This document discusses electroluminescence and the polymer polyparaphenylene vinylene (PPV). It explains that PPV is a conducting polymer that emits bright yellow fluorescence, making it suitable for applications in light-emitting diodes and photovoltaic devices. PPV was used in the first polymer light-emitting diode and is still used in organic light-emitting diodes (OLEDs) due to its stability and optical properties. OLEDs use a layer of organic material like PPV between electrodes that emits light when electric current is applied.

1. Electroluminescent Polymer-
Polyparaphenelene vinylene
-Pushkar Badgujar
-FE 2
-1244

2. What we plan to learn
1. What is Electroluminescence?
2. Basic principles and working .
3. PPV(Polyparaphenylene vinylene)
4. Applications
5. Specific Example(OLED)

3. Electroluminescence
• Electroluminescence (EL) is an optical phenomenon and electrical phenomenon in
which a material emits light in response to the passage of an electric current or to a
strong electric field.
• Textbook defn. “ The property in which a material produces bright light of different colours
when stimulated electronically is known as electroluminesence. The material which shows
electroluminescence,is called as electroluminescent material. ”
• Examples of electroluminescent materials:
1.Electroluminescent devices are fabricated using either organic or inorganic
electroluminescent materials. The active materials are generally semiconductors of wide
enough bandwidth to allow exit of the light.
2.The most typical inorganic thin-film EL (TFEL) is ZnS:Mn with yellow-orange emission.
Examples of the range of EL material include:
3.Powdered zinc sulfide doped with copper (producing greenish light) or silver (producing
bright blue light)
4.Thin-film zinc sulfide doped with manganese (producing orange-red color)
5.Naturally blue diamond, which includes a trace of boron that acts as a dopant.
6.Semiconductors containing Group III and Group V elements, such as indium phosphide
(InP), gallium arsenide (GaAs), and gallium nitride (GaN).
7.Certain organic semiconductors, such as [Ru(bpy)3]2+(PF6-)2, where bpy is 2,2'-bipyridine

4. PPV(Polyparaphenylene vinylene)
• Poly(p-phenylene
vinylene) (PPV, or polyph
enylene vinylene) is
a conducting polymer.
• PPV is the only polymer of
this type that has so far been
successfully processed into a
highly ordered crystalline
poly(1,4-phenylene-1,2-
thin film.
ethenediyl) • PPV is easily synthesized in
good purity and high
molecular weight.

5. • Although insoluble in water, its
precursors(a precursor is a compound that
participates in the chemical reaction that produces
another compound.) can be manipulated in aqueous
solution.
•The small optical band gap and its bright yellow
fluorescence makes PPV a candidate in many electronic
applications such as light-emitting diodes (LED) and
photovoltaic devices.
• Moreover, PPV can be easily doped to form electrically
conductive materials.
•Its physical and electronic properties can be altered by
the inclusion of functional side groups.

6. Manufacture of PPV
• PPV can be synthesized by Wittig-type couplings between the bis(ylide)
derived from an aromatic bisphosphonium salt and dialdehyde, especially
1,4-benzenedialdehyde.
• Textbook method employs the use of a precursor polymer poly -n-octyl
sulphinyl paraphenylene ethylene by heating it in vacuum. Elimination of
n-octylthiol introduces the double bonds in the chain.
reaction as follows :

7. Properties and Structure
• PPV is a diamagnetic material and has a very low intrinsic electrical
conductivity, on the order of 10-13 S/cm.
• The electrical conductivity increases upon doping with iodine, ferric
chloride, alkali metals, or acids. However, the stability of these doped
materials is relatively low. In general, unaligned, unsubstituted PPV
presents only moderate conductivity with doping.
• Alkoxy-substituted PPVs are generally easier to oxidize than the parent
PPV and hence have much higher conductivities. Longer side chains lower
the conductivity and hinder interchain hopping of charge carriers.

8. Applications Of PPV
• Due to its stability, processability, and electrical and
optical properties, PPV has been considered for a
wide variety of applications.[1] In 1989 the first
polymer-based light emitting diode (LED) was
discovered using PPV as the emissive layer.
• Polymers are speculated to have advantages over
molecular materials in LEDs, such as ease of
processing, reduced tendency for crystallization, and
greater thermal and mechanical stability. Ever since
the first breakthrough in 1989, a large number of
PPV derivatives have been synthesized and used for
LED applications.

9. •Although solid-state lasing has yet to be demonstrated in
an organic LED, poly[2-methoxy-5-(2’-ethylhexyloxy)-p-
phenylene vinylene] (MEH-PPV) has been proven to be a
promising laser dye due to its high fluorescence efficiency
in solution.
•Polyphenylene vinylene is capable
of electroluminescence, leading to applications in
polymer-based organic light emitting diodes. PPV
was used as the emissive layer in the first polymer
light-emitting diodes.Devices based on PPV emit
yellow-green light, and derivatives of PPV obtained
by substitution are often used when light of a
different color is required.

10. • . In presence of even a small amount
of oxygen, singlet oxygen is formed during
operation, by energy transfer from the excited
polymer molecules to oxygen molecules. These
oxygen radicals then attack the structure of the
polymer, leading to its degradation. Special
precautions therefore have to be kept during
manufacturing of PPV in order to prevent
oxygen contamination.
• PPV is also used as an electron-donating
material in organic solar cells. Although PPV-
based devices suffer from poor absorption
and photodegradation, PPV and PPV derivatives
(especially MEH-PPV and MDMO-PPV) find
frequent application in research cells.

11. OLED (organic light-emitting diode)
• An OLED (organic light-emitting diode) is a light-emitting
diode (LED) in which the emissive electroluminescent layer is a film
oforganic compound which emits light in response to an electric current.
This layer of organic semiconductor material 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.
• An OLED display works without a backlight. Thus, it can display deep black
levels and can be thinner and lighter than a liquid crystal display (LCD). In
low ambient light conditions such as a dark room an OLED screen can
achieve a higher contrast ratio than an LCD, whether the LCD uses cold
cathode fluorescent lamps or LED backlight. Due to its low thermal
conductivity, an OLED typically emits less light per area .

12. Principle and Working(OLED)
• A typical OLED is composed of a layer of organic
materials situated between two electrodes, the anode
and cathode, all deposited on a substrate. The organic
molecules are electrically conductive as a result of
delocalization of pi electrons caused
by conjugation over all or part of the molecule.
• During operation, a voltage is applied across the
OLED such that the anode is positive with respect to
the cathode. A current of electrons flows through the
device from cathode to anode, as electrons are
injected into the LUMO of the organic layer at the
cathode and withdrawn from the HOMO at the anode.
This latter process may also be described as the
injection of electron holes into the HOMO.
Electrostatic forces bring the electrons and the holes
towards each other and they recombine forming
an exciton, a bound state of the electron and hole.
Schematic of a bilayer OLED: 1. Cathode (−), 2. Emissive This happens closer to the emissive layer, because in
(Polymer)Layer, 3. Emission of radiation, 4. Conductive
organic semiconductors holes are generally
Layer, 5. Anode (+)
more mobile than electrons. The decay of this excited
state results in a relaxation of the energy levels of the
electron, accompanied by emission
of radiation whose frequency is in the visible region.
The frequency of this radiation depends on the band
gap of the material, in this case the difference in
energy between the HOMO and LUMO.

13. Electroluminiscent polymers are the
future of the semiconductor and
display unit industry