of Ravishankar University–B, 35 (1), 1-8 (2022)
OLED: New Generation Display
Lokesh Kumar Sahua* and
aSchool of Studies in Electronics and Photonics, Pt. Ravishankar Shukla
University Raipur, Chhattisgarh
*Corresponding Author: email@example.com; firstname.lastname@example.org
[Received: 06 August 2021; Revised: 26 October 2021; Accepted: 15
Abstract: As time gets advanced multiple progressions have happened in
the field of display devices. In this field first came a small LED then after
CRT (Cathode Ray Tube) which is used in present days but due to its heaviness,
we do not carry it from one place to another. Then after came LCD (Liquid
Crystal Display), the problem of bulkiness and required large area overcome by
LCD, the only problem with LCD is that it cannot see a clear picture from
different angles. LCD is a lightweight and flexible plastic substrate. After
all these innovations OLED came and OLED beat all issues of LCD and CRT. OLED
is light and slim in design, it does not require any kind of backlight, OLEDs
are self-luminous. Polymers are using to fabricate OLEDs or unlike LCDs small
molecules in the flat panel zone. It has low power consumption (only 2-10
volts) also OLEDs has a wide viewing angle (up to 160 degrees). The
applications of OLEDs in electronics are on the increase on daily basis from
camera to cell phones to OLED televisions.
Keywords: Light Emitting Diode, Cathode Ray Tube and Liquid
Emitting Diode another innovation that depends on electroluminescence. OLED has
received a lot of attention over the world because this is the only display device
which is overcome all the problems related to past display devices. Basically,
OLED is an energy conversion device i.e., converts electrical energy to light
energy (Yan and Gao 2002, 101-106). OLED based on
electroluminescence. Electroluminescence is light emission from a solid through
which an electric current is passed. Unlike CRT (Cathode Ray Tube), the OLED
fabrication process is easy and devices are thinner and lighter. Also, unlike
LCD (Liquid Crystal Display), OLED has a different viewing angle and we don’t
need any type of backlight. So, the power consumption and drive voltage are
low. The first commercial OLED display was introduced by Pioneer Electronics as
the front panel of car stereo in 1997. In OLEDs, the layers are a type of flat
panel display created by sandwiching a layer of electroluminescent material
such as GaAs between two layers of electrons. OLEDs are used to create digital
displays in devices such as television screens, computers, portable systems
such as mobile phones etc. OLED displays can use either passive-matrix OLED (PMOLED)
or active-matrix (AMOLED) addressing schemes.
Organic Light Emitting Diode
The ‘OLED’ stands
for Organic Light Emitting Diode. An OLED is a solid-state device or electronic
device, a technology that uses LEDs in which the light is produced by organic
molecules. These Organic Light Emitting Diode are considered to be the world’s
best display panels. OLEDs displays are made by placing a series of organic
thin films between two conductors. When an electric current is applied, a
bright light is emitted. This is called electro phosphoresce, even with the
layered system, these systems are thin. In comparison to human hair, it is less
the 200 times or usually less than 500 nm. OLED doesn’t need any backlight and
it has more energy efficient. The substance-using in OLED emits Red, Green,
Blue or White light. In OLED we can see
any type of image from different angles(Shrinar 2005)
Figure 1 indicates
how a junction diode allows current to float when electrons (black dots) and
holes (white dots) move across the boundary between n-type (red) and p-kind
(blue) semiconductor material.
LED is an assembly
diode with an added feature: it emits light. Every time electrons fall. To
assemble, they jump into holes in the other side, release more energy than the
residue, and then emit a faster light bulb. All those flashes produce a dull,
continuous light that is illuminated by LEDs.
OLEDs work in the
same way on conventional diodes and LEDs, but instead of using n-type and
p-type semiconductors, they use organic molecules to produce electrons and
structure of an OLED
Simple OLED is
built in six different layers. Above and below are layers of protective glass
or plastic. Top layer is called the seal and the bottom layer is the substrate.
Between those layers, there is a negative terminal (sometimes called a cathode)
and a positive terminal (called anode). Finally, between the anode and the
cathode is a two-layer layer made of organic molecules called the emissive layer
(where light is produced, near the cathode) and the conductor layer (near the
anode). Here's what it all looks like:(Placeholder11-5)
How does this
sandwich of layers make light?
· To make OLED
light, we simply attach the voltage (potential difference) across the anode and
· As electricity
begins to flow, the cathode receives electrons from the power source and anode
loses them (or "finds holes," if you choose to view it that way).
· We now have a
situation where additional electrons cause the emissive layer to be badly
charged (similar to the n-type in the junction diode), while the conduction
layer is positive called (similar to type p items).
· Permitting holes
go much farther than bad electrons so cross the border from the transit layer
to the delivery layer. When a hole (lack of electrons) meets an electron, both
· objects erase and
release small explosions of energy in the form of a particle of light - photon,
in other words. This process is called recombination, and because it occurs
several times per second OLED emits continuous light as long as the gas
continues to flow.
Working of an OLED
Working of OLED is
similar to an LED, it's important that you first understand how a basic LED
works. An consists of two semiconductor materials, it is usually germanium and
silicon, one of which is n-type (negatively charged) and the other are p-type.
When you join these together you get an area where the electricity produced on
their junction. OLED works on the same principle but instead of n-type and
p-type they use organic molecules to release holes and electrons. During
operation, we applied voltage to the OLED such that the anode is positive with
respect to the cathode, where the anode is picked based upon the quality of
their optical transparency, electrical conductivity and chemical stability.
When a current electron flows, the cathode starts receiving electrons from the
source and the anode starts losing them. As a result of this, the emissive
layer starts becoming more negatively charged and the conductive layer becomes
more positively charged. This process may also be described as the injection of
electron holes into the HOMO (Highest Occupied Molecule’s orbit). Electrostatic
forces bring the electrons and the holes towards each other and they recombine
forming an exaction, bound state of electrons and holes. Recombination energy is released and the
molecule and the polymer segment in which the recombination occurs reaches an
excited state. When a DC bias is applied to the electrodes, the injected
electrons and holes can recombine in the organic layer and emit light of a certain
colour depending on the properties of the organic materials.(Patel, Patel and Vatalia 2018)
are different types of OLED available at the moment and all of them are
designed for a different aim: types are below.
Passive Matrix OLEDs (PMOLEDs)
have strips of cathode, organic layers and strips of anode. Anode and cathode
strips are placed perpendicular to each other. The intersection of cathode and anode
make up the pixels where light is emitted. A current is applied to some strips
of cathode and anode to determine pixels whether on or off. Again, the
brightness of each pixel is proportional to the amount of applied current.
PMOLEDs are easy to produce, but they consume more power than other types of
OLEDs. However, power consumption is still less then LCDs and they are suitable
for text and icons for small screens (2 to 3 inches diagonal) such as those you
find in cell phones and MP3 players (Patel and Prajapati 2014).
AMOLEDs have full
layers of cathode, organic molecules and anode. The anode layer forms a matrix
in thin film transistor (TFT). This array sets pixels on or off to generate an
image. AMOLEDs consumes less power than PMOLEDs because the TFT array requires
less power than external circuitry, so they are efficient for large displays.
Large screen TVs, monitors and billboards are some products that this type is
used (Burroughes, et al. 1990).
have only substrate, cathode and anode that are transparent components and when
a transparent display is turned on it allows light to pass in both direction
and when a transparent display is turned off are up to 85 percent as
transparent as their substrate. This type of OLED can be either active or
They have opaque
or reflective substrate. They have mainly used for active-matrix design. This
type is used in smart cards.
flexible metallic foils or plastics are used as substrate for foldable OLEDs.
They are very light and strong. Foldable OLEDs are used in cell phones. This
reduces the breakage issue.
In this type, white
light is emitted and produce white light. It is more energy efficient than
regular fluorescent lights that are currently used in homes and buildings.
Their use could potentially reduce energy cost for lighting.
Recent trends in
Fabrication and design technologies
The development of organic printed electronics has
been growing exponentially with a variety of applications and is expected to
bring new things to our future lives. In line with this practice, high
efficiency of organisms with low production processes and certain factors such
as thin body, low weight, bending and low energy consumption is required.
Biodiversity has been investigated in the construction of this field. Basic
guidelines for material construction and the latest advances in polymer
emitting diodes (OLEDs) and organic photovoltaic cells (OPVs) have been
Polymer OLEDs, as well as small OLED molecules, have
(a) a very high resolution from an independent device
(b) Wide viewing
(e) High speed
(f) Low power
notable feature of polymer OLEDs is the use of cost-effectiveness in mass
production. As shown in Table 2, small standard OLEDs, consisting of complex
structures (multilayer structure), are named in the process of mechanical
evaporation. On the other hand, polymer OLEDs have a simple device design,
which can be done with a printer like an inkjet printer.
OLED v/s LCD
LCDs are used in
calculator screen, mobile display, computers and a lot more applications.
Unlike LCDs, OLED produce their own light where LCDs require a backlight. LCDs
has a great amount of power consumption where OLED has low power consumption.
We can see the display in OLED from different angles (up to 160 degree) but in
LCD we cannot see the display in wider way. OLED is slimmer than LCD.(Goyal and Goyal 2019).
display can be lighter and thinner than LED display. With OLED the colours do
not get washed out when you watch from different angles. OLED screens are more energy
efficient when compared to their LED counterparts (Ijeaku, et al. 2015).
· COST: OLED can be
printed onto any fitting substrate by an inkjet printer or even by screen
printing, theoretically making them cheaper to produce than LCD or plasma
· WEIGHT AND
SUBSTRATE: OLED is light weighted and can be created on plastic substrate, the
possibility of flexible light emitting diodes being fabricated or new
applications such as roll up displays embedded in clothing.
EFFECTIVENESS AND THICKNESS: OLEDs are thinner than LED, LCD or plasma displays
and OLED does not create light.
· REACTION TIME:
OLEDs can faster response time than slandered LCD screens.
· OLEDs have wider
viewing angles compared to LCDs
· LIFETIME: Lifetime
of an OLED is lesser than LCD. Red and Green OLED films have longer lifetime
(46,000 to 2,30,000 hours), Blue OLEDs currently have much shorter lifetimes
(up to around 14,000 hours).
· WATER HURT: Water
can easily hurt OLEDs.
CONSUPTION: OLED will consume around 40
percent of the power of an LCD displaying an image.
· OUTSIDE EXECUTION:
As an emissive display technology, OLEDs 100 percent converting electricity to
light, unlike most LCDs which are to some extent reflective.
currently being used in small screens devices such as cell phones, DVD players,
digital camera etc. It can be foldable and flexible and this makes it weight
and space saving technology. Research and development in the field of OLEDs is
proceeding rapidly and may lead to future applications in heads up displays,
automobile, dashboards, billboard type display, home and office lighting and
flexible displays. Video images could be much more realistic and constantly
updated. The future newspaper might be an OLED display that updated with
breaking news and like a normal newspaper you could fold it up when you are
done reading it.
OLED technology is
getting advanced in recent years, their higher efficiency and lower weight will
make them different from other display technology. If we talk about the
performance, the performance of OLEDs meets many of the targets necessary for
applications in display. The most attractive feature of an OLED is it can be
foldable and transparent. We can fold the screen and carry with us anywhere.
Because of foldable we can use it in different ways like foldable newspaper so
that we save papers. We can use OLED in automotive dashboards, billboards types
display, home and office lighting etc.
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