QLED vs OLED: Key Differences in Display Technologies

This article compares QLED and OLED technologies, highlighting the key differences between QLED and OLED TVs. It also touches upon the basics of OLED technology, its advantages and disadvantages, and how it works.

OLED: Organic Light Emitting Diode

• An OLED is an electronic device composed of a series of organic thin films placed between two conductors.
• It operates on the principle of electro-luminescence, where bright light is emitted when an electrical current is applied.
• The structure of an OLED typically consists of a Cathode, Emissive Layer, Conductive Layer, Anode, and a Substrate.
• When a voltage is applied, current flows from the cathode to the anode through the organic layers.
• This causes electrons to travel towards the emissive layer and be removed from the conductive layer.
• The removal of electrons from the conductive layer leaves “holes,” which need to be filled with electrons in the emissive layer.
• As a result, these holes jump to the emissive layer and recombine with electrons. As electrons drop into holes, they release their extra energy as light. This is how light emission occurs in an OLED device.

QLED: Quantum-dot Light Emitting Diode

Quantum dots are crucial elements in QLED and IGZO display technologies. Let’s delve into what quantum dots are.

What are Quantum Dots?

• Quantum dots are tiny semiconductor nanocrystals, ranging in size from 2 nm to 10 nm.
• They emit colors based on their size and the energy gap of the materials used. Larger dimensions result in longer emitted wavelengths.
• Figure 2 illustrates the relationship between wavelength and fluorescence.

• Various semiconductor materials are used to create quantum dots, including CdSe, CdS, PbSe, PbS, InAs, and InP.
• Nowadays, cadmium-free technologies are favored because they generate numerous color combinations, leading to better light efficiency.

• In QLED construction, a thin layer of quantum dots is used in front of the backlight.

• As shown in Figure 3, six layers are used to construct the color image: backlight panel, reflector, polarizing filter, TFT array, color filter glass, quantum dots color filter, and polarizing filter.

  • Backlight Panel: Illuminates the LEDs from the side or back of the display panel, using a special light source to produce a visible image that is then passed to the reflector.
  • Reflector: Enhances the uniformity of the illuminance distribution on the target region of the image plane.
  • Polarizing Filter: Changes the settings of the image passed by the reflector to suppress glare or blur. Different polarizers are used in display technology.
  • TFT Array: Matches the size of the quantum dots in the color filter and handles color reproduction, managing the display of pixels on the screen.
  • Color Filters: With blue LEDs, can produce billions of colors with peak brightness and better clarity.
  • Polarizing Filter: Provides the final touch to the display, generating a crystal-clear image on the screen.

• Refer to the advantages and disadvantages of quantum dots used in the construction of QLED displays for more information.

QLED vs OLED: A Tabular Comparison

• OLEDs illuminate their LEDs directly, eliminating the need for a separate light source.
• QLEDs do not produce light independently; instead, they rely on a backlight unit for illumination. This light is then passed to the reflector to ensure uniform illumination on the image plane. Quantum dots are more resistant to moisture, which contributes to a longer lifespan for QLED TVs. Furthermore, this high moisture resistance eliminates the need for an expensive vacuum evaporation process.
• The following table summarizes the key differences between QLED and OLED TVs.

This guide provides a comparison between QLED and OLED technologies and their respective TV types.