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Author

Yongwoo Kwon

Other affiliations: Samsung, Northwestern University
Bio: Yongwoo Kwon is an academic researcher from Hongik University. The author has contributed to research in topics: Materials science & Resistive random-access memory. The author has an hindex of 13, co-authored 33 publications receiving 859 citations. Previous affiliations of Yongwoo Kwon include Samsung & Northwestern University.

Papers
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Journal ArticleDOI
25 Apr 2014-ACS Nano
TL;DR: It is found that the presence of an additional ZnS shell makes a profound impact on device performances such as luminance and efficiencies, specifically showing unprecedented values of peak current efficiency of 46.4 cd/A and external quantum efficiency of 12.6%.
Abstract: Green CdSe@ZnS quantum dots (QDs) of 9.5 nm size with a composition gradient shell are first prepared by a single-step synthetic approach, and then 12.7 nm CdSe@ZnS/ZnS QDs, the largest among ZnS-shelled visible-emitting QDs available to date, are obtained through the overcoating of an additional 1.6 nm thick ZnS shell. Two QDs of CdSe@ZnS and CdSe@ZnS/ZnS are incorporated into the solution-processed hybrid QD-based light-emitting diode (QLED) structure, where the QD emissive layer (EML) is sandwiched by poly(9-vinlycarbazole) and ZnO nanoparticles as hole and electron-transport layers, respectively. We find that the presence of an additional ZnS shell makes a profound impact on device performances such as luminance and efficiencies. Compared to CdSe@ZnS QD-based devices the efficiencies of CdSe@ZnS/ZnS QD-based devices are overwhelmingly higher, specifically showing unprecedented values of peak current efficiency of 46.4 cd/A and external quantum efficiency of 12.6%. Such excellent results are likely att...

289 citations

Journal ArticleDOI
TL;DR: A performance-enhanced OHP resistive switching device that shows an excellent performance as insulating layers in Ag/CH3NH3PbI3/Pt cells, with an endurance of over 103 cycles, a high on/off ratio of 106, and an operation speed of 640 μs and without electroforming is reported.
Abstract: It was demonstrated that organolead halide perovskites (OHPs) show a resistive switching behavior with an ultralow electric field of a few kilovolts per centimeter. However, a slow switching time and relatively short endurance remain major obstacles for the realization of the next-generation memory. Here, we report a performance-enhanced OHP resistive switching device. To fabricate topologically and electronically improved OHP thin films, we added hydroiodic acid solution (for an additive) in the precursor solution of the OHP. With drastically improved morphology such as small grain size, low peak-to-valley depth, and precise thickness, the OHP thin films showed an excellent performance as insulating layers in Ag/CH3NH3PbI3/Pt cells, with an endurance of over 103 cycles, a high on/off ratio of 106, and an operation speed of 640 μs and without electroforming. We suggest plausible resistive switching and conduction mechanisms with current–voltage characteristics measured at various temperatures and with dif...

124 citations

Proceedings ArticleDOI
01 Dec 2011
TL;DR: In this paper, the authors reported characteristics of 20nm PRAM cell with optimized diode integration process and improved implantation technology to satisfy the required diode on current (Ion) with low off-current (Ioff).
Abstract: We reported characteristics of 20nm PRAM cell. Optimization of diode integration process and improved implantation technology were used to satisfy the required diode on-current (Ion) with low off-current (Ioff). Confined cell structure and novel bottom electrode (BE) materials were developed to reduce a reset current (Ireset) below 100uA. Using the advanced technologies, we successfully produced fully integrated 20nm node size PRAM device for the first time.

95 citations

Journal ArticleDOI
10 Jun 2014-ACS Nano
TL;DR: The origin of the initial irreversible capacity loss from the first lithiation process was addressed through probing changes in the electronic and structural properties of hollow-structured Co3O4 nanoparticles (NPs) during lithiation and delithiation using electrochemical Co 3O4 transistor devices that function as a Co3 O4 Li-ion battery.
Abstract: Origins of the irreversible capacity loss were addressed through probing changes in the electronic and structural properties of hollow-structured Co3O4 nanoparticles (NPs) during lithiation and delithiation using electrochemical Co3O4 transistor devices that function as a Co3O4 Li-ion battery. Additive-free Co3O4 NPs were assembled into a Li-ion battery, allowing us to isolate and explore the effects of the Co and Li2O formation/decomposition conversion reactions on the electrical and structural degradation within Co3O4 NP films. NP films ranging between a single monolayer and multilayered film hundreds of nanometers thick prepared with blade-coating and electrophoretic deposition methods, respectively, were embedded in the transistor devices for in situ conduction measurements as a function of battery cycles. During battery operation, the electronic and structural properties of Co3O4 NP films in the bulk, Co3O4/electrolyte, and Co3O4/current collector interfaces were spatially mapped to address the origi...

89 citations

Journal ArticleDOI
TL;DR: In this article, a color-pure green-and red-emitting non-Cd InP/ZnS core/shell quantum dots (QDs) and their utilization as color converters for the fabrication of display backlighting QD-based white light emitting diode (LED) was reported.
Abstract: This work reported on synthesis of highly efficient, color-pure green- and red-emitting non-Cd InP/ZnS core/shell quantum dots (QDs) and their utilization as color converters for the fabrication of display backlighting QD-based white light-emitting diode (LED). Green and red QD emitters were first individually embedded into a transparent polymeric matrix of polyvinylpyrrolidone and the resulting two free-standing QD composite plates were then physically combined into a bilayered form. White QD-LED was fabricated by remotely loading the bilayered QD plate of a red-on-green configuration onto blue LED chip. This remote-type white device generated a spectrally well-resolved, tricolored electroluminescent spectrum, and exhibited luminous efficacies of 8.9−16.7 lm/W, depending on forward currents of 20−100 mA, and a high color gamut of 87%.

60 citations


Cited by
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Journal ArticleDOI
TL;DR: The demonstration of these novel quantum-dot light-emitting diodes based on all-inorganic perovskite CsPbX3 (X = Cl, Br, I) nanocrystals opens a new avenue toward designing optoelectronic devices, such as displays, photodetectors, solar cells, and lasers.
Abstract: Novel quantum-dot light-emitting diodes based on all-inorganic perovskite CsPbX3 (X = Cl, Br, I) nanocrystals are reported. The well-dispersed, single-crystal quantum dots (QDs) exhibit high quantum yields, and tunable light emission wavelength. The demonstration of these novel perovskite QDs opens a new avenue toward designing optoelectronic devices, such as displays, photodetectors, solar cells, and lasers.

2,311 citations

Journal ArticleDOI
06 Nov 2014-Nature
TL;DR: This optoelectronic performance is achieved by inserting an insulating layer between the quantum dot layer and the oxide electron-transport layer to optimize charge balance in the device and preserve the superior emissive properties of the quantum dots.
Abstract: Solution-processed optoelectronic and electronic devices are attractive owing to the potential for low-cost fabrication of large-area devices and the compatibility with lightweight, flexible plastic substrates. Solution-processed light-emitting diodes (LEDs) using conjugated polymers or quantum dots as emitters have attracted great interest over the past two decades. However, the overall performance of solution-processed LEDs--including their efficiency, efficiency roll-off at high current densities, turn-on voltage and lifetime under operational conditions-remains inferior to that of the best vacuum-deposited organic LEDs. Here we report a solution-processed, multilayer quantum-dot-based LED with excellent performance and reproducibility. It exhibits colour-saturated deep-red emission, sub-bandgap turn-on at 1.7 volts, high external quantum efficiencies of up to 20.5 per cent, low efficiency roll-off (up to 15.1 per cent of the external quantum efficiency at 100 mA cm(-2)), and a long operational lifetime of more than 100,000 hours at 100 cd m(-2), making this device the best-performing solution-processed red LED so far, comparable to state-of-the-art vacuum-deposited organic LEDs. This optoelectronic performance is achieved by inserting an insulating layer between the quantum dot layer and the oxide electron-transport layer to optimize charge balance in the device and preserve the superior emissive properties of the quantum dots. We anticipate that our results will be a starting point for further research, leading to high-performance, all-solution-processed quantum-dot-based LEDs ideal for next-generation display and solid-state lighting technologies.

1,958 citations

Journal ArticleDOI
TL;DR: In this paper, a room-temperature (RT) synthesis of CsPbX3@X quantum-well band alignment is proposed to guarantee the excitons generation and high-rate radiative recombination at RT.
Abstract: Recently, Kovalenko and co-workers and Li and co-workers developed CsPbX3 (X = Cl, Br, I) inorganic perovskite quantum dots (IPQDs), which exhibited ultrahigh photoluminescence (PL) quantum yields (QYs), low-threshold lasing, and multicolor electroluminescence. However, the usual synthesis needs high temperature, inert gas protection, and localized injection operation, which are severely against applications. Moreover, the so unexpectedly high QYs are very confusing. Here, for the first time, the IPQDs' room-temperature (RT) synthesis, superior PL, underlying origins and potentials in lighting and displays are reported. The synthesis is designed according to supersaturated recrystallization (SR), which is operated at RT, within few seconds, free from inert gas and injection operation. Although formed at RT, IPQDs' PLs have QYs of 80%, 95%, 70%, and FWHMs of 35, 20, and 18 nm for red, green, and blue emissions. As to the origins, the observed 40 meV exciton binding energy, halogen self-passivation effect, and CsPbX3@X quantum-well band alignment are proposed to guarantee the excitons generation and high-rate radiative recombination at RT. Moreover, such superior optical merits endow them with promising potentials in lighting and displays, which are primarily demonstrated by the white light-emitting diodes with tunable color temperature and wide color gamut.

1,932 citations

Journal ArticleDOI
TL;DR: In this paper, a red, green and blue quantum-dot LEDs are realized by customizing the nanostructure of the quantum dots. But their performance was not as good as those of traditional LEDs.
Abstract: Bright, efficient red, green and blue quantum-dot LEDs are realized by customizing the nanostructure of the quantum dots.

832 citations

Journal ArticleDOI
TL;DR: A white light-emitting diode (0.33, 0.33) is fabricated using perovskite quantum dot/silica composites and is shown to have greatly improved stability.
Abstract: A white light-emitting diode (0.33, 0.33) is fabricated using perovskite quantum dot/silica composites. It is shown to have greatly improved stability.

733 citations