Quantum dot display

Source: Wikipedia, the free encyclopedia.
Colloidal quantum dots irradiated with a UV light. Different sized quantum dots emit different color light due to quantum confinement.

A quantum dot display is a

active-matrix organic light-emitting diode (AMOLED) or QNED/MicroLED display panels.[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 being researched.

Electro-emissive or electroluminiscent quantum dot displays are an experimental type of display based on quantum-dot light-emitting diodes (QD-LED; also EL-QLED, ELQD, QDEL). These displays are similar to AMOLED and MicroLED displays, in that light would be produced directly in each pixel by applying electric current to inorganic nano-particles. Manufacturers asserted that QD-LED displays could support large, flexible displays and would not degrade as readily as OLEDs, making them good candidates for

flat-panel TV screens, digital cameras, mobile phones and handheld game consoles.[4][5][6]

As of June 2016,[update] all commercial products, such as LCD TVs branded as QLED, employ quantum dots as photo-emissive particles; electro-emissive QD-LED TVs exist in laboratories only.

BT.2020 color gamut.[9][10][11]
QD-OLED and QD-LED displays can achieve the same contrast as OLED/MicroLED displays with "perfect" black levels in the off state, unlike LED-backlit LCDs.

Working principle

Samsung QLED TV 8K - 75 inches

The idea of using quantum dots as a light source emerged in the 1990s. Early applications included imaging using QD infrared photodetectors,

light emitting diodes and single-color light emitting devices.[12] Starting in the early 2000s, scientists started to realize the potential of developing quantum dots for light sources and displays.[13]

QDs are either photo-emissive (

electroluminescent) allowing them to be readily incorporated into new emissive display architectures.[14] Quantum dots naturally produce monochromatic light, so they are more efficient than white light sources when color filtered and allow more saturated colors that reach nearly 100% of Rec. 2020 color gamut.[10][11][9]

Quantum dot enhancement layer

A widespread practical application is using quantum dot enhancement film (QDEF) layer to improve the

color gamut
.

The first manufacturer shipping TVs of this kind was

TCL to produce and market QD-enhanced TVs.[19][20]

Quantum dot on glass (QDOG) replaces QD film with a thin QD layer coated on top of the light-guide plate (LGP), reducing costs and improving efficiency.[21][22]

Traditional white LED backlights that use blue LEDs with on-chip or on-rail red-green QD structures are being researched, though high operating temperatures negatively affect their lifespan.[23][24]

Quantum dot color converter

QD color converter (QDCC) LED-backlit LCDs would use QD film or ink-printed QD layer with red/green sub-pixel patterned (i.e. aligned to precisely match the red and green subpixels) quantum dots to produce pure red/green light; blue subpixels can be transparent to pass through the pure blue LED backlight, or can be made with blue patterned quantum dots in case of UV-LED backlight. This configuration effectively replaces passive color filters, which incur substantial losses by filtering out 2/3 of passing light, with photo-emissive QD structures, improving power efficiency and/or peak brightness, and enhancing color purity.[23][25][26] 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. To reduce self-excitement of QD film and to improve efficiency, the ambient light can be blocked using traditional color filters, and reflective polarizers can direct light from the QDCC towards the viewer. As only blue or UV light passes through the liquid crystal layer, it can be made thinner, resulting in faster pixel response times.[25][27]

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.[28][19][29][30][31][32][33][34][35] As of December 2019, issues with in-cell polarizer remain unresolved and no LCDs with QD color converter appeared on the market since then.[36]

QD color converters can be used with OLED or micro-LED panels, improving their efficiency and color gamut.[21][35][37][38] QD-OLED panels with blue emitters and red-green color converters are researched by Samsung and TCL; as of May 2019, Samsung intends to start production in 2021.[39][40][41][42][43][44] In October 2019, Samsung Display announced an investment of $10.8 billion in both research and production, with the aim to convert all their 8G panel factories to QD-OLED production during 2019–2025.[45][46][47][48] Samsung Display presented 55" and 65" QD-OLED panels at CES 2022, with TVs from Samsung Electronics and Sony to be released later in 2022.[49] QD-OLED displays show better color volume, covering 90% of Rec.2020 color gamut with peak brightness of 1500 nits, while current OLED and LCD TVs cover 70–75% of Rec.2020 (95–100% of DCI-P3).[50][51][52]

QNED

A further development of QD-OLED displays is quantum dot nanorod emitting diode (QNED) display

GaN blue nanorod LEDs. Nanorods have a larger emitting surface compared to planar LED, allowing increased efficiency and higher light emission. Nanorod solution is ink-printed on the substrate, then subpixels are aligned in-place by electric current, and QD color convertors are placed on top of red/green subpixels.[54][55] Samsung Display was expected to begin test production of QNED panels in 2021,[56]
[53] with mass production in 2024-2025, but test production has been postponed as of May 2022.[57][58]

Starting in 2021 LG Electronics introduced a series of TVs branded as "QNED Mini LED". These TVs are based on LCD displays with mini LED backlighting and don't use self-emissive technologies.[59] LG explains that the acronym "QNED" in their case stands for "Quantum Nano-Emitting Diode".[60] The following year LG launched "QNED" TVs that don't use mini LED technology but still rely on LCD technology.

Self-emissive quantum dot diodes

See also: AMOLED, MicroLED, and LED display

Self-emissive quantum dot displays will use electroluminescent QD

passive matrix array. Rather than requiring a separate LED backlight for illumination and TFT LCD to control the brightness of color primaries, these QDEL displays would natively control the light emitted by individual color subpixels,[61] greatly reducing pixel response times by eliminating the liquid crystal layer. This technology has also been called true QLED display,[62] and Electroluminescent quantum dots (ELQD, QDLE, QDEL, EL-QLED).[63][64]

The structure of a QD-LED is similar to the basic design of an OLED. The major difference is that the light emitting devices are quantum dots, such as

color gamut from QD-LEDs exceeds the performance of both LCD and OLED display technologies.[10][11][9] To realize all-QD LED, the challenge that should be overcome is the currently poor electrical conduction in the emitting QD layers.[66][67]

As cadmium-based materials cannot be used in lighting applications due to their environmental impact,[68] InP (indium phosphide) ink-jet solutions are being researched by Nanosys, Nanoco, Nanophotonica, OSRAM OLED, Fraunhofer IAP, Merck, and Seoul National University, among others.[33][69][70] As of 2019, InP based materials are still not yet ready for commercial production due to limited lifetime.[71]

Mass production of active-matrix QLED displays using ink-jet printing was expected to begin in 2020–2021,[72][73][74][34][35] but as of 2024, longevity issues are not resolved and the technology remains in prototyping stage. Nanosys expects their QD electroluminiscent techology to be available for production by 2026.[75]

At CES 2024, Sharp NEC Display privately demoed prototypes of 12" and 30" display panels.[76][75]

Optical properties of quantum dots

Performance of QDs is determined by the size and/or composition of the QD structures. Unlike simple atomic structures, a quantum dot structure has the unusual property that energy levels are strongly dependent on the structure's size. For example,

bandgap energy that determines the energy (and hence color) of the fluorescent light is inversely proportional to the square of the size of quantum dot. Larger QDs have more energy levels that are more closely spaced, allowing the QD to emit (or absorb) photons of lower energy (redder color). In other words, the emitted photon energy increases as the dot size decreases, because greater energy is required to confine the semiconductor excitation to a smaller volume.[77]

Newer quantum dot structures employ

RoHS directive,[23][78]
and also because of cadmium's toxicity.

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.[13][25] Their emission wavelength is easily tuned by changing the size of the quantum dots. Moreover, QD-LED offer high color purity and durability combined with the efficiency, flexibility, and low processing cost of comparable organic light-emitting devices. QD-LED structure can be tuned over the entire visible wavelength range from 460 nm (blue) to 650 nm (red) (the human eye can detect light from 380 to 750 nm). The emission wavelengths have been continuously extended to UV and NIR range by tailoring the chemical composition of the QDs and device structure.[79][80]

Fabrication process

Quantum dots are solution processable and suitable for wet processing techniques. The two major fabrication techniques for QD-LED are called phase separation and contact-printing.[81]

Phase separation

Phase separation is suitable for forming large-area ordered QD monolayers. A single QD layer is formed by spin casting a mixed solution of QD and an organic semiconductor such as TPD (N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine). This process simultaneously yields QD monolayers self-assembled into hexagonally close-packed arrays and places this monolayer on top of a co-deposited contact. During solvent drying, the QDs phase separate from the organic under-layer material (TPD) and rise towards the film's surface. The resulting QD structure is affected by many parameters: solution concentration, solvent ration, QD size distribution and QD aspect ratio. Also important is QD solution and organic solvent purity.[82]

Although phase separation is relatively simple, it is not suitable for display device applications. Since spin-casting does not allow lateral patterning of different sized QDs (RGB), phase separation cannot create a multi-color QD-LED. Moreover, it is not ideal to have an organic under-layer material for a QD-LED; an organic under-layer must be homogeneous, a constraint which limits the number of applicable device designs.

Contact printing

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. During the process, the device structure is not exposed to solvents. Since charge transport layers in QD-LED structures are solvent-sensitive organic thin films, avoiding solvent during the process is a major benefit. This method can produce RGB patterned electroluminescent structures with 1000 ppi (pixels-per-inch) resolution.[11]

The overall process of contact printing:

  • Polydimethylsiloxane (PDMS) is molded using a silicon master.
  • Top side of resulting PDMS stamp is coated with a thin film of Parylene-c, a chemical-vapor deposited (CVD) aromatic organic polymer.
  • Parylene-c coated stamp is inked via spin-casting of a solution of colloidal QDs suspended in an organic solvent.[contradictory]
  • After the solvent evaporates, the formed QD monolayer is transferred to the substrate by contact printing.

The array of quantum dots is manufactured by self-assembly in a process known as spin casting: a solution of quantum dots in an organic material is poured onto a substrate, which is then set spinning to spread the solution evenly.

Contact printing allows fabrication of multi-color QD-LEDs. A QD-LED was fabricated with an emissive layer consisting of 25-

μm wide stripes of red, green and blue QD monolayers. Contact printing methods also minimize the amount of QD required, reducing costs.[11]

Comparison

Nanocrystal displays would render as much as a 30% increase in the visible spectrum, while using 30 to 50% less power than LCDs, in large part because nanocrystal displays would not need backlighting. QD LEDs are 50–100 times brighter than CRT and LC displays, emitting 40,000 nits (cd/m2). QDs are dispersable in both aqueous and non-aqueous solvents, which provides for printable and flexible displays of all sizes, including large area TVs. QDs can be inorganic, offering the potential for improved lifetimes compared to OLED (however, since many parts of QD-LED are often made of organic materials, further development is required to improve the functional lifetime.) In addition to OLED displays, pick-and-place microLED displays are emerging as competing technologies to nanocrystal displays. Samsung has developed a method for making self-emissive quantum dot diodes with a lifetime of 1 million hours.[83]

Other advantages include better saturated green colors, manufacturability on polymers, thinner display and the use of the same material to generate different colors.

One disadvantage is that blue quantum dots require highly precise timing control during the reaction, because blue quantum dots are just slightly above the minimum size. Since

luminosity function
.

In contrast to traditional LCD panels and Quantum Dot LCD panels, QD-OLEDs suffer from the same screen burn-in effect as normal OLED panels.

See also

Notes

  1. ^ Up to the specified bandwidth, which is in turn a function of the dispersity of the quantum dots.

References

  1. ^ Mu-Hyun, Cho. "Samsung researching quantum dot on MicroLED TVs". ZDNet.
  2. ^ "StackPath". www.laserfocusworld.com. 8 January 2019.
  3. ^ "Quantum Dots to Shrink MicroLED Display Pixels". EETimes. 11 January 2019.
  4. ^ Quantum-dot displays could outshine their rivals, New Scientist, 10 December 2007
  5. ^ "Quantum Dot Electroluminescence". evidenttech.com. Archived from the original on 16 December 2009. Retrieved 3 April 2018.
  6. ^ Bullis, Kevin (1 May 2006). "Nanocrystal Displays". MIT Technology Review. Retrieved 3 April 2018.
  7. ^ www.etnews.com (18 October 2016). "Next Samsung Electronics' QLED TV's Name to Be SUHD QLED TV". etnews.com. Retrieved 3 April 2018.
  8. ^ "How QLED TV could help Samsung finally beat LG's OLEDs". cnet.com. 30 June 2016. Retrieved 3 April 2018.
  9. ^
    doi:10.1002/sdtp.10276. {{cite journal}}: Cite journal requires |journal= (help
    )
  10. ^ a b c Ruidong Zhu, Zhenyue Luo, Haiwei Chen, Yajie Dong, and Shin-Tson Wu. Realizing Rec. 2020 color gamut with quantum dot displays. Optics Express, Vol. 23, No. 18 (2015). DOI:10.1364/OE.23.023680
  11. ^
    PMID 19053797
    .
  12. S2CID 119708221
    .
  13. ^
    PMID 19514711
    .
  14. ^ "Display – Nanoco Technologies". www.nanocotechnologies.com. Archived from the original on 23 March 2014. Retrieved 3 April 2018.
  15. ^ "SONY ANNOUNCES 2013 BRAVIA TVS | Sony". 8 March 2013. Archived from the original on 8 March 2013.
  16. ^ "Full Page Reload". IEEE Spectrum: Technology, Engineering, and Science News. 7 January 2015.
  17. ^ "LG leaps quantum dot rivals with new TV". cnet.com. 16 December 2014. Retrieved 3 April 2018.
  18. ^ "Ultra-slim LCDs and quantum-dots enhanced LEDs enter the market – OLED-Info". www.oled-info.com. Retrieved 3 April 2018.
  19. ^ a b "Samsung, Hisense & TCL form 'QLED Alliance' to take on OLED – FlatpanelsHD". www.flatpanelshd.com. Retrieved 3 April 2018.
  20. ^ "QLED Alliance Kicks Off in Beijing". nanosysinc.com. 18 April 2017. Retrieved 3 April 2018.
  21. ^ a b Hartlove, Jason. "Quantum Dots Moving to the Mainstream" (PDF). Archived from the original (PDF) on 23 December 2017.
  22. ^ "Is QDOG the Future of LCD TV?". Display Supply Chain Consultants. Retrieved 3 April 2018.
  23. ^ a b c "Quantum Dots: Solution for a Wider Color Gamut". samsungdisplay.com. Archived from the original on 20 September 2018. Retrieved 3 April 2018.
  24. ^ Sturgeon, Shane. "HDTV Expert – Three Premium 2017 LCD-TVs Plot Different Paths to Enhanced Performance". hdtvmagazine.com. Archived from the original on 30 June 2018. Retrieved 3 April 2018.
  25. ^ a b c Haiwei Chen, Juan He, and Shin-Tson Wu. Recent advances on quantum-dot-enhanced liquid crystal displays. IEEE Journal of Selected Topics in Quantum Electronics Vol. 23, No. 5 (2017). DOI 10.1109/JSTQE.2017.2649466
  26. ^ Werner, Ken (25 May 2017). "DisplayDaily". www.displaydaily.com. Retrieved 3 April 2018.
  27. ^ H. Chen, G. Tan, M. C. Li, S. L. Lee, and S. T. Wu. Depolarization effect in liquid crystal displays. Optics Express 25 (10), 11315-11328 (2017). DOI 10.1364/OE.25.011315
  28. ^ "Nanosys Quantum Dots at CES 2017 - AVSForum.com". avsforum.com. 12 January 2017. Retrieved 3 April 2018.
  29. ^ "Nanosys Details the Future of Quantum Dots". www.insightmedia.info. 19 June 2017. Retrieved 3 April 2018.
  30. ^ "SID Display Week 2017 – Thank You!". nanosysinc.com. Archived from the original on 20 September 2018. Retrieved 3 April 2018.
  31. ^ "Nanosys Honored for Hyperion Quantum Dot Technology at Display Week". printedelectronicsnow.com. Retrieved 3 April 2018.
  32. ^ Werner, Ken (7 December 2017). "Beginning of the End for the Color Matrix Filter?". www.displaydaily.com. Retrieved 3 April 2018.
  33. ^ a b Palomaki, Peter (5 April 2018). "What's Next for Quantum Dots?". www.displaydaily.com.
  34. ^ a b Dash, Sweta (7 May 2018). "Future of Quantum Dot Display: Niche or Mainstream?". www.displaydaily.com.
  35. ^ a b c "Nanosys Quantum-Dot Update at CES 2018 - AVSForum.com". avsforum.com. 20 January 2018.
  36. ^ "Top Trends in Quantum Dots at SID Display Week 2019 – Part 1". 17 June 2019.
  37. ^ "OLED Materials Report Brings New Insight on QD OLEDs".
  38. ^ "ETNews: SDC is building a QD-OLED TV pilot production line | OLED-Info".
  39. ^ "Samsung: We are developing QD-OLED displays – FlatpanelsHD".
  40. ^ "Samsung Display Accelerating Plans to Shift to QD OLED". November 2018.
  41. ^ "More details emerge on Samsung's QD-OLED TV Plans | OLED-Info".
  42. ^ "Archived copy". Archived from the original on 2 January 2019. Retrieved 1 January 2019.{{cite web}}: CS1 maint: archived copy as title (link)
  43. ^ "TCL is developing hybrid QD-OLED display technology | OLED-Info".
  44. ^ Herald, The Korea (18 August 2019). "Samsung Display CEO affirms QD-OLED efforts". www.koreaherald.com.
  45. ^ "Samsung Display formally announces its $10.8 billion investment in QD-OLED TV production | OLED-Info".
  46. ^ Manners, David (11 October 2019). "Samsung to put $11bn into QD-OLED".
  47. ^ "Top Trends in Quantum Dots at SID Display Week 2019 – Part 2". 26 June 2019.
  48. ^ "Samsung Looking Beyond QD OLED". 28 November 2019.
  49. ^ "Samsung says its new quantum dot TV tech boosts image quality over regular OLED displays".
  50. ^ "Samsung Display's new QD-OLED panel can hit 1,000 nits brightness for improved HDR". 10 January 2022.
  51. ^ "[Press Release] Samsung QD-Display Globally Certified by SGS for Outstanding Picture Quality".
  52. ^ "Our TV Picture Quality Tests: Color Gamut".
  53. ^ a b "Samsung's Quantum Dot successor, QNED, could enter production in 2021". 16 July 2020.
  54. ^ "Are Quantum Nano Emitting Diodes (QNEDs) the Next Big Thing?". 8 April 2020.
  55. ^ "Are Quantum Nano Emitting Diodes (QNEDs) the Next Big Thing? - Display Supply Chain Consultants".
  56. ^ "Samsung's revolutionary QNED tech ready for mass production: Report". 16 November 2020.
  57. ^ "Samsung Display delays installment of pilot line for QNED". 12 May 2022.
  58. ^ "Channelnews : New Samsung LG Premium Display War, Nanorod QLED Tipped to be Superior to OLED".
  59. ^ Abella, Reycarlo (24 February 2023). "What Is QNED Explained: How It Compares To QLED & OLED". ScreenRant. Retrieved 28 December 2023.
  60. ^ "Mini LED vs. OLED: comparing the top TV technology". lg.com. Retrieved 28 December 2023.
  61. ^ "What is QLED? Demystifying the future of TV tech – Trusted Reviews". trustedreviews.com. 9 June 2016. Archived from the original on 11 July 2017. Retrieved 3 April 2018.
  62. ^ Palomaki, Peter (5 April 2018). "What's Next for Quantum Dots?". DisplayDaily. Archived from the original on 4 December 2023. Retrieved 14 January 2019.
  63. ^ Johnson, Dexter (21 November 2017). "Nanosys Wants Printing Quantum Dot Displays to be as Cheap as Printing a T-Shirt". IEEE Spectrum: Technology, Engineering, and Science News. Retrieved 14 January 2019.
  64. ^ "Peter Palomaki: The Evolution of Quantum Dot Technology". Samsung Display PID. 24 May 2018. Retrieved 14 January 2019.
  65. S2CID 4426602
    .
  66. S2CID 257231945
    .
  67. PMID 37236922
    .
  68. ^ Herald, The Korea (18 November 2014). "Quantum dot is no game changer: Merck". www.koreaherald.com.
  69. ^ "Merck leads a new consortium to develop quantum materials for light emission – OLED-Info". www.oled-info.com.
  70. ^ Palomaki, Peter (17 September 2018). "Germany Pushing the Boundaries of EL QLED with Consortium". www.displaydaily.com.
  71. ^ Palomaki, Peter (23 December 2019). "Bright. Long Lasting. Cd-Free. What Else Could You Want from EL-QLED?". DisplayDaily.
  72. ^ Taipei, Jessie Lin, DIGITIMES Research (7 November 2016). "Digitimes Research: Samsung Electronics developing QD technology toward QLED". digitimes.com. Retrieved 3 April 2018.{{cite web}}: CS1 maint: multiple names: authors list (link)
  73. ^ "CPT aims to start mass producing QD-LED displays within 2 years – OLED-Info". www.oled-info.com. Retrieved 3 April 2018.
  74. ^ "Digitimes Research: Samsung will begin QLED TV production in 2019 – OLED-Info". www.oled-info.com. Retrieved 3 April 2018.
  75. ^ a b Harding, Scharon (22 April 2024). "Meet QDEL, the backlight-less display tech that could replace OLED in premium TVs". Ars Technica. Retrieved 5 January 2024.
  76. ^ Cohen, Simon (15 January 2024). "Sharp secretly revealed the first QDEL TV at CES". Digital Trends. Retrieved 1 May 2024.
  77. ISBN 978-1-118-58581-8
    .
  78. ^ Ltd, SPIE Europe. "EU report sends mixed message on cadmium quantum dots". optics.org. Retrieved 3 April 2018.
  79. PMID 25961530
    .
  80. S2CID 205258576
    .
  81. S2CID 15829009
    .
  82. S2CID 94993172. Archived from the original
    (PDF) on 13 May 2016. Retrieved 30 April 2010.
  83. ^ "Samsung develops method for self-emissive QLED | ZDNet". www.zdnet.com.

External links

Retrieved from "https://en.wikipedia.org/w/index.php?title=Quantum_dot_display&oldid=1228203390"