What’s the difference between LCD and OLED displays?
By Mehmet Tugrul, Field Applications Engineer (Europe) at New Vision Display
LCD displays have been the go-to display technology for decades, but now we’re seeing more and more OLED displays hit the market. For example, many of the most common smartphones – like the Samsung Galaxy line-up – use OLED displays. So, what is the difference? And why might one technology be better than the other?
OLED Display Technology
The primary difference between LCD and OLED displays is the way in which they’re illuminated. The pixels within OLEDs are self-illuminating, while LCD pixels are not: The entire LCD display must be illuminated by another mechanism such as a backlight.
Organic Light Emitting Devices (OLEDs) can generally be grouped into two categories based on their molecular structure: Monomers and polymers. Small molecule organic LEDs or SMOLEDs have monomers, which can be the building blocks of polymers. Polymer Large Molecule or Polymer type OLED (PLED). This thick-film technology was mostly developed at the University of Cambridge which spawned Cambridge Display Technologies (CDT).
The major differences between SMOLEDs and PLEDs are the manufacturing processes. The basic small molecule OLED pixel structure consists of a stack of thin organic layers between a transparent anode and a metallic cathode. The organic layers are comprised of a hole-injection layer, a hole-transport layer, an emissive layer, and an electron-transport layer. When a voltage is applied to the OLED, the holes (positive electric charge) and the electrons (negative electric charge) are generated from each of the two electrodes. When these holes and electrodes recombine in the emissive layer, the organic materials move into a high energy state called “excitation”. The excess energy in the material is released as light as the emissive layer returns to its original stable state, or “ground state”. The emitted color is determined by the doping of the material used in the emitting layer.
Advantages of OLED Displays
LCDs and OLEDs have a number of differences. One of the advantages of OLEDs is that they are self-illuminating and therefore don’t require a backlight mechanism. This means they can be made into much thinner forms than LCDs. They’re also uniformly bright, offer wide viewing angles (~90 degrees) with no gray inversion, and have better contrast than LCDs, offering – in some situations – a better quality image than LCDs. Their switching time is much shorter than that of LCDs as well, making them a better solution for video playback equipment. OLEDs are solid-state devices and have a wide operating temperature range. They will operate properly even at sub-zero temperatures, which isn’t possible for LCDs unless special heading mechanisms are built into them.
Disadvantages of OLED Displays
OLEDs don’t always function as well as LCDs when it comes to power consumption. If the content on the display is rich, it will drain their battery faster than it would on an LCD. Also, OLED emitter materials are sensitive to oxidation and moisture, making them less than ideal for wet environments.
The light intensity increases towards shorter wavelengths faster which can result in color shift errors. An increase in luminance accelerates the loss of intensity and will shorten the product service life. The average life of the RGB colors are not the same. Red and blue lose luminance at a faster rate than green.
Other disadvantages include:
- Passive Matrix OLEDs are limited in resolution and size by the multiplex rate
- The size limit is around 3.0” diagonal
- Resolution is limited to 128 Mux
- Poor direct sunlight readability
- Image sticking, due to differential aging of pixels
Common Applications for OLED Displays
OLEDs are a great solution for many applications. They’re commonly found in glucometers and thermometers, fitness trackers, professional audio equipment, WI-FI hotspots, radar detectors, dive computers, biometric transaction devices, and military communications equipment. They can also be used to replace old TN LCDs and as dynamic push buttons on industrial equipment.
OLEDs can be customized to various resolutions, FPC configurations, colors and shapes such as octagonal and round displays. They can also be made into flexible and transparent displays. This gives OLED display panel suppliers, such as New Vision Display and OSD Displays (a Division of New Vision Display) some exciting new display capabilities for their customers – things that were previously impossible with LCDs.
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