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.