Sung-Hoon Lee

We report highly bright and efficient inverted structure quantum dot (QD) based light-emitting diodes (QLEDs) by using solution-processed ZnO nanoparticles as the electron injection/transport layer and by optimizing energy levels with the organic hole transport layer. We have successfully demonstrated highly bright red, green, and blue QLEDs showing maximum luminances up to 23,040, 218,800, and 2250 cd/m(2), and external quantum efficiencies of 7.3, 5.8, and 1.7%, respectively. It is also notice

We demonstrate a single-step synthetic method for highly luminescent (i.e., quantum yield up to 80%) and stable quantum dots (QDs) by using the reactivity difference between Cd and Zn precursors and that between Se and S precursors. A wide range of emission wavelengths (500−610 nm) with a narrow fwhm (<35 nm) is obtained by changing the ratios of the precursors. Under the reaction conditions selected, Cd- and Se (with a bit of S)-based cores are formed first and Zn- and S-based shells are formed

We demonstrate bright, efficient, and environmentally benign InP quantum dot (QD)-based light-emitting diodes (QLEDs) through the direct charge carrier injection into QDs and the efficient radiative exciton recombination within QDs. The direct exciton formation within QDs is facilitated by an adoption of a solution-processed, thin conjugated polyelectrolyte layer, which reduces the electron injection barrier between cathode and QDs via vacuum level shift and promotes the charge carrier balance w

Utilizing the reactivity difference between TOPSe and TOPS, we synthesized InP@ZnSeS QDs with the composition gradient in a radial direction where ZnSe alleviated lattice strain and ZnS protected QDs from degradation so that we achieved QDs with high QE and photo/chemical stability. In terms of systematic investigation on the relationship between the shell nanostructure and QD stability, we demonstrated that QDs with thick gradient shells exhibited high QE and much enhanced stability against the

Highly efficient green-light-emitting diodes (LEDs) based on [email protected] quantum dots (QDs) with a chemical-composition gradient are demonstrated. Through the moderate control of QD coverage in multilayered devices, excellent device performance has been achieved. The color-saturated green-light emission (see figure for Commission Internationale de l'Eclairage (CIE) co-ordinates) is mainly from the QD layers (more than 99% of total emission). Detailed facts of importance to specialist reade

The new deep-blue iridium(III) complexes, (TF)2Ir(pic), (TF)2Ir(fptz), (HF)2Ir(pic), and (HF)2Ir(fptz), consisting of 2',4″-difluororphenyl-3-methylpyridine with trifluoromethyl carbonyl or heptafluoropropyl carbonyl at the 3' position as the main ligand and a picolinate or a trifluoromethylated-triazole as the ancillary ligand, were synthesized and characterized for applications in organic light-emitting diodes (OLEDs). Density function theory (DFT) calculations showed that these iridium comple

A systematic analysis of the exciton-recombination zone within all-quantum dot (QD) multilayer films prepared by a layer-by-layer assembly method was made, using sensing QD layers in QD-based light-emitting diodes (QLEDs). Large area practical multicolored colloidal QLEDs were also demonstrated by patterning and placing variously colored QDs (red, orange, yellow-green, and green) in the exciton-recombination zone.

Bright, low-voltage driven colloidal quantum dot (QD)-based white light-emitting devices (LEDs) with practicable device performances are enabled by the direct exciton formation within quantum-dot active layers in a hybrid device structure. Detailed device characterization reveals that white-QLEDs can be rationalized as a parallel circuit, in which different QDs are connected through the same set of electrically common organic and inorganic charge transport layers.

Abstract An exciplex forming co‐host is introduced in order to fabricate orange organic light‐emitting diodes (OLEDs) with high efficiency, low driving voltage and an extremely low efficiency roll‐off, by the co‐doping of green and red emitting phosphorescence dyes in the host. The orange OLEDs achieves a low turn‐on voltage of 2.4 V, which is equivalent to the triplet energy gap of the phosphorescent‐green emitting dopant, and a very high external quantum efficiency (EQE) of 25.0%. Moreover, th

Filament light bulbs and halogen lamps are widely used to light houses and offices but are energy inefficient. We synthesized optimal phosphors for 460 nm blue light-emitting diodes (LEDs) and fabricated white LEDs to develop energy-efficient, reliable, and long-lived solid-state lighting LED devices. GaN-based blue LEDs are the excitation source for yttrium aluminum garnet: phosphors, and the phosphors convert the blue light into red and green lights. We take combinatorial chemistry method as a

We demonstrated a facile synthesis of highly luminescent blue emitting Cd 1− x Zn x S/ZnS core/shell structured nanocrystals (NCs) in straightforward and reproducible manner. The alloyed Cd 1− x Zn x S cores with homogeneity in both size and composition were prepared by introducing S precursors (S dissolved in the noncoordinating solvent (1-octadecene)) into the mixed solution of Cd−Oleate (Cd(OA) 2 ) and Zn−Oleate (Zn(OA) 2 ) at elevated temperature (300 °C). ZnS shells were successively overco

The formation of self-organized regular arrays of oxide nanotubes lies in a delicate balance between the oxide growth rate and the oxide etching rate and a lattice mismatch between the grown metal oxide and the underlying valve metal. The requisites for their fabrication are the electropolishing and a two-step anodization. The most uniform and self-organized regular arrays of anodic TiO2 nanotubes among those known so far are reported as another example of valve metal oxide nanotube arrays since

Tandem white organic light-emitting diodes (WOLEDs) using horizontally oriented phosphorescent dyes in an exciplex-forming co-host are presented, along with an orange OLED. A high external quantum efficiency of 32% is achieved for the orange OLED at 1000 cd m(-2) and the tandem WOLEDs exhibit a high maximum EQE of 54.3% (PE of 63 lm W(-1)).

Abstract The rate‐limiting step of charge generation in charge‐generation units (CGUs) composed of a p‐doped hole‐transporting layer (p‐HTL), 1,4,5,8,9,11‐hexaazatriphenylene hexacarbonitrile (HATCN) and n‐doped electron‐transporting layer (n‐ETL), where 1,1‐bis‐(4‐bis(4‐methyl‐phenyl)‐amino‐phenyl)‐cyclohexane (TAPC) was used as the HTL is reported. Energy level alignment determined by the capacitance–voltage ( C – V ) measurements and the current density–voltage characteristics of the structur

Thin-film ultraviolet (UV) light-emitting diodes (LEDs) with emission wavelengths below 400 nm are emerging as promising light sources for various purposes, from our daily lives to industrial applications. However, current thin-film UV-emitting devices radiate not only UV light but also visible light. Here, we introduce genuine UV-emitting colloidal nanocrystal quantum dot (NQD) LEDs (QLEDs) using precisely controlled NQDs consisting of a 2.5-nm-sized CdZnS ternary core and a ZnS shell. The effe