LIGHT EMITTING
#1

Presented by
Shashanka Shekhar Pallai

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Introduction
 The LEP is an emissive technology about polymers that can emit light when a voltage is applied to it.
 It emits light under the application of electric field e.g.- polyvinyl chloride.
 The structure comprises of a thin film of semiconducting polymer sandwiched between two electrodes (cathode and anode).
Construction
 Light-emitting devices consist of active/emitting layers sandwiched between a cathode and an anode.
 Indium-tin oxides typically used for the anode and aluminum or calcium for the cathode.
 In order to manufacture the polymer, a spin-coating machine is used that has a plate spinning at the speed of a few thousand rotations per minute.
 Fig.2.1 (a) shows the structure of a simple single layer device with electrodes and an active layer.
Construction
 Fig.2.1(b) shows a symmetrically configured alternating current light-emitting (SCALE) device that works under AC as well as forward and reverse DC bias.
Ink jet Printing
 Although inkjet printing is well established in printing graphic images, only now are applications emerging in printing electronics materials.
 However, turning inkjet printing into a manufacturing process for PLED displays has required significant developments of the inkjet print head, the inks and the substrates (as in Fig.).
Active & Passive Matrix
 Many displays consist of a matrix of pixels, formed at the intersection of rows and columns deposited on a substrate.
 Each pixel is a light emitting diode such as a PLED, capable of emitting light by being turned on or off.
 Pixel displays can either by active or passive matrix.
 Active displays have transistors so that when a particular pixel is turned on it remains on until it is turned off.
 In passive matrix systems, each row and each column of the display has its own driver, and to create an image, the matrix is rapidly scanned to enable every pixel to be switched on or off as required
 Active displays are preferred, however it is technically challenging to incorporate so many transistors into such small a compact area.
 Passive matrix displays tend to be used mainly where cheap, simple displays are required.
Basic principle & Technology
 Polymer properties are dominated by the covalent nature of carbon bonds making up the organic molecule’s backbone.
 A single carbon-carbon bond is composed of two electrons being shared in overlapping wave functions.
 The bond formed by the overlap of these hybridized orbital's from two carbon atoms is referred to as a ‘sigma’ bond.
 The electrons have mobility, as do the holes generated by the absence of electrons through oxidation with a dopant like iodine.
How LEP works
 Electric field is applied between two electrodes.
 The electron are injected from cathode and holes from anode.
 The injected charges recombined & decay radiatively.
Light Emission
 Electric field is applied between two electrodes
 Electric field is applied between two electrodes
 Electric field is applied between two electrodes
 Electric field is applied between two electrodes
Comparison Table
Advantages & Disadvantages
Advantages:-

 Require only 3.3 volts and have lifetime of more than 30,000 hours.
 Low power consumption.
 Can be scaled to any dimension.
 Cost much less because the active material is plastic.
 Simple to use technology than conventional solid state LEDs and lasers.
 Very slim flat panel.
Disadvantages:-
 Vulnerable to shorts due to contamination of substrate surface by dust.
 Voltage drops.
 Mechanically fragile.
Applications
 Polymer light-emitting diodes can easily be processed into large-area thin films using simple and inexpensive technology.
PHOTOVOLTAICS:
(Digital clocks powered by polymer solar cells)
POLY LED TV:
MP3 PLAYER DISPLAY:

Another product on the market taking advantage of a thin form-factor, light-emitting polymer display is the new, compact, MP3 audio player.
BABY MOBILE:
This mobile uses light weight organic light emitting diodes to realize images and sounds in response to gestures and speech of the infant.
Future Developments
 High efficiency displays running on low power and economical to manufacture will find many uses in the consumer electronics field.
 Demands for information on the move could drive the development of 'wearable' displays, with interactive features.
Conclusion
 Major electronic firms such as Philips and pioneer and smaller companies such as CDT are betting that the future holds tremendous opportunity for low cost and surprisingly high performance offered by organic electronic devices.
 Color displays may eventually replace LCDs in laptop and even desktop computers.
 Organic electronics are already entering commercial world. Multicolor automobile stereo displays are now available from Pioneer Corp.
 The portable and light weight organic displays will soon cover our walls replacing the bulky and power hungry cathode ray tubes.
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