Sunlike White Quantum Dot Light‐Emitting Diodes with High Color Rendition Quality

Abstract

implement white light-emission, especially compared to white OLEDs; the white OLEDs require a complicated multilayer structure to form blue/yellow or blue/ green/red emitting layers (EMLs). [9] Also, to change the emission peak wavelength for tuning the properties of white light, a new emitter molecule structure should be designed. On the contrary, white QLEDs can be simply fabricated with mixed colors of QDs in a single EML, [10-12] which makes their device structure and fabrication process as easy as monochromatic QLEDs. In addition, the spectral peak can be easily and precisely adjustable by changing the size of the QD core, enabling to tailor the characteristics of the white light, such as the color rendering index (CRI) and correlated color temperature (CCT). Owing to these advantages of QDs and QLEDs, a high color-quality lighting source based on white QLEDs can be achievable. Natural light from the sun is one of the best illuminants exhibiting a CRI of 100, meaning that any colors can be rendered over the entire visible spectral ranges (from red to violet). The sunlight also contains spectra essential for all organic creatures on earth. For instance, photosynthesis requires a variety of wavelengths depending on the types of chlorophylls. [13,14] The human circadian rhythm is also affected by the change of light intensity and color of the sunlight over time. [15-17] The lighting devices used in aquariums should contain short wavelengths of blue-violet colors to reproduce the natural underwater conditions as well as the other visible wavelengths to show the colors of creatures for visitors. In this wise, for a variety of purposes, it is undoubtedly demanded that artificial light sources show a "sunlike" emission spectrum as similar to the sunlight as possible. White OLEDs may have a high CRI of >85 but they are too costly due to the complicated fabrication process as mentioned above. Meanwhile, researches on white QLEDs have been increasing continuously since the first white QLED was demonstrated in 2004. [18-30] In particular, the Bulović group reported trichromatic QLEDs emitting white light solely from QDs by mixing red, green, and blue QDs in the EML in 2007. [18] The QD mixing method also has the advantages of simple processing and color tuning by changing the blending ratio between QDs. In 2014, the first tetrachromatic white QLED was demonstrated, showing the highest CRI of 93. [19] It was a meaningful result demonstrating a high CRI from white QLEDs consisting of narrow spectra of primary colors. Nevertheless, the spectrum is still dissimilar to the Although it is demanded for general lighting sources to have high color rendition qualities close to natural daylight, it is difficult to make sunlike artificial illuminants due to limited tunability of phosphors and complicated fabrication processes. On the contrary, white-emitting quantum dot (QD) light-emitting diodes (QLEDs) can be easily produced by mixing several colors of QDs in a single emitting layer (EML). In this work, sunlike white QLEDs showi...

Transient Dynamics of Charges and Excitons in Quantum Dot Light‐Emitting Diodes

“…[ 1–6 ] Among them, QD‐based light‐emitting diodes (QLEDs) have attracted great attention owing to superb color purity, high brightness and stability, and simple fabrication methods. [ 7–13 ] Furthermore, the external quantum efficiency (EQE) of QLEDs reached the theoretical limit (≈20%) as that of organic light‐emitting diodes, [ 14–17 ] increasing the possibility of using them for next‐generation displays and lighting devices. Nevertheless, the overall performance of QLEDs needs to be improved further to meet the conditions for commercialized products.…”

Synthesis of UV/blue light-emitting aluminum hydroxide with oxygen vacancy and their application to electrically driven light-emitting diodes

“…Luminescent inorganic materials, such as oxide-based inorganic phosphors, quantum dots, carbon dots, rare-earth phosphors, and metal hydroxides, have been researched for display, sensor technology, solar energy conversions, LEDs, bio-imaging, and more for their luminescent properties and chemical stability. 1–12 Among different luminescent materials, aluminum-related materials with bandgaps above 4.5 eV, such as aluminum oxide (Al 2 O 3 ), aluminum hydroxide (Al(OH) 3 ), and boehmite (AlOOH), have attracted attention due to their low cost, high stability, and non-toxicity. They have different origins of light emission from luminescent nanoparticles such as quantum dots which controlled the band gap between 1.2–3.5 eV depending on their size or shape ( i.e.…”

“…, quantum confinement effect). 8,10 Since defects and color centers in aluminum-related materials can substantially affect the materials' electrical, optical, and thermal properties, those materials have also been studied for applications of optoelectronic devices. 2,13–16 Especially, various polymorphs of an aluminum hydroxide such as gibbsite, bayerite, nordstrandite, and doyleite have been produced and applied to micro-organism and phosphate absorbents for waste treatment, antacid drugs, and flame retardant materials.…”

“…Additionally, luminescent Al(OH) 3− x nanoparticles we made were presented for the electrically driven active LEDs structure, which quantum dot-based LEDs research has been well known. 8,10,22–24 The Al(OH) 3− x based LEDs were efficiently fabricated by the solution processing method. The architecture of the active LEDs with Al(OH) 3− x emissive layers (EML) was ITO (cathode)/ZnO nanoparticle films (40 nm)/Al(OH) 3− x active layers (∼2 monolayers)/2,2′-bis(4-(carbazol-9-yl)phenyl)-biphenyl (BCBP, 50 nm)/MoO 3 (10 nm)/Al (100 nm).…”

Substantial Improvement of Color-Rendering Properties of Conventional White LEDs Using Remote-Type Red Quantum-Dot Caps

“…Other types of remote QD components have also been studied and applied to various lighting structures [ 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. These efforts showed that the color rendering characteristics can be improved substantially by adopting QD materials [ 24 ]. From the early stage of research of QD applications in lightings and displays, QD-polymer or QD-glass composites have been widely investigated by various groups [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ].…”