Let's talk about the newest and the hottest kid in the field of display.
That is these OLED-based display, or these organic LED-based display.
And, shown here is a cross-section of this OLED display.
And the first thing you notice looking at
this cross section is that how simple it is.
And how few layers it has. In fact it has only two or three layers.
the first layer you have below is the TFT backplane,
or these backplane made up of these thin film transistors.
And these are typically in the case of OLED display, made of this material
made of this material called poly, low temperature poly silicon.
And these essentially they provide the current
which is needed to drive these OLED displays.
So since it's OLED stands for organic light emitting diode.
And the key.
word over here is a diode. So since it's a diode it needs to be
driven by a current and these thin film transistors provide that current.
As compared to a LCD display where you
just need a voltage to manipulate your display.
And the key layer which is the most important layer for these OLED display is
this OLED layer, which consists of these individual light emitting diode.
So, each of these TFT transistors is driving, This,
OLED layer over here, and they essentially consist
of these R, G, B, light emitting diodes.
And they essentially emit out the light from this light emitting diode.
And since, this layer is at the very top, you directly get
light from the very top of the display, unlike your LCD,
where light is coming from below and it has to pass through a lot of layers.
So you get light from the very top surface which is this light emitting diode layer.
And as a result of that since it has only a few layers and the light is coming
from the very top layer, these OLED-based display have
a very good viewing angle, and so you can
View these displays, you know, at a much
larger angle as compared to LCD based display.
So the key point there is notice how
simple they are and how few layers they have.
So they are very simple things in terms
of the layer structure and how to manufacture them.
So now let's look at the important question of how does this OLED
based display work or you know, how does it exactly emit light?
And that is explained with these figures over here.
And again it's you notice the simplicity in the operation
of this display. So it consists of these different
layers which From the, which make this OLED display.
So to make a light emitting diode, you need a layer which
you can transport your electrons, so you have a electron transport layer.
And then you need a layer which can supply the holes.
So you have this hole transport layer.
And they combine and these electrons and holes combine, and that
generates the light. And to supply these electrons and
holes, you have cathode and that's typically
placed at the bottom of the display.
And then you have anode on the top
and that's made up, again, of transparent material.
So it's made up of this transparent, conducting oxide.
And the most common material for making that
is indium tin oxide or this ITO layer.
And that's it.
So essentially you have
a cathode, you have anode which is transparent.
And you have these different layers, two different layers to transport your
electrons and your holes in terms of band diagrams, so this is how it looks like.
So remember, these are organic LEDs so they are organic
layers and they have these HOMO and LUMO layers which is
equivalent to having conduction band and a valence band in a crystalline material.
And then you have this cathode layer, which is a low volt function layer.
It's made up of materials like Barium, Calcium.
And these these since it's a low work function,
it can easily transport or supply this electrons
into the electron transport layer.
And on the top you have this anode which is made up of ITO.
And the good thing about ITO is it already has a large work function.
So it has this large work function as compared to your cathode, and
it can easily supply these holes to the hole transport layer.
So it supplies these
holes and from here you get your electrons.
And when they meet each other they combine
and they emit light which passes through this anode.
And the light which is reflected back. So you know through this light generation
is in all directions, the light which reaches cathode is again reflected back.
Back by this cathode, and all of that light comes and
passes through your anode.
And the way you generate different colors is again very simple.
So you, how you generate different colors is
that you use different molecules for making these layers.
So shown here are some of these different molecules and they
look like, you know, a lot of organic and benzene rings.
but essentially what they do
is they have different energy different between their HOMO and LUMO layers.
And that gives you different energy of the light coming out.
And that way you're able to generate blue light green light, and red light.
So again, you notice the simplicity in both
the overall structure of the LED, and the simplicity
in making this LED pixel itself. And so this
LED has been organic LED has been around for awhile.
It just, it it it, you know, it
it took a long time for it to reach commercialization.
But the basic phenomena that these organic based molecules
can emit light, as was discovered by Mr. Pope,
in New York University, back all the way back in 1960.
And the first crystal they used to play around with was these anthracene crystal.
And when you apply a large amount of
voltage on these crystals they used to emit light.
And then there was lot of development work which happened in the university
around the 1990s, late 1990s, you know, companies started
to make these displays, and the, you know, the initial
displays were not so big and more recently
in 2010, or you know, around later part of 2000.
there was a lot of interest from, different companies who are trying
to commercialize this technology.
Samsung, in particular, has been a leader in, OLED based display.
As you can see over here, it invested
over, 5 billion dollar of capital into these display.
And most of the Galaxy smartphones, are Galaxy S2, S3.
Or even the Galaxy Note they, they use these OLED.
Based displays that's shown here
is their latest phone. So this is Galaxy S3
and as you can see it it shares its users as Super
AMOLED display so this is more of a marketing term but
what this stands for is active matrix so that's what your AM is.
So it's a active matrix, meaning that each of these
LEDs are connected using a active matrix, so they can be driven individually.
And the key term here is that AMOLED, so it's active matrix based OLED display.
And, these are very prevalent in phones, especially your smart phones.