We report a full series of blue, green and red quantum-dot-based light-emitting devices (QD-LEDs), all with high external quantum efficiencies over 10%. We show that the fine nanostructure of quantum dots-especially the composition of the graded intermediate shell and the thickness of the outer shell-plays a very important role in determining QD-LED device performance due to its effects on charge injection, transport and recombination. These simple devices have maximum current and external quantum efficiencies of 63 cd A −1 and 14.5% for green QD-LEDs, 15 cd A −1 and 12.0% for red devices, and 4.4 cd A −1 and 10.7% for blue devices, all of which are well maintained over a wide range of luminances from 10 2 to 10 4 cd m −2 . All the QD-LEDs are solution-processed for ease of mass production, and have low turn-on voltages and saturated pure colours. The green and red devices exhibit lifetimes of more than 90,000 and 300,000 h, respectively. Since their inception about three decades ago 1-3 , semiconductor quantum dots have been intensively investigated because of their unique optical properties, including size-controlled tunable emission wavelength (known as the 'quantum confinement effect'), narrow emission spectra, high luminescent efficiency and colloidal-based synthesis process 4-7 . All these attractive characteristics make quantum dots excellent candidates for the development of next-generation display technologies. Quantum dot-based lightemitting diodes (QD-LEDs) have been demonstrated recently, and may offer many advantages over conventional LED and organic LED (OLEDs) technologies in terms of colour purity, stability and production cost, while still achieving similar levels of efficiency. To date, however, the electroluminescence efficiencies of QD-LEDs have remained significantly below those of OLEDs, despite steady progress in recent years [8][9][10][11][12][13][14][15][16][17] . Recently, an efficient deep-blue QD-LED has been reported that makes use of solutionprocessed poly(3,4-ethylenedioxythiophene):polystyrene sulphonate (PEDOT:PSS) and poly(N-vinyl carbazole) (PVK) as its hole injection and transport layers (HIL and HTL), respectively, and ZnO nanoparticles as its electron transport layer (ETL), and achieves a maximum external quantum efficiency (η EQE ) of 7.1% (ref. 15). The same device structure was also used to achieve a green QD-LED with an η EQE of 12.6% (ref. 17). Highly efficient red QD-LEDs with η EQE = 18-20% have been realized using an inverted device structure containing a vacuum-deposited HIL and HTL 16 , and also in another arrangement using a thin insulating layer to obtain an enhanced charge balance 18 . These are the first times that the performances of QD-LEDs have been comparable to those of state-of-the-art phosphorescent OLEDs 19-21 .It is noted that although high efficiencies have been achieved with blue (B), green (G) and red (R) QD-LEDs, these singlecolour QD-LEDs, developed by different research groups, commonly involve very different quantum dot preparation procedures (fo...

Colloidal quantum dot-polymer hybrid light emitting diodes (QLEDs) that exhibit external quantum efficiencies >12% for all three primary colors (21% from green) have been demonstrated. These high efficiencies result in part from a positive aging effect reported here for the first time, where positive aging means the efficiency of the QLED increased with time. We have achieved 470 h operational life time (T) at 2550 nits for red QLEDs. At longer times, negative aging phenomena lead to lower luminance and limit the lifetime of the QLEDs. It is concluded that we have reasonable control over the efficiency of QLEDs. The next challenge is to achieve lifetimes sufficiently long for all three primary colors for applications such as in television and illumination.

High‐quality violet‐blue emitting ZnxCd1‐xS/ZnS core/shell quantum dots (QDs) are synthesized by a new method, called “nucleation at low temperature/shell growth at high temperature”. The resulting nearly monodisperse ZnxCd1‐xS/ZnS core/shell QDs have high PL quantum yield (near to 100%), high color purity (FWHM) <25 nm), good color tunability in the violet‐blue optical window from 400 to 470 nm, and good chemical/photochemical stability. More importantly, the new well‐established protocols are easy to apply to large‐scale synthesis; around 37 g ZnxCd1‐xS/ZnS core/shell QDs can be easily synthesized in one batch reaction. Highly efficient deep‐blue quantum dot‐based light‐emitting diodes (QD‐LEDs) are demonstrated by employing the ZnxCd1‐xS/ZnS core/shell QDs as emitters. The bright and efficient QD‐LEDs show a maximum luminance up to 4100 cd m−2, and peak external quantum efficiency (EQE) of 3.8%, corresponding to 1.13 cd A−1 in luminous efficiency. Such high value of the peak EQE can be comparable with OLED technology. These results signify a remarkable progress, not only in the synthesis of high‐quality QDs but also in QD‐LEDs that offer a practicle platform for the realization of QD‐based violet‐blue display and lighting.