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This article is presented by:
K.SUMANTH
K.V.CHANUKYA

Organic Electro-Luminescence

Introduction:
An organic light emitting diode (OLED) is a light-emitting diode (LED) in which the emissive electroluminescent layer is a film of organic compounds which emits light in response to an electric current. This layer of organic semiconductor material is sandwiched between two electrodes. Generally, at least one of these electrodes is transparent.
OLEDs are used in television screens, computer monitors, small, portable system screens such as mobile phones and PDAs, watches, advertising, information and indication; they can also be used in light sources for general space illumination and in large-area light-emitting elements. Due to their comparatively early stage of development, they typically emit less light per unit area than inorganic solid-state based LEDs point-light sources.
An OLED display functions without a backlight. Thus, it can display deep black levels and can be thinner and lighter than established liquid crystal displays. Similarly, in low ambient light conditions such as dark rooms, an OLED screen can achieve a higher contrast ratio than an LCD screen using either cold cathode fluorescent lamps or the more recently developed LED backlight.
There are two main families of OLEDs. These are those based upon small molecules and those employing polymers. Adding mobile ions to an OLED creates a Light-emitting Electrochemical Cell or LEC, which has a slightly different mode of operation.
OLED displays can use either passive-matrix or active-matrix addressing schemes. Active-matrix OLEDs (AMOLED) require a thin-film transistor backplane to switch each individual pixel on or off, and can make higher resolution and larger size displays possible.
What is an OLED:
Organic Light Emitting Diode, or OLED, is a technology that uses carbon-based organic material in a process that converts electric energy into light. This light is used to illuminate the screen and produce the most astounding results ever seen on a Display.

Like an LED, 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. In this article, we'll be focusing on the two-layer design
How do OLEDs work?


An OLED is made by placing a series of organic thin films between two conductors. When electrical current is applied, a bright light is emitted. An OLED is made by placing a series of organic thin films between two conductors. When electrical current is applied, a bright light is emitted.
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.
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.

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.

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.
Transparent OLED :
Transparent OLEDs have only transparent components (substrate, cathode and anode) and, when turned off, are up to 85 percent as transparent as their substrate. When a transparent OLED display is turned on, it allows light to pass in both directions. A transparent OLED display can be either active- or passive-matrix. This technology can be used for heads-up displays.