High-efficiency light-emitting devices based on quantum dots with tailored nanostructures

Abstract

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...

Interfacial engineering of core/shell heterostructured nanocrystal quantum dots for light-emitting applications

“…2 h for each CdS atomic layer shelling). To reduce the reaction time, a single-step synthetic method that utilizes the reactivity difference between the precursors has been proposed to realize composition gradients within heterostructured NQDs, and has been further optimized to control the composition profiles in a variety of heterostructures [5,21].…”

“…Therefore, thick-shell NQDs with engineered interfaces have been extensively studied as light-emitting materials. One representative achievement is thick-shell NQDs with composition gradient interfaces that outperform those of electroluminescence devices ( Figure 5(a,c,d)) [3,5,25]. As a result of the persistent efforts to tailor the formulations at the interfaces, quantum-dot light-emitting diodes with external quantum efficiencies of over 10% with green, blue, and red NQDs have been successfully realized ( Figure 5(b)) [5].…”

“…Nanocrystal quantum dots (NQDs) [1] exhibit narrow emissions upon a broad range of excitation wavelengths and high luminescence efficiencies, making them promising for use in various light-emitting applications, including displays [2][3][4][5][6][7][8][9][10][11], solar concentrators [12][13][14][15], and lasers [16][17][18]. In the last two decades, the structures of NQDs evolved into sophisticated heterostructures, boosting their optical performances and photophysical stabilities [19][20][21][22][23][24][25][26][27].…”

“…In addition, the potential profiles across the interfaces influence the Auger recombination (AR) rates [28,29,31,32]. Beyond gaining photophysical insights into the structure-property relationship, the advances in interfacial engineering have enabled the control of the optical properties of core/shell heterostructured NQDs and have led to substantial advances in their applications [5,24,33].…”

Comparative Analysis of Methods for Enhancement of the Photostability of CdTe@TGA QD Colloid Solutions

“…Semiconductor nanocrystals (colloid quantum dots (QD)) attract great attention in recent years due to numerous possible applications, e.g., in life science, [1][2][3] in sensorics, [4][5][6] in display technology, 7 as LEDs, 8,9 solar energy harvesting. [10][11][12] The progress in these studies is sometimes hindered by the limitations of chemical stability and photostability of QDs in solution.…”