LIGHT EMITTING POLYMER

PRESENTED BY : SARATH KUMAR K

CONTENTS

Introduction What is LEP? Chemistry behind LEP Structure And Working Types of LEPs Manufacturing Advantages Limitations Applications Conclusions

INTRODUCTION

It’s a rapidly emerging technology for next generation flat panel displays

It promises thin , light weight emissive display with low drive voltage , low power consumption , high contrast , wide viewing angle and fast switching times

LEPs are inexpensive and consume much less power than any other flat panel display

One interesting application of these displays is electronic paper that can be rolled up like newspaper

Light emitting polymers are superiors than other displays like liquid crystal displays (LCDs),vacuum fluorescence displays and electroluminescence displays.

The technology uses a light-emitting polymer (LEP) that costs much less to manufacture and run than CRTs because the active material used is plastic.

WHAT IS LEP?

LEP is a polymer that emits light when 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 theses charge carriers takes place , which leads to emission of light that escape through glass substrate.

The first polymer LEPs used poly phinylene vinylene(PPV) as the emitting layer

The band gap determines the wave length and colour of emitted light

STRUCTURE AND WORKING

The basic LEP consists of a stack of thin organic polymer layers sandwiched between a transport anode and a metallic cathode.

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 These moving holes and electrons combine together to form hole-

electron pairs known as “excitons”

When this energy drop occurs light comes out from the device . this phenomenon is called electroluminescence

Indium-tin oxide is typically used for the anode

TYPES OF LEPs

Flexible organic LEPs Stacked organic LEPs Transparent organic LEPs

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. On helmet face shields , military uniforms , shirtsleeves and

automotive windshields

Stacked organic LEPs

They use pixel architecture and offers high-definition display resolution and true-colour quality for the next generations display applications

Each pixel emits the desired colour and thus is perceived correctly , no matter what size it is and from where it is viewed

Stacked organic light-emitting device

Transparent organic LEPs

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

Transparent LEPs are a great way to double the display area for the same display size

Toled Structure

MANUFACTURING

SPIN COATING PROCESS

This technique involve 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

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 nanometer.

: Spin Coating Process

INK JET PRINTING

Use of inkjet printing for PLED displays Red , green and blue polymer solutions are jetted into well

defined areas with an angle of flight deviation of less than 5 The film thickness uniformity may have to be better than +

2percentage

Printer Based Technique

ADVANTAGES

Require only 3.3 volt and have lifetime of more than 30,000 hours

Great power efficiency than all other flat panel displays No directional or blurring effects Can be viewed at any angle Glare free view up to 160 degree

Cost much less to manufacture and run than CRTs , because the active material used is plastic

Can scale from tiny device millimeters in dimension to definition device up to 5.1 meter in diameter

Fast switching speed , 1000 times faster than LCDs

LIMITATIONS

AGING OF LEP

One of the major barriers to the commercial development of LEP is its usefull lifetime The light intensity gradually decreases and some discrete regions become totally dark. This is called aging of LEP

The solution was to do the final soldering in a glass jar filled nitrogen

SPACE CHARGE EFFECT The effect of space charge on the voltage-current characteristics

and current-voltage characteristics becomes more pronounced when the difference in the electron hole mobilities is increased. This will decrease the luminescence and hence decreases the efficiency

APPLICATIONS

Multi or full colour cell phone displays Full colour high-resolution personal digital assistants Heads-up instrumentation for cars Lightweight wrist watches High definition televisions

Roll-up daily refreshable electronic newspapers Automobile light systems without bulbs Window/wall/partitions that double as computer screens Military uniforms Aircraft cockpit instrumentation panel a lot of others

PHOTOVOLTAICS

PHOTOVOLTAICS PLED technology can be used in reverse, to convert light into

electricity. Devices which convert light into electricity are called photovoltaic (PV) devices, and are at the heart of solar cells and light detectors

POLY LED TV

LEPs TVs are really thin - the Sony XEL-1 for example is just 3mm thick. The new prototypes by Sony are merely 0.3mm thick!

TRANSPARENT OLEDS

While there seem to be zero to few readily available uses of transparent OLEDs (TOLEDs) in the consumer market today, the technology exists for wide spread use in the future

NEWS AND INFORMATION

Imagine a day when you are reading a newspaper that is capable of showing pictures and video, is continuously updating itself with the latest news via Wi-Fi connection, and is also so thin and flexible that you can roll it up and put it in your backpack or briefcase.

“That day may someday be a reality thanks to OLED technology

OLED PASSPORT

Samsung SDI from Germany have designed the OLED passport which is claimed to be completely manipulation-proof.

The OLED display will be able to display both video and text containing information about the passport holder.

ADVANCEMENTS IN THE HOME

One of the many possibilities is to replace regular walls or windows with similar sized OLED installations which will “lead to user-definable window spaces".

These walls will use transparent OLEDs that will make it possible to have certain areas opaque while other areas clear, depending on what the homeowner would like. Additionally, “the wall can be any color or design that you want.

CONCLUSION

LEPs are promising , low cost solutions for today’s flat panel displays. Although not commercialized 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 display

Bibliography.

www. cdtltd.co.uk www. research.philips.com www. covion.com www.ieee.com D.Rwdinger, R.Farshchi and V.Subramanian. “Inkjet passive

component and plastic substrate”. 2003 IEEE Device Research conference digest pp.187-188, 2003

 Josephine B.Lee and Vivek Subramanian. “Ink Jet Passive devices” 2003 IEEE Device Research conference digest, 2003