Working Of OLED and its Advantages Over LED & LCD

What is OLED ?

Here in “OLED”, ‘O’ stands for “organic” & ‘LED’ stands for “Light Emitting Diode”. Organic substances include carbon containing compounds like sugar, wood, etc. Organic Light Emitting Diode (OLEDs) are solid-state devices similar to LED which emits light on the application of electricity. This devices are composed of organic molecules that create light when applied electricity on it. It is proved OLEDs produces brighter & crisper display than regular CRT or LED displays. Moreover these OLEDs consume less power than LED or LCD which are used today.

 What is new in OLED ?

Lightning fast response with a ‘wide angle’ view offering exceptional color reproduction, outstanding Contrast levels, and high Brightness. Also the key merit of the application is that the devices are of minute width and light weight. OLED is the holy grail of TV Display technologies! Organic light emitting diodes have been receiving a lot of attention over the world as a new type of display technology. OLEDs have many advantages over conventional display technologies. First, the fabrication process is easy, and devices are thinner and lighter than those fabricated by cathode ray tube (CRT) display technology.
Second, there are also some advantages over liquid crystal (LCD) displays: OLEDS can be viewed from different angles and don’t need a backlight. Finally, the drive voltage and power consumption are low. The first commercial OLED display was introduced by Pioneer Electronics as the front panel of a car stereo in 1997.

Primary look at working of OLED:

A Layer of organic material is sandwiched between two conductors (an anode and a cathode), which in turn are sandwiched between a glass top plate (seal) and a glass bottom plate (substrate). When electric Current is applied to the two conductors, a bright, electro-luminescent light is produced directly from the organic material.

Components which constitute OLED:

1.        Substrate (clear plastic, glass, foil) - The substrate supports the OLED.

2.       Anode (transparent) - The anode removes electrons (adds electron "holes") when a current flows through the device.

3.       Organic layers - These layers are made of organic molecules or polymers.

a.     Conducting layer - This layer is made of organic plastic molecules that transport "holes" from the anode. One conducting polymer used in OLEDs is polyaniline.

b.     Emissive layer - This layer is made of organic plastic molecules (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.

4.       Cathode – Depending on the type of OLED, cathode may or may not be transparent. The cathode injects electrons when a current flows through the device.

Construction of OLED:

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

1.     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.

2.     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.

3.     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.

………………………………………………………………………………………

OLED-Manufacturing Process:

How will OLEDs Emit Light?

The process is little similar to that of LED. Here the process is named as electrophosphorescence. Its schematic diagram is as follows:

The process is as follows:

1.     The battery or power supply of the device containing the OLED applies a voltage across the OLED.

2.     An electrical current flows from the cathode to the anode through the organic layers (an electrical current is a flow of electrons).

3.     The cathode gives electrons to the emissive layer of organic molecules.

4.     The anode removes electrons from the conductive layer of organic molecules. (This is the equivalent to giving electron holes to the conductive laye).

5.     At the boundary between the emissive and the conductive layers, electrons find electron holes.

6.     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).

7.     The OLED emits light.

8.     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.

9.     The intensity or brightness of the light depends on the amount of electrical current applied: the more current, the brighter the light.

How is color created?

OLED has more control over color expression because it only expresses pure colors when an electric Current stimulates the relevant Pixels. The OLED primary color matrix is arranged in red, green, and blue Pixels, which are mounted directly to a printed circuit board. Each individual OLED element is housed in a special "micro-cavity" structure designed to greatly reduce ambient light interference that also works to improve overall color Contrast.

The thickness of the organic Layer is adjusted to produce the strongest light for each of the colors “red, green and blue - used to render the color picture. The three colors are further refined by a color filter, which purifies each color without the need for a polarizer, rendering outstanding color purity.

Advantages of OLED over contemporary Technology

The LCD is currently the display of choice in small devices and is also popular in large-screen TVs. Regular LEDs often form the digits on digital clocks and other electronic devices. OLEDs offer many advantages over both LCDs and LEDs:

The plastic, organic layers of an OLED are thinner, lighter and more flexible than the crystalline layers in an LED or LCD.

Because the light-emitting layers of an OLED are lighter, the substrate of an 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. Because the organic layers of an OLED are much thinner than the corresponding inorganic crystal layers of an LED, the conductive and emissive layers of an OLED can be multi-layered. Also, LEDs and LCDs require glass for support, and glass absorbs some light. OLEDs do not require glass.

OLEDs do not require backlighting like LCDs. LCDs work by selectively blocking areas of the backlight to make the images that you see, while OLEDs generate light themselves. Because OLEDs do not require backlighting, they consume much less power than LCDs (most of the LCD power goes to the backlighting). This is especially important for battery-operated devices such as cell phones.

OLEDs are easier to produce and can be made to larger sizes. Because OLEDs are essentially plastics, they can be made into large, thin sheets. It is much more difficult to grow and lay down so many liquid crystals.

OLEDs have large fields of view, about 170 degrees. Because LCDs work by blocking light, they have an inherent viewing obstacle from certain angles. OLEDs produce their own light, so they have a much wider viewing range.

Problems with OLED
OLED seems to be the perfect technology for all types of displays, but it also has some problems:

Lifetime - While red and green OLED films have longer lifetimes (46,000 to 230,000 hours), blue organics currently have much shorter lifetimes (up to around 14,000 hours) Manufacturing - Manufacturing processes are expensive right now.

Water - Water can easily damage OLEDs.

Particulars & Specifications of OLED devices

To enhance the colour or brightness, manufacturers can add complex chains of molecules (polymers) to the carbon-based layers.

Unlike LCDs, which require backlighting, OLED displays are "emissive" devices, meaning they emit light rather than modulate transmitted or reflected light.

Thin organic layers serve these displays as a source of light, which offers significant advantages in relation to conventional technologies:

Ø     brighter and more brilliant picture

Ø     unlimited viewing angle

Ø     low power consumption

Ø     economic production

Ø     fast "response time"

The fundamentals for a step forward of this technology in the market, which is estimated in 2010 to be worth over USD 2 billion, are the optimization of certain critical performance data such as lifetime and efficiency. This requires innovations in materials meaning that chemistry will decide about the future and the success of the OLED technology. OLEDs - Organic Light-Emitting Diodes are the light of the future

Video wallpaper - just a millimeter thick - could transform your living room wall into a flat screen and electronic film as thin as a sheet of paper could serve as your screen for the internet, the news, images or games. In future, all of this will be possible thanks to organic light-emitting diodes, so-called OLEDs. In this episode you will learn more about this revolution in lighting technology:
OLED Podcast from BASF! Learn all about OLED Technology! 

Why are the OLED-Display technologies even better than the LCD or plasma technology?

Low power consumption is the reasen why OLED is a better choice for portable devices. It also makes OLEDs, and a candidate to be the white-light "bulb" of the future Greater brightness.

Light sources based on organic electroluminiscent materials offer the potential to make a high light intensity possible at a low energy consumption on mechanically flexible substrates." said project head Prof. Dr. Karl Leo (IAPP) about the high expectations.

- The Flat screen are brighter, and have a fuller viewing angle. Better durability - OLED-Displays can operate in a temperature range Lighter weight - the screen can be made very thin, and can be 'printed' on flexible surfaces.

Organic light emitting diodes consist of stacks of organic layers (thickness about 100 nm), which are inserted between a cathode and an anode. Usually, the substrate is glass coated with a transparent conductive oxide being the anode, followed by the organic stack, consisting of hole transport and electron transport materials, followed
by the inorganic cathode. Key advantages of the organic luminescence are the chemical variability of the organic light-emitting diodes, allowing virtually any color including white, and the thin film system, allowing large-area and low-cost deposition, and the possibility to use thin and even flexible substrates to realize a novel class of lighting and display solutions not possible for other technologies.

Types of OLEDs:

There are several types of OLEDs:

Passive-matrix OLED

Active-matrix OLED

Transparent OLED

Top-emitting OLED

Foldable OLED

White OLED

Each type has different uses.

Conclusion & near future with OLED

Research and development in the field of OLEDs is proceeding rapidly and may lead to future applications in heads-up displays, automotive dashboards, billboard-type displays, home and office lighting and flexible displays. A device with an OLED display could change information almost in real time. Video images could be much more realistic and constantly updated. The newspaper of the future might be an OLED display that refreshes with breaking news and like a regular newspaper, you could fold it up when you're done reading it and stick it in your backpack or briefcase.