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OLed seminar synopsis


1. INTRODUCTION- Organic light emitting diodes (OLEDs) are optoelectronic 
devices based on small molecules or polymers that emit light when an 
electric current flows through them. Simple OLED consists of a 
fluorescent organic layer sandwiched between two metal electrodes. Under 
application of an electric field, electrons and holes are injected from 
the two electrodes into the organic layer, where they meet and 
recombine to produce light. They have been developed for applications 
in flat panel displays that provide visual imagery that is easy to 
read, vibrant in colors and less consuming of power. 
OLEDs are light weight, durable, power efficient and ideal for 
portable applications
 An OLED is a solid-state semiconductor device that is 100 to 500 nanometers thick or about 200 times smaller than a human hair.
 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 (PMOLED) or active addressing schemes. Active-matrix OLEDs (AMOLED) require a thin-film transistor backplane to switch each individual pixel on or off, but allow for higher resolution and larger display sizes.
An OLED display works without a backlight. Thus, it can display deep black levels and can be thinner and lighter than a liquid crystal display (LCD). In low ambient light conditions such as a dark room an OLED screen can achieve a higher contrast ratio than an LCD, whether the LCD uses cold cathode fluorescent lamps or LED backlight.
OLEDs can replace the current technology in many applications due to following performance advantages over LCDs.
·         Greater brightness 
·         Faster response time for full motion video 
·         Fuller viewing angles 
·         Lighter weight 
·         Greater environmental durability 
·         More power efficiency 
·         Broader operating temperature ranges 
·         Greater        cost-effectiveness
 



2. MAKING OF OLEDs
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.OLEDs are organic because they are made from carbon and hydrogen. There's no connection to organic food or farming - although OLEDs are very efficient and do not contain any bad metals - so it's a real green technology.
An OLED consists of the following parts:
Substrate (clear plastic, glass, foil) - The substrate supports the OLED.
Anode (transparent) - The anode removes electrons (adds electron "holes") when a current flows through the device.
Organic layers - These layers are made of organic molecules or polymers.
Conducting layer - This layer is made of organic plastic molecules that transport "holes" from the anode. One conducting polymer used in OLEDs is polyaniline.
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.
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
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