ORGANIC LIGHT EMITTING

DIODE(O.L.E.D.)

PRESENTED BY :-

MOHAMMAD HAMMAD AHMAD (2K12/EE/080)DEPARTMENT OF ELECTRICAL ENGINEERING DELHI TECHNOLOGICAL UNIVERSITY , NEW DELHI-110042

WHAT IS A L.E.D. ?

L.E.D. OR LIGHT EMITTING DIODE IS A SEMICONDUCTOR LIGHT

SOURCE THAT WORKS ON THE PRINCIPLE OF

ELECTROLUMINESCENCE WHICH IS A RESULT OF RADIATIVE

RECOMBINATION OF ELECTRONS AND HOLES IN A MATERIAL.

STRUCTURE AND WORKING

LED CONSISTS OF A CHIP OF

SEMICONDUCTING MATERIAL DOPED

WITH IMPURITIES TO CREATE A P-N

JUNCTION. AS IN OTHER DIODES,

CURRENT FLOWS EASILY FROM THE P-

SIDE, OR ANODE, TO THE N-SIDE, OR

CATHODE, BUT NOT IN THE REVERSE

DIRECTION. CHARGE-CARRIERS—

ELECTRONS AND HOLES—FLOW INTO

THE JUNCTION FROM ELECTRODES WITH

DIFFERENT VOLTAGES. WHEN AN

ELECTRON MEETS A HOLE, IT FALLS

INTO A LOWER ENERGY LEVEL AND

RELEASES ENERGY IN THE FORM OF A

PHOTON.

ADVANTAGES AND DISADVANTAGES

ADVANTAGES

1.LEDS CONSUME LESSER POWER AS COMPARED TO NORMAL

INCANDESCENT LIGHTS.

2.LEDS HAVE LONGER LIFETIME.

3.LEDS HAVE LESSER RESPONSE TIME.

4.LEDS RADIATE LESS HEAT.

5.LEDS CAN EMIT LIGHT OF ANY COLOR USING SPECIFIC FILTER.

6.LEDS CAN BE OF VERY SMALL SIZE .

7.AND MANY MORE……

1.LEDs are expensive.

2.LEDs are temperature dependent and their performance

is affected by temperature to a very large extent.

3.LEDs works between certain voltage and current ranges.

4.LEDs works only when they are connected with correct

electrical polarity.

DISADVANTAGES

THERE ARE MANY USES OF L.E.D.S IN PRESENT TIME FEW OF WHICH ARE :-

1.VISUAL SIGNALS WHERE LIGHT GOES MORE OR LESS DIRECTLY FROM THE SOURCE TO THE HUMAN EYE, TO CONVEY A MESSAGE OR MEANING.

2.ILLUMINATION WHERE LIGHT IS REFLECTED FROM OBJECTS TO GIVE VISUAL RESPONSE OF THESE OBJECTS.

3.MEASURING AND INTERACTING WITH PROCESSES INVOLVING NO HUMAN VISION.

4.NARROW BAND LIGHT SENSORS WHERE LEDS OPERATE IN A REVERSE-BIAS MODE AND RESPOND TO INCIDENT LIGHT, INSTEAD OF EMITTING LIGHT.

5.EMITTING WIRELESS INTERNET SIGNAL CALLED LI-FI.

6.LEDS CAN ALSO BE USED WITH CONTACT LENSES OR NORMAL EYE GLASSES MOST RECENT EXAMPLE IS GOOGLE GLASS.

7.THE LIGHT FROM LEDS CAN BE MODULATED VERY QUICKLY SO THEY ARE USED EXTENSIVELY IN OPTICAL FIBER AND FREE SPACE OPTICS COMMUNICATIONS.

Applications

WHAT IS AN O.L.E.D.STRUCTURE,MANUFACTURING AND WORKING

An OLED (organic light-emitting diode) is a light-emitting diode (LED) in which the emissiveelectroluminescent layer is a film of organic compound which emits light in response to an

electric current.

. This layer of organic semiconductor is situated between two electrodes. Generally, at least one of these electrodes is transparent. OLEDs are used to create digital displays in devices such as television screens, computer monitors, portable systems such as mobile phones, handheld games consoles and PDAs. A major area of research is the development of white OLED devices for use in solid-state lighting applications.

HISTORY AND DEVELOPMENT

THE FIRST OBSERVATIONS OF ELECTROLUMINESCENCE IN ORGANIC MATERIALS WERE

IN THE EARLY 1950S BY ANDRÉ BERNANOSE AND CO-WORKERS AT THE NANCY-

UNIVERSITÉ, FRANCE.

THEY APPLIED HIGH-VOLTAGE ALTERNATING CURRENT (AC) FIELDS IN AIR TO

MATERIALS SUCH AS ACRIDINE ORANGE, EITHER DEPOSITED ON OR DISSOLVED IN

CELLULOSE OR CELLOPHANE THIN FILMS.

IN 1960, MARTIN POPE AND CO-WORKERS AT NEW YORK UNIVERSITY DEVELOPED

OHMIC DARK-INJECTING ELECTRODE CONTACTS TO ORGANIC CRYSTALS. THEY

FURTHER DESCRIBED THE NECESSARY ENERGETIC REQUIREMENTS (WORK FUNCTIONS)

FOR HOLE AND ELECTRON INJECTING ELECTRODE CONTACTS.

ALSO IN 1965, W. HELFRICH AND W. G. SCHNEIDER OF THE NATIONAL RESEARCH

COUNCIL IN CANADA PRODUCED DOUBLE INJECTION RECOMBINATION

ELECTROLUMINESCENCE FOR THE FIRST TIME IN AN ANTHRACENE SINGLE CRYSTAL

OF MODERN DOUBLE INJECTION DEVICES.

IN THE SAME YEAR, DOW CHEMICAL RESEARCHERS PATENTED A

METHOD OF PREPARING ELECTROLUMINESCENT CELLS USING HIGH

VOLTAGE (500–1500 V) AC-DRIVEN (100–3000 HZ) ELECTRICALLY

INSULATED ONE MILLIMETRE THIN LAYERS OF A MELTED PHOSPHOR

CONSISTING OF GROUND ANTHRACENE POWDER, TETRACENE, AND

GRAPHITE POWDER.

WORKING PRINCIPLE

OLED Components

Like an LED, an OLED is a solid-state semiconductor device that is 100 to 500 nanometers thick

or about 200 times smaller than a human hair. OLEDs can have either two layers or three layers

of organic material,the third layer helps transport electrons from the cathode to the emissive

layer. Thus, the organic material must serve all the three main functions: electron

transport, hole transport and emission. The injection rates of both carriers should be almost

equal for high efficiency. Otherwise, the surplus electrons or holes will not recombine, which

results in low operation efficiency

An OLED consists of the following parts:

1. 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.

2. 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.

3. 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 ismade. One polymer used in the emissive layer is polyfluorene.

4. 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:

1. 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.

2. 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.

3. 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.

MANUFACTURING TECHNIQUE

MATERIALS USED

1.POLYMER(S)

POLYMER LIGHT-EMITTING DIODES

(PLED), ALSO LIGHT-EMITTING POLYMERS

(LEP), INVOLVE AN ELECTROLUMINESCENT

CONDUCTIVE POLYMER THAT EMITS

LIGHT WHEN CONNECTED TO AN

EXTERNAL VOLTAGE. THEY ARE USED AS A

THIN FILM FOR FULL-SPECTRUM COLOUR

DISPLAYS. POLYMER OLEDS ARE QUITE

EFFICIENT AND REQUIRE A RELATIVELY

SMALL AMOUNT OF POWER FOR THE

AMOUNT OF LIGHT PRODUCED.

TYPICAL POLYMERS USED IN PLED

DISPLAYS INCLUDE DERIVATIVES OF

POLY(P-PHENYLENE VINYLENE) AND

1.PHOSPHORESCENT MATERIALS

PHOSPHORESCENT ORGANIC LIGHT EMITTING DIODES USE THE

PRINCIPLE OF ELECTROPHOSPHORESCENCE TO CONVERT

ELECTRICAL ENERGY IN AN OLED INTO LIGHT IN A HIGHLY

EFFICIENT MANNER, WITH THE INTERNAL QUANTUM

EFFICIENCIES OF SUCH DEVICES APPROACHING 100%.

TYPICALLY, A POLYMER SUCH AS POLY(N-VINYLCARBAZOLE) IS

USED AS A HOST MATERIAL TO WHICH AN ORGANOMETALLIC

COMPLEX IS ADDED AS A DOPANT. IRIDIUM COMPLEXES SUCH

AS IR(MPPY)3.

3.FLUOROSCENT

THESE TYPE OF ORGANIC L.E.D.S HAVE FLOUROSCENT

MATERIAL AS THEIR MAIN CONSTITUENT AND THESE TYPE

OF ORGANIC LIGHT EMITTING DIODES ARE THE MOST

WIDELY USED ONES.

EXAMPLE:- PERYLENE

4. SMALL MOLECULE OLED

MOLECULES COMMONLY USED IN OLEDS INCLUDE

ORGANOMETALLIC CHELATES (FOR EXAMPLE ALQ3,

USED IN THE ORGANIC LIGHT-EMITTING DEVICE

REPORTED BY TANG ET AL.),

FLUORESCENT AND PHOSPHORESCENT DYES AND

CONJUGATED DENDRIMERS.

A NUMBER OF MATERIALS ARE USED FOR THEIR

CHARGE TRANSPORT PROPERTIES, FOR EXAMPLE

TRIPHENYLAMINE AND DERIVATIVES ARE COMMONLY

USED AS MATERIALS FOR HOLE TRANSPORT LAYERS.

FLUORESCENT DYES CAN BE CHOSEN TO OBTAIN

LIGHT EMISSION AT DIFFERENT WAVELENGTHS, AND

COMPOUNDS SUCH AS PERYLENE, RUBRENE AND

QUINACRIDONE DERIVATIVES ARE OFTEN USED.

ON THE BASIS OF PIXEL CONTROL/DRIVING

METHOD

1. A.M.O.L.E.D.-IN A.M.O.L.E.D. OR ACTIVE MATRIX

ORGANIC LIGHT EMITTING DIODE THE PIXELS ARE

CONTROLLED DIRECTLY.THIS TECHNIQUE IS USED

TO MAKE LARGER AND MORE EFFICIENT DISPLAYS

BUT IS EXPENSIVE.

2. P.M.O.L.E.D.-IN P.M.O.L.E.D. OR PASSIVE MATRIX

ORGANIC LIGHT EMITTING DIODE THE DISPLAY IS

CONTROLLED BY SWITCHING A CERTAIN ROW AND

COLUMN - IN EFFECT LIGHTING THE PIXEL AT THE

INTERSECTION. THE PIXELS ARE TURNED ON AND

OFF QUICKLY, AND THE SEQUENCE CREATES THE

IMAGE. BUT IT ONLY ALLOW FOR SMALL SIZED

DISPLAYS (UP TO 3", TYPICALLY) AND IS CHEAP.

Classification

ON BASIS OF DIRECTION LIGHT EXITS O.L.E.D.

1. TOP EMISSION- . TOP EMISSION DEVICES ARE CLASSIFIED BASED ON WHETHER OR

NOT THE LIGHT EMITTED FROM THE OLED DEVICE EXITS THROUGH THE LID THAT IS

ADDED FOLLOWING FABRICATION OF THE DEVICE. TOP-EMITTING OLEDS ARE

BETTER SUITED FOR ACTIVE-MATRIX APPLICATIONS AS THEY CAN BE MORE EASILY

INTEGRATED WITH A NON-TRANSPARENT TRANSISTOR BACKPLANE.

2. BOTTOM EMISSION-. OLED DEVICES ARE CLASSIFIED AS BOTTOM EMISSION DEVICES

IF LIGHT EMITTED PASSES THROUGH THE TRANSPARENT OR SEMI-TRANSPARENT

BOTTOM ELECTRODE AND SUBSTRATE ON WHICH THE PANEL WAS MANUFACTURED.

ON BASIS OF MANUFACTURING MATERIAL

1. SMALL MOLECULE-SMALL MOLECULES' OLEDS ARE MORE

COMMON TODAY, WITH MOST DISPLAYS USING THOSE KIND

OF MATERIALS.THIS TYPE OF O.L.E.D. IS DIFFICULT TO

FABRICATE.

2. LARGE MOLECULE/POLYMER BASED-LARGE MOLECULES

(ALSO CALLED POLYMER-BASED OLEDS, OR P-OLEDS) ARE

LAGGING BEHIND IN LIFETIME AND EFFICIENCY SPECS. P-

OLEDS MIGHT BE EASIER TO MAKE, THOUGH, BECAUSE THEY

ARE MORE EASILY ADAPTED FOR PRINTING.

3. FLOURSCENT O.L.E.D.-THESE TYPE OF O.L.E.D.S HAS

FLUORESCENT MATERIAL AS MAJOR CONSTITUENT.THESE

ARE THE MOST USED O.L.E.D.S.

4. PHOSPHORESCENT O.L.E.D.-THESE O.L.E.D.S HAS

PHOSPHORESCENT MATERIAL AS MAJOR CONSTITUENT

.THEY ARE KNOWN TO GIVE A MORE EFFICIENT PICTURE.

SOME OTHER O.L.E.D.

1. FOLDABLE O.L.E.D.S-SUBSTRATE IS MADE OF FLEXIBLE

METALLIC FOILS OR PLASTICS. THEY ARE LIGHTWEIGHT

AND CONSIDERED VERY DURABLE.

2. TRANSPARENT O.L.E.D.S-USE TRANSPARENT OR SEMI-

TRANSPARENT CONTACTS ON BOTH SIDES TO CREATE

DISPLAYS THAT CAN BE TOP AND BOTTOM EMITTING.

OFFERS GREAT CONTRAST.

3. STACKED O.L.E.D.-UNIQUE PIXEL ARCHITECTURE THAT

STACKS RED, GREEN, AND BLUE SUBPIXELS ON TOP OF

ONE ANOTHER (INSTEAD OF NEXT TO EACH ANOTHER).

THIS PROVIDES BETTER COLOR SCOPE AND DEPTH, AND

ALSO REDUCES PIXEL GAP

DIFFERENCE BETWEEN LCD,PLASMA AND OLED DISPLAYS

APPLICATIONSORGANIC LIGHT EMITTING DIODES HAVE A LOT OF

PRACTICAL APPLICATIONS IN TODAY`S WORLD.SOME OF

WHICH ARE AS FOLLOW…..

THE MOST WIDE USE OF ORGANIC L.E.D.S IS IN THE

FIELD OF DISPLAYS OR MORE PRECISELY VDUS(VISUAL

DISPLAY UNITS) SUCH AS MONITORS , TELEVISIONS ,

MOBILE PHONES ETC. O.L.E.D. SCREENS HAVE A MUCH

GOOD DISPLAY RESOLUTION THAN NORMAL LCD(LIQUID

CRYSTAL DISPLAY) AND ALSO HAVE A LONGER LIFETIME

AS COMPARED TO CRT(CATHODE RAY TUBE) DISPLAYS

OR LCD.

ORGANIC LEDS CAN ALSO BE USED IN THE

CONSTRUCTION OF WEARABLE ELECTRONICS.

ADVANTAGES• SUBSTRATE IS FLEXIBLE, WHICH OFFERS THE POSSIBILITY OF NEW

DISPLAY OPTIONS

• PLASTIC CAN BE USED AS OPPOSED TO GLASS, WHICH IS GOOD BECAUSE

GLASS ABSORBS SOME LIGHT

• SINCE MANUFACTURERS ARE WORKING MOSTLY WITH PLASTICS, OLEDS

TEND TO BE EASIER TO PRODUCE

• WIDER VIEWING RANGE (APPROXIMATELY 170°)

• MUCH BETTER COLOR BALANCE BECAUSE MORE THAN 16 MILLION CAN

BE DISPLAYED.

• NO PROBLEM TO OBSERVE FROM A HIGH ANGLE (AROUND 160°), WHICH MEANS

BETTER READABILITY FROM DIFFERENT POSITIONS.

• CLEAR AND BRIGHT IMAGE.

• MORE MECHANICALLY RESISTANT - IDEAL FOR POCKET COMPUTERS AND

MOBILE PHONES.

• FAST RESPONSE.

• LOW ENERGY CONSUMPTION.

• WELL READABLE IN CASE OF DIRECT DAYLIGHT.

• POSSIBILITY TO BEND OR SHAPE THE DEVICES.

• ADDITIONAL SOURCE OF LIGHT IS NOT NEEDED SO THEY ARE THINNER AND

LIGHTER.

DISADVANTAGESDESPITE OF BEING VERY MUCH ADVANTAGEOUS OLEDS ALSO HAVE

SOME DISADVANTAGE WHICH ARE..

• WATER CAN DAMAGE THE DEVICE AND LIMIT FLEXIBILITY

• DISPLAYS CAN BE DAMAGED BY PROLONGED EXPOSURE TO UV LIGHT

• PIXEL BRIGHTNESS FADES OVER TIME AND THE VARIED LIFESPAN OF

THE DYES CAN CAUSE A DISCREPANCY BETWEEN RED, GREEN, AND

BLUE INTENSITY; THIS COULD, IN TURN, LEAD TO SCREEN BURN-IN.

• BLUE OLEDS ARE INEFFICIENT: RED (625 NM) AND GREEN (530 NM)

DIODES HAVE SHOWN EXTERNAL QUANTUM EFFICIENCY VALUES OF

20% AND 19%; BLUE DIODES (430 NM), ON THE OTHER HAND, ARE

MUCH LOWER, WITH A REPORTED MAXIMUM EXTERNAL QUANTUM

VALUE BETWEEN 4% AND 6%

FUTURE SCOPETHE FUTURE OF ORGANIC LIGHT EMITTING

TECHNIQUE IS VERY “BRIGHT” INDEED AS DESPITE OF

PRODUCING A VERY CLEAR AND BRIGHT IMAGE THIS

TECHNIQUE ALSO HAS THE ABILITY OF PRODUCING

FLEXIBLE AS WELL AS TRANSPARENT DISPLAYS WHICH

CAN BE USED IN MANY FUTURE APPLICATIONS.

BEING FLEXIBLE ORGANIC LIGHT EMITTING DIODES

CAN ALSO BE INCORPORATED IN MANUFACTURING

WEARABLE ELECTRONICS ,SUCH AS PEBBLE WATCH.

THIS TECHNIQUE CAN ALSO BE USED TO MAKE MORE

EFFICIENT TOUCHSCREEN DISPLAYS AS IN

SMARTPHONES,

ONE OF THE MOST IMPORTANT USE OF THIS

TECHNIQUE IS IN MANUFACTURE OF TRANSPARENT

SCREENS FOR TELEVISIONS ,MONITORS AND