LED displays are The most common types of displays around. They’re everywhere, from your television to your devices to the jumbotrons at times square.
An LED is an acronym for a Light Emitting Diode. What we know as LED screens are not actually LED screens. Proper LED screens should have light-emitting diodes at each pixel. Emitting light from there and no longer needing a backlight as in LCDs.
The LED screens we have today are actually LCDs screens but instead of using a CCFL (Cold-Cathode Fluorescent lamp) as a backlight source, as LCDs do, they use light-emitting diodes as a backlight source.
They work in the same way as LCDs; using polaroids and light filters and liquid crystals. Because LED screens use LEDs as their backlight source, they are more power-efficient and cost less to manufactures.
OLED. OLED Are organic LEDs. They are organic because they use organic polymers. OLEDs typically have 2 or 3 organic layers. A typical OLED consist of the following parts
Substrate; this is either clear plastic, glass, or foil. The substrate supports the OLED.
Anode; the anode removes electrons, creates electron holes when current flows through the device.
Organic layers; these are typically layers made of organic molecules or polymers
Conducting layers; they are made of organic molecules that move the electron holes from the anode
Emissive layer; This layer is made up of different organic molecules that transport electrons from the cathode (where the light is made)
Cathode; The cathode creates light by releasing electrons current flows through it. The cathode may or may not be transparent.
How OLEDs Work
OLEDs are work significantly different from LCDs or LEDs. OLEDs have Light-emitting diodes in each pixel which can be controlled individually.
- Electricity is supplied and a voltage across the OLED is applied
- An electrical current flows from the cathode to the anode through the organic layers (an electrical current is a flow of electrons). The cathode gives electrons to the emissive layer of organic molecules. The anode removes electrons from the conductive layer of organic molecules. (This is the equivalent to giving electron holes to the conductive layer.)
- At the boundary between the emissive and the conductive layers, electrons find electron holes. When an electron finds an electron-hole, the electron fills the hole (it falls into an energy level of the atom that’s missing an electron). When this happens, the electron gives up energy in the form of a photon of light (see How Light Works).
- The OLED emits light.
- The color of the light depends on the type of organic molecule in the emissive layer. Manufacturers place several types of organic films on the same OLED to make color displays.
- The intensity or brightness of the light depends on the amount of electrical current applied: the more current, the brighter the light.
TYPES OF OLEDs
Passive Matrix OLED PMOLED
With passive matrix OLED, the cathode is arranged into strips and the anodes are also arrange into striped. Placed perpendicularly to the cathode strips. The intersection of these strips forms a pixel. Current is applied to selected strips of cathode and anode and the amount of electricity determines how bright the pixel will be.
PMOLEDs are relatively easy to make but they are more power-consuming.
Active Matrix OLED AMOLED
Here, the cathode and anodes are full layers. A thin film transistor array, that forms a matrix exists between the cathode and anode. The TFT is what determines which pixels get turned on or off,
They are less power-hungry, have faster refresh rates, and most commonly found in smartphone displays.
Here, all the components are transparent. When everything is turned off, all the components are about 85 percent as transparent as the substrate.
Top emitting OLED
These OLEDs have a substrate that is either opaque or reflective. These substrates are mostly used in AMOLED displays.
Here, the substrate is made of flexible metallic foils or plastic. Its the substrate that gives the display is flexibility or rigidity. These types are very lightweight and do not easily break because the OLED is not as brittle.
This display type can be used to create foldable displays or sewed onto cloth to make smart cloth.
These emit a white light that is brighter and more uniform, can be produced in large sheets and used as light bulls. They are also more efficient than standard fluorescent lights.
Advantages of OLEDs
OLEDs have several advantages over LCDs.
They are thinner, lighter, and more flexible than crystalline layers in LEDs of LCD.
OLEDs can be brighter.
OLEDs do not need a backlight like LEDs or LCDs. So they are more energy-efficient.
OLEDs have wider field of views than LCDs, of about 170 degrees.
Some drawbacks of OLEDs are
red and green OLED subpixels typically have a lifetime of about 46,000 to 230,000 hours. Blue subpixels, however have significantly shorter lifetimes of about 14,000 hours.
Making OLEDS is typically more expensive than other display types.
OLEDs typically suffer from issues that LCDs do not. Like Screen Burn-in
Water can easily damage OLEDs