08-09-2014, 02:10 PM
[u]LIGHT EMITTING POLYMERS[/u]
[attachment=67720]
INTRODUCTION
Light emitting polymers or polymer based light emitting diodes discovered by Friend et al in 1990 has been found superior than other displays like, liquid crystal displays (LCDs) vacuum fluorescence displays and electro luminescence displays.Though not commercialised yet, these have proved to be a mile stone in the filed of flat panel displays. Research in LEP is underway in Cambridge Display Technology Ltd (CDT), the UK.
In the last decade, several other display contenders such as plasma and field emission displays were hailed as the solution to the pervasive display. Like LCD they suited certain niche applications, but failed to meet broad demands of the computer industry.
Today the trend is towards the non crt flat
panel displays. As LEDs are inexpensive devices these can be extremely handy in constructing flat panel displays.
WHAT IS LEP ?
LEP is a polymer that emits light when a voltage is applied to it. The structure comprises a thin film semi conducting polymer sandwiched between two electrodes namely anode and cathode. When electrons and holes are injected from the electrodes, the recombination of these charge carriers takes place, which leads to emission of light that escape through glass substrate.
The ban gap, that is energy difference between valence band and conduction band of the semi conducting polymer determines the wave length, that is colour of the emitted light
CHEMISTRY BEHIND LEP
LEPs are constructed from a special class of polymers called conjugated polymers. Plastic materials with metallic and semiconductor characteristics are called conjugated polymers. These polymers posses delocalised pi electrons along the backbone, whose mobility shows properties of semiconductors. Also this gives it the ability to support positive and negative charge carriers with high mobility along the polymer chain.
The charge transport mechanism in conjugated polymers is different from traditional inorganic semiconductors. Theamorphous chain morphology results in inhomogeneous broadening of the energies of the chain segments and leads to hopping type transport.
Conjugated polymers have already found application as conductor in battery electrodes, transparent conductive coatings, capacitor electrolytes and through hole platting in PCB’s. There are fast displaying traditional materials such as natural polymers etc owing to better physical and mechanical properties and amenability to various processes
BASIC STRUCTURE AND WORKING
An LEP display solely consists of the polymer material manufactured on a substrate of glass or plastic and doesn’t require additional elements like polarizers that are typical of LCDs. LEP emits light as a function of its electrical operation.
The basic LEP consists of a stack of thin organic polymer layers sandwiched between a transport anode and a metallic cathode. Figure shows the basic structure. The indium-tin-oxide (ITO)coated glass is coated with a polymer. On the top of it, there is a metal electrode of Al, Li, Mg or Ag. When a bias voltage is applied, holes and electrons move into the polymer. These moving holes and electrons combine together to form hole electron pairs known as “excitons’. These excitons are in excited state and go back to their initial state by emitting energy.
MANUFACTURING
In order to manufacture the polymer two techniques are used.
Spin coating process
This technique involves spinning a disk, that is glass substrate at a fixed angular velocity and letting a small amount of polymer solution to drop on the top of the disk. It is shown in the figure. Spin coating machine used has a few thousands rotations
per minute.
The robot pours the plastic over the rotating plate, which in turn, evenly spreads the polymer on the plate. This results in an extremely fine layer of the polymer having a thickness of 100 nanometers.Once the polymer is evenly spread, it is a\baked in an oven to evaporate any remnant liquid
Stacked organic LEPs
They use pixel architecture and offers high-definition display resolution and true-colour quality for the next generations display applications. With this type, each pixel emits the desired colour and thus is perceived correctly, no matter what size it is and from where it is viewed
Flexible organic LEPs
They are built on flexible substrates instead of glass substrates. These materials provide the ability to conform, bend or roll a display into any shape. So these find application on They employ an innovative transparent contact to achieve an enhanced display. They can be top, bottom or both top and bottom emitting (transparent). Bi-directional LEPs will provide two independent displays emitting from opposite faces of the display. With portable products shrinking and desired information content expanding, transparent LEPs are a great way to double
the display area for the same display size
CONCLUSION
LEPs are promising, low cost solutions for today’s flat panel displays. Although not commercialised yet, these replace bulky and heavy CRT displays in the near future. However research is underway to improve the efficiency and lifetime of the polymer displays.
A panel of industry leaders predicted that LEP technology would storm the market in the near few years and we will find LEP in every sphere of life about ten years from now.
LEP technology is now set to change the products we use to view the world.
[attachment=67720]
INTRODUCTION
Light emitting polymers or polymer based light emitting diodes discovered by Friend et al in 1990 has been found superior than other displays like, liquid crystal displays (LCDs) vacuum fluorescence displays and electro luminescence displays.Though not commercialised yet, these have proved to be a mile stone in the filed of flat panel displays. Research in LEP is underway in Cambridge Display Technology Ltd (CDT), the UK.
In the last decade, several other display contenders such as plasma and field emission displays were hailed as the solution to the pervasive display. Like LCD they suited certain niche applications, but failed to meet broad demands of the computer industry.
Today the trend is towards the non crt flat
panel displays. As LEDs are inexpensive devices these can be extremely handy in constructing flat panel displays.
WHAT IS LEP ?
LEP is a polymer that emits light when a voltage is applied to it. The structure comprises a thin film semi conducting polymer sandwiched between two electrodes namely anode and cathode. When electrons and holes are injected from the electrodes, the recombination of these charge carriers takes place, which leads to emission of light that escape through glass substrate.
The ban gap, that is energy difference between valence band and conduction band of the semi conducting polymer determines the wave length, that is colour of the emitted light
CHEMISTRY BEHIND LEP
LEPs are constructed from a special class of polymers called conjugated polymers. Plastic materials with metallic and semiconductor characteristics are called conjugated polymers. These polymers posses delocalised pi electrons along the backbone, whose mobility shows properties of semiconductors. Also this gives it the ability to support positive and negative charge carriers with high mobility along the polymer chain.
The charge transport mechanism in conjugated polymers is different from traditional inorganic semiconductors. Theamorphous chain morphology results in inhomogeneous broadening of the energies of the chain segments and leads to hopping type transport.
Conjugated polymers have already found application as conductor in battery electrodes, transparent conductive coatings, capacitor electrolytes and through hole platting in PCB’s. There are fast displaying traditional materials such as natural polymers etc owing to better physical and mechanical properties and amenability to various processes
BASIC STRUCTURE AND WORKING
An LEP display solely consists of the polymer material manufactured on a substrate of glass or plastic and doesn’t require additional elements like polarizers that are typical of LCDs. LEP emits light as a function of its electrical operation.
The basic LEP consists of a stack of thin organic polymer layers sandwiched between a transport anode and a metallic cathode. Figure shows the basic structure. The indium-tin-oxide (ITO)coated glass is coated with a polymer. On the top of it, there is a metal electrode of Al, Li, Mg or Ag. When a bias voltage is applied, holes and electrons move into the polymer. These moving holes and electrons combine together to form hole electron pairs known as “excitons’. These excitons are in excited state and go back to their initial state by emitting energy.
MANUFACTURING
In order to manufacture the polymer two techniques are used.
Spin coating process
This technique involves spinning a disk, that is glass substrate at a fixed angular velocity and letting a small amount of polymer solution to drop on the top of the disk. It is shown in the figure. Spin coating machine used has a few thousands rotations
per minute.
The robot pours the plastic over the rotating plate, which in turn, evenly spreads the polymer on the plate. This results in an extremely fine layer of the polymer having a thickness of 100 nanometers.Once the polymer is evenly spread, it is a\baked in an oven to evaporate any remnant liquid
Stacked organic LEPs
They use pixel architecture and offers high-definition display resolution and true-colour quality for the next generations display applications. With this type, each pixel emits the desired colour and thus is perceived correctly, no matter what size it is and from where it is viewed
Flexible organic LEPs
They are built on flexible substrates instead of glass substrates. These materials provide the ability to conform, bend or roll a display into any shape. So these find application on They employ an innovative transparent contact to achieve an enhanced display. They can be top, bottom or both top and bottom emitting (transparent). Bi-directional LEPs will provide two independent displays emitting from opposite faces of the display. With portable products shrinking and desired information content expanding, transparent LEPs are a great way to double
the display area for the same display size
CONCLUSION
LEPs are promising, low cost solutions for today’s flat panel displays. Although not commercialised yet, these replace bulky and heavy CRT displays in the near future. However research is underway to improve the efficiency and lifetime of the polymer displays.
A panel of industry leaders predicted that LEP technology would storm the market in the near few years and we will find LEP in every sphere of life about ten years from now.
LEP technology is now set to change the products we use to view the world.