POLYMER DIODES

POLYMER LED’S

SOME POLYMERS CONDUCT ELECTRICITY AND EMIT LIGHT

THESE SEMICONDUCTING POLYMERS ARE NOW EXTENSIVELY USED IN MARKETS

STRUCTURE

CONSISTING OF A SERIES OF LAYERS- ELECTRODES, ACTIVE SEMICONDUCTOR MATERIAL, INSULATORS AND SO ON

AND IT IS ATTRACTIVE IF THEY CAN BE ASSEMBLED, AS POLYMERS CAN BE

BONDING FEATURES

ALTERNATE SINGLE AND DOUBLE CARBON –CARBON BONDS

MATERIALS ARE SAID TO BE CONJUGATED

C=C FORMED WHEN TWO OF THREE 2P ORBITALS ON EACH CARBON ATOM COMBINE WITH 2S ORBITALS FORMING SP2 HYBRID

FORMATION OF THREE SIGMA MOLECULAR ORBITALS TAKE PLACE

THIRD P ORBITAL FORMS A PAIR OF π MOLECULAR ORBITALS THAT ARE SPREAD OUT IR DELOCALIZED OV ER A POLYMER CHAIN

THE LOWER π-BONDING FORMS VALENCE BAND WHILE THE ANTIBONDING FORMS THE CONDUCTION BAND.

BONDING BASICS

THIS ‘BAND GAP’ GIVES THE POLYMER SEMICONDUCTING NATURE

STRUCTURE

CONTD..

MOST CONJUGATED POLYMERS HAVE A SEMICONDUCTOR BAND GAPS OF 1.5-3eV.

WELL SUITED FOR OPTOELECTRONIC DEVICES.

MOST WIDELY USED POLYMER

PPV- POLY PHENYLENE VINYLENE HAVING A BAMD GAP OF 2.5eV EMITS YELLOW GREEN LIGHT

IT IS MADE UP OF BENZENE RINGS – PHENYLENE UNITS- LINKED TO ONE ANOTHER VIA TWO CARBONS, WHICH ARE ALSO BOUNDED TO A SINGLE HYDROGEN ATOM.

THE PHENYLENE VINYLENE UNIT

PLED STRUCTURES

FIRST IT WAS MADE USING A THIN LAYER OF POLYMER SANDWICHED BETWEEN A PAIR OF ELECTRODES

NEGATIVE ELECTRODE INJECTS ELECTRONS INTOMPOSITIVER FILM

POSITIVE ELECTRODES INJECTS HOLES

CONTINUED..

AN ELECTRON AND HOLE CAPTURE ONE ANOTHER WITHIN THE POLYMER AND THEY FORM A NEUTRAL ‘ÉXCITON’

IT IS A BOUND EXCITED STATE THAT CAN DECAY BY EMITTING A PHOTON

THE PROCESS IS KNOWN AS ELECTROLUMINESCENCE SINCE EMISSION IS CAUSED BY ELECTRIC FIELD BETWEEN THE ELECTRODES.

CONTD..

NEGATIVE ELECTRODE SHOULD HAVE LOW WORK FUNCTION SO THAT ELECTRONS CAN BE EASILY INJECTED

POSITIVE ELECTRODE SHOULD HAVE HIGH WORK FUNCTION TO SUCK IN ELECTRONS FROM THE POLYMER

HOLE INJECTING ELECTRODE- MADE OF INIDIUM-TIN OXIDE.

PEDOT /PSS LAYER

EXTRA LAYER WHICH IMPROVES THE INJECTION OF HOLES

PEDOT- POLY (ETHYLENEDIOXY) THIOPHENE

IT IS MIXED WITH POLSTYRENE SULPHONIC ACID (PSS) TO FORM A STABLE AND HIGHLY CONDUCTING CHARGE TRANSFER PLEX

IT IS DEPOSITED ON AQUEOUS SOLUTION TO FORM A LAYER ON INIDIUM TIN OXIDE

PEDOT-PSS LAYERING

USES OF POLYMER LED’S

BACK LIGHTS FOR MOBILE PHONES PORTABLE ELECTRONIC PRODUCTS GRAPHIC DISPLAYS- TELEVISION

SCREENS, COMPUTER MONITORS, PALM TOP DEVICES

LAB-ON-A CHIP DEVICE COULD BE USED IN HOSPITALS

DIRECT PRINTING- INK JET PRINTING OLED’S

USES

PORTABLE ELECTRONIC PRODUCTS

USES

GRAPHIC DISPLAYS- TELEVISION SCREENS, COMPUTER MONITORS, PALM TOP DEVICES

USES

DIRECT PRINTING- INK JET PRINTING

USES

OLED- ORGANIC LIGHT EMITTING DIODES

DISPLAY SYSTEMS OF PLED

CONCLUSION

PLED’S ARE OF IMMENSE IMPORTANCE AND THEIR USAGE CARRIES A SIGNIFICANCE IN PRESENT DAY TECHNOLOGICAL ADVANCEMENTS.

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