OLED SCREEN TECH

Imagine watching HD movies on a huge TV that is less than a quarter-inch thick and hardly weighs 1-2 kg, consumes very less power compared to the LCD TVs we get today and can be rolled up when you’re not using it. What if you could have a display monitor built into your clothing? What if the wind shield of your car could have the maps and GPS data embedded on to it when you drive? These devices may be possible in the near future with the help of a technology called organic light-emitting diodes (OLEDs).

Source: mobileinc.co.uk

Source: http://www.oled-info.com

OLEDs are solid-state devices composed of thin films of organic molecules that create light with the application of electricity. OLEDs can provide brighter, crisper displays on electronic devices and use less power than conventional LEDs or LCDs used today.

OLED COMPOSITION AND WORKING

Source: howstuffworks.com

OLED is compose of the following components:

• Cathode (it injects electrons when a current flows through the device)                               
• Emissive Layer(organic layer transporting electrons from cathode)
• Conducting layer(organic layer that transports holes from the anode)
• Anode(adds holes to the conductive layer)
• Substrate(supporting layer)

When a voltage is applied across the OLED, an electrical current flows from the cathode to the anode through the organic layers. The cathode gives electrons to the emissive layer of organic molecules. The anode removes electrons from the conductive layer of organic molecules(it adds electron holes). At the boundary between the emissive and the conductive layers, when an electron finds an electron hole, the electron fills the hole and gives up energy in the form of a photon of 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.

There are several types of OLEDs:

• Passive-matrix OLED
• Active-matrix OLED
• Transparent OLED
• Top-emitting OLED
• Foldable OLED
• White OLED

Let us discuss about the most important types: passive-matrix and active-matrix OLEDs.

Passive-matrix OLED (PMOLED)

PMOLEDs have strips of cathode, organic layers and strips of anode. The anode strips are arranged perpendicular to the cathode strips. The intersections of the cathode and anode make up the pixels where light is emitted. External circuitry applies current to selected strips of anode and cathode, determining which pixels get turned on and which pixels remain off. Again, the brightness of each pixel is proportional to the amount of applied current.

                               Source: howstuffworks.com

PMOLEDs are easy to make, but they consume more power than other types of OLED, mainly due to the power needed for the external circuitry. PMOLEDs are most efficient for text and icons and are best suited for small screens (2- to 3-inch diagonal) such as those you find in cell phones, PDAs and MP3 players. Even with the external circuitry, passive-matrix OLEDs consume less battery power than the LCDs that currently power these devices.

Active-matrix OLED (AMOLED)
AMOLEDs have full layers of cathode, organic molecules and anode, but the anode layer overlays a thin film transistor (TFT) array that forms a matrix. The TFT array itself is the circuitry that determines which pixels get turned on to form an image.

Source: howstuffworks.com

AMOLEDs consume less power than PMOLEDs because the TFT array requires less power than external circuitry, so they are efficient for large displays. AMOLEDs also have faster refresh rates suitable for video. The best uses for AMOLEDs are computer monitors, large-screen TVs and electronic signs or billboards. Currently we can see a lot of smartphones in the market which make use of the AMOLED screen (prominent ones include Samsung Galaxy wave II, Nokia lumia 800)

Transparent OLEDs have only transparent components and are up to 85 percent as transparent as their substrate when turned off. When a transparent OLED display is turned on, it allows light to pass in both directions. They have great applications in augmented reality based applications where we have to embed the semantic data on to a screen.

Foldable OLEDs have substrates made of very flexible metallic foils or plastics. Foldable OLEDs are very lightweight and durable which makes them an ideal choice for use in smart phone which have to be handled delicately.

White OLEDs emit white light that is brighter, more uniform and more energy efficient than that emitted by fluorescent lights. Since OLEDs can be made in large sheets, they can replace fluorescent lights that are currently used in homes and buildings. Their use could potentially reduce energy costs for lighting.

OLED vs LCD

OLED displays have the following advantages over LCD displays:

• Lower power consumption
• Faster refresh rate and better contrast
• Greater brightness – The screens are brighter, and have a fuller viewing angle
• Exciting displays – new types of displays, that we do not have today, like ultra-thin, flexible or transparent displays
• Better durability – OLEDs are very durable and can operate in a broader temperature range
• Lighter weight – the screen can be made very thin, and can even be ‘printed’ on flexible surfaces

Disadvantages of the OLED

OLEDs aren’t perfect. First of all, today it costs more to produce an OLED than it does to produce an LCD, although this should hopefully change in the future, as OLEDs has a potential to be even cheaper than LCDs because of their simple design.

OLEDs have limited lifetime which was quite a problem a few years ago, but there has been constant progress, and today this is almost a non-issue.

Futuristic Applications

In the future, we will be able to see flexible and transparent OLED panels. This will open up a whole world of exciting applications, such as:

• Curved OLED displays, placed on non-flat surfaces
• Rollable OLED TV screens
• Wearable OLEDs
• Transparent OLEDs embedded in windows
• OLEDs in car windshields
• OLED lamps
• OLED military suits used for camouflaging

And many more gadgets that we see in the sci-fi Hollywood flicks that we watch today………