Quantum dot display
[1][2][3] LED-backlit LCDs are the main application of photo-emissive quantum dots, though blue organic light-emitting diode (OLED) panels with QD color filters are now coming to market.
A widespread practical application is using quantum dot enhancement film (QDEF) layer to improve the LED backlighting in LCD TVs.
[24][26][27] Because quantum dots depolarize the light, output polarizer (the analyzer) needs to be moved behind the color converter and embedded in-cell of the LCD glass; this would improve viewing angles as well.
In-cell arrangement of the analyzer and/or the polarizer would also reduce depolarization effects in the LC layer, increasing contrast ratio.
As only blue or UV light passes through the liquid crystal layer, it can be made thinner, resulting in faster pixel response times.
[26][28] Nanosys made presentations of their photo-emissive color converter technology during 2017; commercial products were expected by 2019, though in-cell polarizer remained a major challenge.
[29][20][30][31][32][33][34][35][36] As of December 2019, issues with in-cell polarizer remain unresolved and no LCDs with QD color converter appeared on the market since then.
Nanorods have a larger emitting surface compared to planar LED, allowing increased efficiency and higher light emission.
This technology has also been called true QLED display,[63] and Electroluminescent quantum dots (ELQD, QDLE, QDEL, EL-QLED).
[11][12][10] To realize all-QD LED, the challenge that should be overcome is the currently poor electrical conduction in the emitting QD layers.
[67][68] As cadmium-based materials cannot be used in lighting applications due to their environmental impact,[69] InP (indium phosphide) ink-jet solutions are being researched by Nanosys, Nanoco, Nanophotonica, OSRAM OLED, Fraunhofer IAP, Merck, and Seoul National University, among others.
[72] Mass production of active-matrix QLED displays using ink-jet printing was expected to begin in 2020–2021,[73][74][75][35][36] but as of 2024, longevity issues are not resolved and the technology remains in prototyping stage.
QD-LEDs are characterized by pure and saturated emission colors with narrow bandwidth, with FWHM (full width at half maximum) in the range of 20–40 nm.
Moreover, QD-LED offer high color purity and durability combined with the efficiency, flexibility, and low processing cost of comparable organic light-emitting devices.
The emission wavelengths have been continuously extended to UV and NIR range by tailoring the chemical composition of the QDs and device structure.
During solvent drying, the QDs phase separate from the organic under-layer material (TPD) and rise towards the film's surface.
Since spin-casting does not allow lateral patterning of different sized QDs (RGB), phase separation cannot create a multi-color QD-LED.
The contact printing process for forming QD thin films is a solvent-free water-based suspension method, which is simple and cost efficient with high throughput.
Since charge transport layers in QD-LED structures are solvent-sensitive organic thin films, avoiding solvent during the process is a major benefit.
A QD-LED was fabricated with an emissive layer consisting of 25-μm wide stripes of red, green and blue QD monolayers.
QDs are dispersable in both aqueous and non-aqueous solvents, which provides for printable and flexible displays of all sizes, including large area TVs.
