direction

  • and it stops it going the other way, if you feed it with alternating current it will change it into direct current

  • and if you take a diode and ad various chemical compounds to it, it will emit light

  • This is an LED demo board, typically they make white light with LEDs

  • you have a very efficient blue LED with a yellow phosphor coated device

  • you end up with a nice warm white emission, or

  • you have white emitting LEDs which are a combination of RGB, red green blue emitters inside the LED package.

  • It's another way to make white LEDs

  • Ok, what we are looking at some samples of OLED panels, these are organic light emitting diodes

  • The difference between an LED and an OLED is that with an LED you have to use 3 5 substrates.

  • because of the fact that, when you use something like silicon which is a fourth group element

  • you have an indirect band gap, so that indirect band gap means that the electron and the hole

  • the hole being the absence of an electron, when they come together to form the photon

  • they have to travel in an x-y direction so you are traveling off of

  • a y direction to get to the electron or hole, and as a result you get the release of heat as well as light

  • you get more heat than you do light because of that phenomena, you don't have as much light because

  • you have a lot of other phenomena going on, so that is why they use a lot of 3-5 materials like

  • gallium arsenide to get that light output, and you are limited to those materials to get that effect

  • so when you use OLEDs the difference is you can use any substrate

  • and you use organic materials, which is where the light emission process actually occurs

  • and as a result it allows for a lot more flexibility in terms of the materials and devices you can use.

  • typically we form an indium tin oxide layer, which is a transparent conductive material

  • very commonly used in optoelectronic devices

  • that is sputtered onto the glass substrate, and on top of that ITO film we form a stack of very thin organic material

  • coatings, anywhere from about 5 nanometers thick to about 200 nanometers

  • depending on your device construction, there can be anywhere from 5-10 coatings that we stack on top of each other

  • to make a white device typically we make 3 emission layers, red green and blue, and the combined emission from those layers forms white light

  • through the emission layers there is typically an electron transport layer, and the cathode acts to inject electrons into the device

  • it's also a reflective material which is very important, if its not a reflective metal a lot of the photos will be absorbed at that interface

  • in the off state it is a mirror, what you are seeing is a reflection off of the aluminum cathode

  • the OLED materials are very efficient, and they can efficiently generate photons

  • we can create an OLED device which is 30-40 lumens per watt without using any extraction technology

  • but the potential is there to get well over 100 lumens per watt if we solve some of the problems of light extraction.

LEDs and OLEDs

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B2 US emission electron led device emitting typically

LEDs and OLEDs - How it Works, Inventors

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    bill_1215 posted on 2017/06/30
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