2. What is an OLED?
OLED - Organic Light Emitting Diode
An OLED is any light emitting diode (LED) which emissive
electroluminescent layer is composed of a film of organic
compounds.
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.
3. History of OLEDs
• First developed in the early 1950s in France
• Early technology would emmite a short burst of light when a
voltage was applied
• This early form applied high-voltage alternating current field to
crystalline thin films of acridine orange and quinacrine.
• 1960s - AC-driven electroluminescent cells
using doped anthracene was developed
• In a 1977 paper, Shirakawa et al. Reported
high conductivity in similarly oxidized and
iodine-doped polyacetylene.
• In 1987 Chin Tang and Van Slyke
introduced the first light emitting diodes
from thin organic layers.
• In 1990 electroluminescence in polymers
was discovered.
4. Architecture of OLEDs
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.
Organic layer:
o Conducting layer - This layer is made of
organic plastic molecules that transport
"holes" from the anode. One conducting
polymer used in OLEDs is polyaniline.
o 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 is made. One polymer used in the
emissive layer is polyfluorene.
Cathode (may or may not be transparent depending on the type of OLED) -
The cathode injects electrons when a current flows through the device.
5. Working of OLEDS:
• 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. These materials have conductivity levels ranging
from insulators to conductors, and therefore are considered
organic semiconductors. The highest occupied and lowest
unoccupied molecular orbitals (HOMO and LUMO) of
organic semiconductors are analogous to the valence and
conduction bands of inorganic semiconductors.
6. • During operation, a voltage is applied across the OLED
such that the anode is positive with respect to the cathode.
Anodes are picked based upon the fact of how good their
optical transparency, electrical conductivity, and chemical
stability are. 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. This
happens closer to the emissive layer, because in organic
semiconductors holes are generally 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.
7. • As electrons and holes are fermions with half integer spin,
an exciton may either be in a singlet state or a triplet state
depending on how the spins of the electron and hole have
been combined. Statistically three triplet excitons will be
formed for each singlet exciton. Decay from triplet states
(phosphorescence) is spin forbidden, increasing the
timescale of the transition and limiting the internal efficiency
of fluorescent devices. Phosphorescent organic light-
emitting diodes make use of spin–orbit interactions to
facilitate intersystem crossing between singlet and triplet
states, thus obtaining emission from both singlet and triplet
states and improving the internal efficiency
8. Types of OLEDs
Passive OLEDs
• The organic layer is between
strips of cathode and anode that
run perpendicular
• The intersections form the pixels
• Easy to make
• Use more power
• Best for small screens
Active OLEDs
• Full layers of cathode and
anode
• Anode over lays a thin film
transistor (TFT)
• Requires less power
• Higher refresh rates
• Suitable for large screens
9. Current Research for OLEDs
• Manufacturers focusing on finding a
cheap way to produce
o "Roll-to-Roll" Manufacturing
• Increasing efficiency of blue luminance
• Boosting overall lifespan
12. OLED Televisions
• Released XEL-1 in February 2009.
• First OLED TV sold in stores.
• 11'' screen, 3mm thin
• $2,500 MSRP
• Weighs approximately 1.9 kg
• Wide 178 degree viewing angle
• 1,000,000:1 Contrast ratio
Sony
13. Optimus Maximus Keyboard
• Small OLED screen on every key
• 113 OLED screens total
• Each key can be programmed to
preform a series of functions
• Keys can be linked to applications
• Display notes, numerals, special
symbols, HTML codes, etc...
• SD card slot for storing settings
14. Advantages of OLEDs
• Much faster response time
• Consume significantly less energy
• Able to display "True Black" picture
• Wider viewing angles
• Thinner display
• Better contrast ratio
• Safer for the environment
• Has potential to be mass produced inexpensively
• OLEDs refresh almost 1,000 times faster then LCDs
OLED Displays Vs. LCD and Plasma
OLED Lighting Vs. Incandescent and Fluorescent
• Cheaper way to create flexible lighting
• Requires less power
• Better quality of light (ie. no "Cold Light")
• New design concepts for interior lighting
15. Disadvantages of OLEDs
OLED Displays Vs. LCD and Plasma
• Cost to manufacture is high
• Overall luminance degradation
• Constraints with lifespan
• Easily damaged by water
• Limited market availability
OLED Lighting Vs. Incandescent and Fluorescent
• Not as easy as changing a light bulb
16. Future Uses for OLED
Lighting
• Flexible / bendable lighting
• Wallpaper lighting defining new ways to light a space
• Transparent lighting doubles as a window
Cell Phones
• Nokia 888
17. Future Uses for OLED
Transparent Car Navigation System on Windshield
• Using Samsungs' transparent OLED technology
• Heads up display
• GPS system
Scroll Laptop
• Nokia concept OLED Laptop
