All About OLED Display

Today we are going to talk about OLED Display. Hope you like it!

Introduction About OLED Display

OLED (Organic Light Emitting Diodes) is a flat light emitting technology, made by placing a series of organic thin films between two conductors. When electrical current is applied, a bright light is emitted. OLEDs can be used to make displays and lighting, because OLEDs emit light they do not require a backlight and so are thinner and more efficient than LCD displays (which do require a white backlight). And OLEDs are used to create digital displays in devices such as television screens, computer monitors, portable systems such as mobile phones, handheld game consoles and PDAs.

Before moving to our classroom i would like to introduce about AMOLED and OLED

1) AMOLED Display:

AMOLED stands for Active Matrix Organic Light Emitting Diode. A step ahead of OLED screens, the AMOLED screens can control each pixel individuality while maintaining the properties of an OLED panel. AMOLED screens use a different subpixel arrangement which can reduce the image quality a bit.

2) OLED Display:

An Organic Light Emitting Diode (OLED) display technology is much better as compared to the LCD display technology because of its excellent colour reproduction, faster response times, wider viewing angles, higher brightness and extremely light weight designs. OLEDs are solid-state devices composed of thin films of organic molecules that create light with the application of electricity.

History of OLED

OLED diode technology was invented by "researches a Eastman Kodak" company in 1987. Chemists,Ching W Tang and Steven Van Slyke were the principle inventors. In June of 2001, they received an Industrial Innovation Award from the American Chemical Society for their work with organic light emitting diodes.

Kodak has released several of the earliest OLED equipped products including first digital camera with an 2.2" OLED display with 512 x 218 pixels, the 2003 EasyShare LS633. Kodak has since licensed their OLED technology to many companies and they are still researching OLED light technology display technology and other projects.

• In early 2000s researchers at Pacific Northwest National Laboratory and the Department of Energy, invented two technologies necessary to make flexible OLEDs:
• First  Flexible Glass an engineered substrate that provides a flexible surface and second a Barix thin film coating that protects a flexible display from harmful air and moisture.

How OLED Works

OLED components include organic layers that are made of organic molecules or polymers.

An OLED is a solid-state semiconductor device that is 100 to 500 nanometers thick or about 200 times smaller than a human hair. OLEDs can have either two layers or three layers of organic material; in the latter design, the third layer helps transport electrons from the cathode to the emissive layer. We'll be focusing on the two-layer design.

An OLED consists of the following parts:-

• Substrate: (clear plastic, glass, foil) - The substrate supports the OLED.
• Anode: (transparent) - anode contains "Holes" that absorb the electrons when current flows through the device.
• Organic layers: These layers are made of organic materials or polymers.
• Conducting layer: This layer is made of organic plastic materials that transport "holes" from the anode. One conducting polymer used in OLEDs is polyaniline.
• Emissive layer: This layer is made of organic plastic materials (different ones from the conducting layer) that transport electrons from the cathode; this is where light is made. One polymer used in the emissive layer is polyfluorene.
• Cathode: (may or may not be transparent depending on the type of OLED) - The cathode injects electrons when a current flows through the device.

The biggest part of manufacturing OLEDs is applying the organic layers to the substrate. This can be done in three ways:

• Vacuum deposition or vacuum thermal evaporation (VTE) - In a vacuum chamber, the organic molecules are gently heated (evaporated) and allowed to condense as thin films onto cooled substrates. This process is expensive and inefficient.
• Organic vapor phase deposition (OVPD) - In a low-pressure, hot-walled reactor chamber, a carrier gas transports evaporated organic molecules onto cooled substrates, where they condense into thin films. Using a carrier gas increases the efficiency and reduces the cost of making OLEDs.
• Inkjet printing - With inkjet technology, OLEDs are sprayed onto substrates just like inks are sprayed onto paper during printing. Inkjet technology greatly reduces the cost of OLED manufacturing and allows OLEDs to be printed onto very large films for large displays like 80-inch TV screens or electronic billboards.

How Does OLED Emit Light?

OLED light is created through a process called electrophosphorescence.

OLEDs emit light in a similar manner to LEDs, through a process called Eletrophosphorescence.

The process is as follows:

• The battery or power supply of the gadget containing the OLED applies a voltage over the OLED.
• An electrical current streams from the cathode to the anode through the natural layers (an electrical current is a stream of electrons). The cathode offers electrons to the emissive layer of natural atoms. The anode expels electrons from the conductive layer of natural particles.
• At the limit between the emissive and the conductive layers, electrons discover electron openings. At the point when an electron finds an electron opening, the electron fills the gap (it falls into a vitality level of the particle that is feeling the loss of an electron). At the point when this happens, the electron surrenders vitality as a photon of light
• 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.

Small Molecule OLED vs. Polymer OLED
The sorts of particles utilized by Kodak researchers as a part of 1987 in the principal OLEDs were little natural atoms. Albeit little particles transmitted splendid light, researchers needed to store them onto the substrates in a vacuum (a costly assembling process called vacuum affidavit.
Since 1990, specialists have been utilizing huge polymer particles to emanate light. Polymers can be made less extravagantly and in expansive sheets, so they are more reasonable for extensive screen shows.

Types of OLED

There are several types of OLEDs:

a) Passive-matrix OLED (PMOLED)

b) Active-Matrix OLED (AMOLED)

c) Transparent OLED

d) Top-emitting OLED

Above 4 types are the common types of LED, and there are more LED type such as Foldable OLED and White LED.

Differences and Benefits

Efficient:

• OLEDs require far less voltage than different types of lighting. In addition, they are cool to the touch paying little respect to what extent they've been on. Keep in mind the absence of the backdrop illumination we specified before? Not just does that make OLEDs brighter, it additionally makes them expend less power – expanding battery life by up to 40% when contrasted with other lighting sources.

Eco-friendly:

• The natural part of OLEDs is a genuine differentiator. OLEDs are created without the utilization of any dangerous materials, similar to Mercury for example, significantly decreasing their ecological effect. In a few examples, OLEDs can work without UV emanations also. Basically, they are the most eco-accommodating structure if lighting on the planet.

Ultra-thin, Transparent:

• OLEDs can be delivered in a manner that they can twist without breaking – making them to a great degree sturdy (this is even valid for those that aren't intended to be adaptable). Since the OLED boards are so thin, they odds of them "breaking" for ordinary use is practically non-existent. Alternate clear contrast amongst OLEDs and different types of lighting is their straightforwardness – the natural film can pass light in both directions.

OLED Advantages:

• OLED can be flexible instead of rigid.
• OLED substrates can be plastic rather than the glass used for LEDs and LCDs.
• OLEDs are brighter than LEDs.
• They consume much less power and hence result in low battery consumption.
• OLEDs have large fields of view, about 170 degrees.

OLED Disadvantages:

• Lifetime is not as long as compared to AMOLED Panels.
• Manufacturing processes are expensive right now.
• Water can easily damage OLEDs.

source: http://en.miui.com/forum.phpmod=viewthread&tid=574549&highlight=all%2Babout%2Bdisplay