Quantum Dot Display: Quantum Dots (QD), semiconductor nanocrystals that can create pure monochromatic red, green, and blue light, are used in quantum dot displays.
LCD backlights and/or display color filters contain photo-emissive quantum dot particles. Quantum dots are activated by blue light from the display panel to generate pure fundamental colors, which improves display brightness and color gamut by reducing light losses and color crosstalk in color filters.
QD layer film and standard RGB color pigment filters, as well as QD filters with red/green QD color converters and blue passthrough, are used to transmit light. Although the QD color filter technology is most commonly associated with LED-backlit LCDs, it can also be applied to other display technologies that use color filters, such as blue/UV AMOLED/QNED/MicroLED panels.
Photo-emissive quantum dots are most commonly used in LED-backlit LCDs, while blue OLED panels with QD color filters are being investigated.
Quantum dot displays that are electro-emissive or electroluminescent are an experimental type of display that uses quantum-dot light-emitting diodes (QD-LED; also EL-QLED, ELQD, QDEL). Light would be produced directly in each pixel by applying electric current to inorganic nanoparticles, comparable to active-matrix organic light-emitting diode (AMOLED) and MicroLED displays.
- QD-LED displays, according to manufacturers, can accommodate big, flexible displays and do not degrade as quickly as OLEDs, making them ideal for flat-panel TV screens, digital cameras, mobile phones, and handheld games consoles.
- Quantum dots will be used as photo-emissive particles in all commercial items by 2022, including LCD TVs labeled as QLED; electro-emissive QD-LED TVs will only be available in laboratories.
- Wider color gamuts are possible with quantum dot displays, with some devices reaching full coverage of the BT.2020 color gamut.
- Unlike LED-backlit LCDs, QD-OLED and QD-LED displays can attain the same contrast as OLED/MicroLED displays with “perfect” black levels in the off state.
In the 1990s, the concept of employing quantum dots as a light source was proposed. Imaging with QD infrared photodetectors, light-emitting diodes, and single-color light-emitting devices was among the first uses. Scientists began to recognize the possibilities of creating quantum dots for light sources and displays in the early 2000s.
QDs can be used in novel emissive display architectures because they are photo-emissive (photoluminescent) or electro-emissive (electroluminescent).
When color filtered, quantum dots create monochromatic light, making them more efficient than white light sources and allowing for more rich colors that reach nearly 100% of the Rec. 2020 color range.
Quantum Dot Optical Characteristics
The size and/or composition of QD structures determine their performance. A quantum dot structure, unlike ordinary atomic structures, has the uncommon trait of having energy levels that are substantially dependent on the structure’s size. CdSe quantum dot light emission, for example, can be adjusted from red (5 nm diameter) to violet (1.5 nm dot).
The quantum confinement effect, which is directly related to their energy levels, is the physical cause of QD color. The bandgap energy, which affects the fluorescent light’s energy (and thus hue), is inversely related to the square of the quantum dot’s size.
Larger QDs have more closely spaced energy levels, allowing them to emit (or absorb) lower-energy photons (redder color). To put it another way, as the dot size shrinks, the emitted photon energy increases because more energy is required to limit the semiconductor excitation to a smaller volume.
Because cadmium is not exempt from the European Commission’s RoHS directive for use in lighting, and because of cadmium’s toxicity, newer quantum dot structures use indium instead.
Pure and saturated emission colors with limited bandwidth are characteristic of QD-LEDs, having FWHM (full width at half maximum) in the 20–40 nm range.
The size of the quantum dots may readily be changed to change the emission wavelength. Furthermore, QD-LEDs combine great color purity and endurance with comparable organic light-emitting devices’ efficiency, versatility, and low manufacturing costs.
The visible wavelength range of the QD-LED structure can be varied from 460 nm (blue) to 650 nm (red) (the human eye can detect light from 380 to 750 nm). By modifying the chemical composition of the QDs and device structure, the emission wavelengths have been constantly extended to the UV and NIR ranges.
Quantum Dot Display Comparison
The main distinction is that OLEDs have superior black levels, but quantum dot displays have more colour purity. In fact, the latest quantum dot displays can reproduce up to 93 percent of the visible hues found in nature, whereas OLEDs can only reproduce up to 75 percent of the Rec.
Nanocrystal displays could provide a 30 percent boost in visible spectrum while using 30 to 50 percent less power than LCDs, thanks to the fact that they don’t require illumination. QD LEDs emit 40,000 nits (cd/m2), which is 50–100 times brighter than CRT and LC screens.
Because QDs can be dispersed in both aqueous and non-aqueous solvents, they can be used to create printable and flexible displays of all sizes, including large-screen televisions. QDs can be inorganic, which means they have a longer lifespan than OLEDs (however, since many parts of QD-LED are often made of organic materials, further development is required to improve the functional lifetime.)
Pick-and-place microLED displays are emerging as a competitor to nanocrystal displays, in addition to OLED displays. Samsung has devised a method for producing 1 million-hour-long self-emissive quantum dot diodes.
Other benefits include more intense green colors, polymer manufacturability, thinner displays, and the ability to synthesize several colors with the same material.
Because blue quantum dots are just slightly larger than the minimum size, they necessitate extremely precise timing control during the reaction. To attain pure white, a display must provide about equal luminosities of red, green, and blue across the whole spectrum, as described by CIE Standard Illuminant D65.
However, in comparison to green and red, the blue component of the display may have inferior color purity and/or precision (dynamic range), because the human eye is three to five times less sensitive to blue under daylight situations, according to the CIE luminosity function.