WORKING OF OLED DISPLAY
PROJECT IN PHYSICS
Submitted by:
Hussain Abdul Kadhir
Class XII Science
Submitted to:
Mr. NIKHIL V JONES
SUBMITTED AS A PARTIAL FULFILMENT OF THE
SUBJECT PHYSICS AS REQUIRED FOR ALL INDIA
SENIOR SECONDARY CERTIFICATE EXAMINATION
(AISSCE)
MARCH 2022-23
BHAVAN’S PUBLIC SCHOOL, DOHA, QATAR
CERTIFICATE
Certificate to bonafide record of the project work titled WORKING OF OLED
DISPLAY in PHYSICS, done by Hussain Abdul Kadhir of class XII SCIENCE
in Bhavan’s Public School, Doha, Qatar, during the Academic Year 2022-2023.
Register Number……………………
Principal …………………… Teacher in Charge: NIKHIL V JONES
Date ……………………
Submitted for All India Senior Secondary School Practical Examination in
PHYSICS, held at Bhavan’s Public School, Doha-Qatar, in 2021 – 2022.
Internal Examiner External Examiner
Name ……………………………… Signature …………………………
Name ……………………………… Signature …………………………
ACKNOWLEDGEMENT
I would like to extend my deepest appreciation and thanks to
all those for guiding and helping me to complete this project.
With immense sense of gratitude I wish to acknowledge
and thank our respected Principal, Mr.M.P.PHILIP, for his
incessant encouragement, constant support and invaluable
guidance and the ample facilities rendered to me, where I was
able to gather a lot information about my topic, which helped
me in improving my knowledge and idea about my project.
My profound thanks is to my mentor and guide
Mrs.NIKHIL V JONES for endowing this opportunity and
whose contribution in stimulating suggestion and
encouragement helped me to coordinate my project. This
research project wouldn’t have been possible without the
timely assistance of my teachers and parents.
My sincere gratitude to each and every one of them.
CONTENT
Basic concepts to understand working of OLED 5
Electroluminescence 5
Diodes 5
Light Emitting Diodes 6
Pixels in a Display 7
Display technologies 7
LCD 7
LED 8
Twisted nematic (TN) 8
In-plane switching (IPS) 8
What is OLED? 9
History 9
Advantages OLED display 9
Architecture of OLED 10
Working Principle 12
Types of OLED 12
Passive-matrix OLED (PMOLED) 12
Active-matrix OLED (AMOLED) 13
Commercialization of Polymer OLEDs 14
Bibliography 15
Basic concepts to understand working of OLED
Electroluminescence
Electroluminescence involves the conversion of
electrical energy into non-thermal emitted light. It is
the production of light by the flow of electrons, as
within certain crystals. Electroluminescence is one of
the few instances in which a direct conversion of
electric energy into visible light takes place without
the generation of heat.
Diodes
A diode is a semiconductor device that essentially acts as a one-way switch for
current. It allows current to flow easily in one direction, but severely restricts
current from flowing in the opposite direction. When a diode allows current
flow, it is forward-biased. When a diode is reverse-biased, it acts as an
insulator and does not permit current to flow.
A diode is considered a semiconductor device that has two leads and functions
as a one-way door for electric current. Semiconductors can be conductors or
insulators. Their resistance can be controlled by increasing or decreasing its
resistance called doping. Doping is the process of adding impurity atoms to the
material.
There are two types of semiconductor materials:
● N-type material – adding amounts of arsenic, phosphorous, antimony,
bismuth and other pentavalent elements can produce an N-type
semiconducting material. It has extra electrons. Its extra negatively
charged particles move from a negatively charged area to a positively
charged area.
● P-type material – adding amounts of aluminium, gallium, boron, indium
and others can produce a P-type semiconducting material. It has extra
holes.
Having holes means the absence of an electron and having a positive charge.
Every time an electron moves into a hole, it creates another hole behind it since
they move in the opposite direction of electrons. Combining the N-type and
P-type material forms a P-N junction. You can see the depletion region on
either side of the diode junction. This region is depleted of free electrons and
holes. Electrons from the N-type side fill the holes on the P-type side
Light Emitting Diodes
Light-emitting diodes are heavily doped p-n junctions. Based on the
semiconductor material used and the amount of doping, an LED will emit a
coloured light at a particular spectral wavelength when forward biased.
Pixels in a Display
A pixel is defined as a picture element. Each pixel contains red, green, and blue
colour information (referred to as subpixels). By changing the values of sub
pixels we can make any colour. At a reasonable viewing distance, individual
pixels are (usually) invisible to our eyes.
Display technologies
Screens dominate our lives, and we’re looking at them more and more. Between
the screens on phones, TVs, computers, and even fridges, we rely on looking at
a screen for many aspects of your life. But those displays can actually be made
in a number of different ways. And different display types offer different
advantages and disadvantages.
LCD
LCDs, or liquid crystal displays, are the oldest of all display types on this list.
They are made up of two primary components: a backlight and a liquid crystal
layer. Liquid crystals are tiny rod-shaped molecules that change their
orientation in the presence of an electric current. In a display, we manipulate
this property to allow or block light from passing through.
Since liquid crystals don’t produce any light by themselves, LCDs rely on a
white (or sometimes blue) backlight. The liquid crystal layer then simply has to
let this light pass through, depending on the image that needs to be displayed.
LED
These so-called LED displays still use a liquid crystal layer. The only difference
is that the backlights used to illuminate the display now use LEDs instead of
cathode fluorescent lamps, or CFLs. LEDs are a better light source than CFLs in
almost every way. They are smaller, consume lesser power, and last longer.
However, the displays are still fundamentally LCDs.
Twisted nematic (TN)
TN displays have liquid crystals laid out in a twisted, helical structure. Their
default “off” state allows light to pass through two polarising filters. However,
when a voltage is applied, they untwist themselves to block light from passing
through.
TN panels have been around for decades in devices like handheld calculators
and digital watches. In these applications, you only need to power sections of
the display where you don’t want light. In other words, it is an incredibly
energy-efficient technology. Twisted nematic panels are also cheap to
manufacture.
In-plane switching (IPS)
Instead of a twisted orientation, liquid crystals in an IPS display are oriented
parallel to the panel. In this default state, light is blocked — the exact opposite
of what happens in a TN display. Then, when a voltage is applied, the crystals
simply rotate in the same plane and let light through
What is OLED?
OLED (Organic Light Emitting Diodes) is a flat light emitting technology, made
by placing a series of organic thin films between two conductors. When
electrical current is applied, a bright light
is emitted.
History
Organic semiconductors were discovered
in the mid-1970s by Alan Heeger, Alan
MacDiarmid, and Hideki Shirakawa,
who shared the Nobel Prize in Chemistry
in 2000 for their work.
The first efficient OLED—described as "a
novel electroluminescent device...
constructed using organic materials as the
emitting elements"—was developed by
Ching Tang and Steven VanSlyke, then working in the research labs at
Eastman Kodak, in 1987. Their work, though novel, built on earlier research
into electroluminescence, which was first reported in organic molecules by a
French physicist named André Bernanose in the 1950s. He and his colleagues
applied high-voltage AC (alternating current) electric fields to thin films of
cellulose and cellophane "doped" with acridine orange (a fluorescent, organic
dye).
By 1970, Digby Williams and Martin Schadt had managed to create what
they called "a simple organic electroluminescent diode" using anthracene, but it
wasn't until Tang and VanSlyke's work, in the 1980s, that OLED technology
became truly practical.
Milestones in the development of OLEDs since then have included the first
commercial OLED (Pioneer, 1997), the first full-sized OLED display (Sony,
2001), the first OLED mobile phone display (Samsung, 2007), commercial
OLED lighting systems (Lumiotec, 2013), and large-screen commercial OLED
TVs (by Samsung, LG, Panasonic, Sony, and others in 2012 and 2013)
Advantages OLED display
Lambertian emitters
OLED pixels are Lambertian emitters—the displays that appear equally bright
from viewing angles up to 170 degrees. This compares with the narrower
viewing angles of liquid crystal display (LCD) technology whereby the
brightness of the light source typically falls by half outside of a 90–100 degrees
viewing angle (although some disingenuous TV manufacturers claim
differently).
Power consumption
An OLED display does not rely on backlight to illuminate the screen. It emits
visible light in low ambient light conditions without compromising the contrast
ratio; hence, it eliminates the backlight, which reduces the power consumption
typically by up to 60%–80% as compared to devices that rely on backlighting.
Response time
Theoretically, OLEDs are capable of rapidly changing their response times for
leading consumer TVs that respond in 0.01 ms and can refresh a screen at 200
Hz or 100 kHz. LCDs are cited in the 4–8 ms range.
Thinner and lighter displays
OLED technology provides thinner, flexible, and lighter displays because of the
elimination of backlight, and because of their relatively simple construction.
Wide viewing angle
OLEDs offer drastic viewing angles—up to 84 degrees with no luminance
degradation.
Architecture of OLED
The main component in an OLED display is the OLED emitter - an organic
(carbon-based) material that emits light when electricity is applied. The basic
structure of an OLED is an emissive layer sandwiched between a cathode
(which injects electrons) and an anode (which removes electrons).
Modern OLED devices use many more layers in order to make them more
efficient and durable, but the basic functionality remains the same.
OLEDs work in a similar way to conventional diodes and LEDs, but instead of
using layers of n-type and p-type semiconductors, they use organic molecules to
produce their electrons and holes.
A simple OLED is made up of six different layers. On the top and bottom there
are layers of protective glass or plastic. The top layer is called the seal and the
bottom layer the substrate.
In between those layers, there's a negative terminal (sometimes called the
cathode) and a positive terminal (called the anode).
Finally, in between the anode and cathode are two layers made from organic
molecules called the emissive layer (where the light is produced, which is next
to the cathode) and the conductive layer (next to the anode).
Working Principle
● To make an OLED light up, we simply attach a voltage (potential
difference) across the anode and cathode.
● As the electricity starts to flow, the cathode receives electrons from the
power source and the anode loses them (or it "receives holes”).
● Now we have a situation where the added electrons are making the
emissive layer negatively charged (similar to the n-type layer in a
junction diode), while the conductive layer is becoming positively
charged (similar to p-type material).
● Positive holes are much more mobile than negative electrons so they
jump across the boundary from the conductive layer to the emissive layer.
When a hole (a lack of electron) meets an electron, the two things cancel
out and release a brief burst of energy in the form of a particle of light—a
photon, in other words. This process is called recombination, and because
it's happening many times a second the OLED produces continuous light
for as long as the current keeps flowing.
We can make an OLED produce colored light by adding a colored filter into our
plastic sandwich just beneath the glass or plastic top or bottom layer. If we put
thousands of red, green, and blue OLEDs next to one another and switch them
on and off independently, they work like the pixels in a conventional LCD
screen, so we can produce complex, hi-resolution colored pictures.
Types of OLED
Passive-matrix OLED (PMOLED)
PMOLEDs have strips of cathode, organic layers
and strips of anode. The anode strips are arranged
perpendicular to the cathode strips. The
intersections of the cathode and anode make up the
pixels where light is emitted. External circuitry
applies current to selected strips of anode and
cathode, determining which pixels get turned on
and which pixels remain off. The brightness of
each pixel is proportional to the amount of applied
current.
Active-matrix OLED (AMOLED)
AMOLEDs have full layers of cathode, organic
molecules and anode, but the anode layer overlays a
thin film transistor (TFT) array that forms a matrix.
The TFT array itself is the circuitry that determines which pixels get turned on
to form an image.
Commercialization of Polymer OLEDs
Future OLED Applications
Research and development in the field of OLEDs is proceeding rapidly and may
lead to future applications in heads-up displays, automotive dashboards,
billboard-type displays, home and office lighting and flexible displays. Because
OLEDs refresh faster than LCDs -- almost 1,000 times faster -- a device with an
OLED display could change information almost in real time. The newspaper of
the future might be an OLED display that refreshes with breaking news and like
a regular newspaper, you could fold it up when you're done reading it and stick
it in your backpack or briefcase.In the near future, we can expect many devices
and applications of flexible and transparent OLEDs such as:
● Transparent displays embedded in windows
● Displays that can be worn
● Vehicles will have useful, transparent information visible to its occupants
● Vehicle exteriors will utilise a thin OLED lighting film
● Timely and relevant information streamed from the internet will be
displayed in your line-of-sight
● Military can be aided with this technology through goggles, visors, or
contact lenses
Bibliography
https://www.explainthatstuff.com/how-oleds-and-leps-work.html
https://bgr.com/guides/display-types-explained/
https://www.oled-info.com/oled-technology
https://www.fluke.com/en-us/learn/blog/electrical/what-is-a-diode
