What’s the difference between LCD and OLED displays?

1
Whats the difference between LCD and OLED
displays?

• By Mehmet Tugrul, Field Applications
  Engineer for OSD Displays (an OLED panel supplier
  and division of New Vision Display)

2
Display Technologies
3

• There are two main competing display technologies
  in the market today LCD and OLED. The mature and
  dominant technology is the Liquid Crystal
  Display (LCD), while the up-and-coming challenger
  is the Organic Light Emitting Diode Display (OLED
  display). The main difference between LCD and
  OLED displays is how they create the light and
  the colors of the image being displayed. This
  leads to application dependent strengths and
  weaknesses of either technology.
• OLEDs operate via a solid-state technology, where
  the individual pixels can emit light in various
  colors and intensity without the need for an
  additional light source or color filter. The
  light-emitting portion of an OLED display is
  comprised of multiple layers of very specific
  organic semiconductor materials which can be
  adjusted to emit light in specific wavelengths.
  These organic layers have a typical thickness in
  the order of 100nm. In addition, no backlight is
  required, allowing for a very thin display
  module.

4
Layers of an OLED cell
The organic layers beginning on the cathode side
of the device consist of several electron
transport layers, a recombination layer and end
with a hole transport layer on the anode side.
The electron transport layers in the OLED
stack-up allow movement of electrons from the
cathode toward holes supplied from the anode. The
electrons and holes recombine in the emissive
recombination layer of the film stack-up. 
5

• This recombination relaxes the energy levels of
  the electrons, which produces an emission of
  light. The wavelength of the emitted light is
  dependent on the chemical composition of the
  organic materials used in the recombination
  layer. The intensity of the light is controlled
  by the amount of current flowing through the
  OLEDs organic layers. In OLEDs, the individual
  pixels can emit red, green, or blue light, or
  alternatively they emit white light, which must
  then pass through color filters.
• In LCD display technology, the individual pixels
  modulate light. An applied voltage changes the
  orientation of liquid crystal molecules that in
  conjunction with a pair of polarizers function
  as a light shutter by either blocking or allowing
  light to pass through. LCD displays, therefore,
  require an additional light source, either from
  reflected ambient light or more commonly from a
  backlight (an array of LEDs arranged behind or
  next to the LCD panel). LCD color can be created
  by either switching the backlight quickly between
  red, green and blue, or more commonly by
  adding color filters to the individual pixels.
  Because OLED displays dont require the
  additional backlight, polarizers, or color filter
  components of an LCD module, they can be made
  much thinner than LCD displays of equivalent size
  and resolution.

6
LCD Example
7

• OLED display technology can offer power-saving
  advantages over LCDs, which is important,
  especially for battery-powered applications such
  as mobile phones. An OLEDs power consumption
  will vary with image content and brightness, as
  light is generated only at the individual pixels
  needed to display the image. A dark image or a
  graphic on a black background will consume much
  less power than bright images or graphics. In
  contrast, LCD backlights must be ON while the
  display operates. Its possible to control
  individual zones of the backlight separately to
  save power, but this added complexity is usually
  only applied in larger displays.
• OLEDs can achieve a much higher contrast ratio if
  reflections from the front surface are carefully
  controlled. If no current flows through an OLED
  pixel, it does not emit any light. In contrast
  the shutter effect of an LCD pixel does not block
  100 of the light. Depending on the specific LCD
  technology used and the angle of observation, a
  small percentage of the light generated in the
  backlight can escape. This can wash out dark
  areas of an image. It is possible but expensive
  to limit this light leakage to a point where the
  contrast of an OLED and LCD display become
  perceptually equivalent.

8

• RGB OLEDs naturally generate a narrow bandwidth
  of light. This leads to very saturated primary
  colors and a wide color gamut. This enables OLED
  technology to display colors which are not easily
  accessible to LCDs unless RGB backlights or
  quantum dot phosphors are used for the
  illumination. Often OLED colors are used as is,
  however, for very high image color fidelity, such
  high color saturation needs to be electronically
  tuned down, to match the color bandwidth of the
  rendering chain.
• LCDs offer an advantage over OLEDs in
  applications where a continuous static image is
  required. The light emitting materials (also
  called phosphors) in OLEDs are affected by
  luminance decay as a function of the total amount
  of current that has passed through the pixel.
  This decay differs for red, green and blue
  phosphors. The dimming effect is subtle, but when
  adjacent pixels are illuminated at the same time
  it can become noticeable as an undesired
  brightness variation or color shift. LCDs dont
  suffer from this dimming effect, which makes them
  a more suitable solution for applications with
  static images or images with static elements.

9
LCDs are still preferred technology for laptop
applications due to lower cost trade-off
10

• Another advantage of LCD technology is the wide
  variety of different variations to choose from.
  Depending on the application certain trade-offs
  can be very attractive. An example is much lower
  cost for a laptop display compared to a tablet.
  This is achieved by allowing poor image
  performance when viewed from the direction the is
  usually blocked by the keyboard. In a tablet
  where good viewing performance is required from
  any direction, much higher cost LCDs or OLEDs
  must be used.
• OLEDs offer an excellent solution for a variety
  of applications Glucometers and thermometers,
  fitness trackers, professional audio equipment,
  Wi-Fi hotspots, radar detectors, dive computers,
  biometric transaction devices, and military
  communications equipment.

11
Fitness watches often use OLED displays
They can be used to replace old TN LCDs or add
dynamic push buttons on industrial equipment.
They can be customized to various resolutions,
FPC configurations, colors and shapes (e.g.
octagonal, round, etc.) and can even be made into
flexible and transparent displays offering OLED
display panel suppliers some exciting
capabilities for their customers things that
were previously impossible with LCDs.
12

• New Vision Display and OSD Displays (a Division
  of New Vision Display specializing in OLED
  displays) are happy to discuss each technologys
  strengths and weaknesses, and provide product
  designers with expert guidance on choosing the
  right display module solution for their
  design. Contact us today to learn more!

13
Source

• http//newvisiondisplay.com/difference-lcds-oled-d
  isplays/

14
Thank You