Himchan Cho

Organic-inorganic hybrid perovskites are emerging low-cost emitters with very high color purity, but their low luminescent efficiency is a critical drawback. We boosted the current efficiency (CE) of perovskite light-emitting diodes with a simple bilayer structure to 42.9 candela per ampere, similar to the CE of phosphorescent organic light-emitting diodes, with two modifications: We prevented the formation of metallic lead (Pb) atoms that cause strong exciton quenching through a small increase

Abstract Metal halide perovskites (MHPs) have numerous advantages as light emitters such as high photoluminescence quantum efficiency with a direct bandgap, very narrow emission linewidth, high charge‐carrier mobility, low energetic disorder, solution processability, simple color tuning, and low material cost. Based on these advantages, MHPs have recently shown unprecedented radical progress (maximum current efficiency from 0.3 to 42.9 cd A −1 ) in the field of light‐emitting diodes. However, pe

This paper reports highly bright and efficient CsPbBr 3 perovskite light‐emitting diodes (PeLEDs) fabricated by simple one‐step spin‐coating of uniform CsPbBr 3 polycrystalline layers on a self‐organized buffer hole injection layer and stoichiometry‐controlled CsPbBr 3 precursor solutions with an optimized concentration. The PeLEDs have maximum current efficiency of 5.39 cd A −1 and maximum luminance of 13752 cd m −2 . This paper also investigates the origin of current hysteresis, which can be a

Precise patterning of quantum dot (QD) layers is an important prerequisite for fabricating QD light-emitting diode (QLED) displays and other optoelectronic devices. However, conventional patterning methods cannot simultaneously meet the stringent requirements of resolution, throughput, and uniformity of the pattern profile while maintaining a high photoluminescence quantum yield (PLQY) of the patterned QD layers. Here, a specially designed nanocrystal ink is introduced, "photopatternable emissiv

We have achieved high-efficiency polycrystalline perovskite light-emitting diodes (PeLEDs) based on formamidinium (FA) and cesium (Cs) mixed cations without quantum dot synthesis. Uniform single-phase FA_{1- x}Cs _xPbBr₃ polycrystalline films were fabricated by one-step formation with various FA:Cs molar proportions; then the influences of chemical composition on film morphology, crystal structure, photoluminescence (PL), and electroluminescence (EL) were systematica

Abstract Organic nanofibers (ONFs) have attracted much interest as one‐dimensional functional units in various research fields with their unique advantages. Among many fabrication methods for them, electrospinning has been in the spotlight recently because of its simplicity and versatility. In this paper, first we introduce the principle, advantages, and conditions of electrospinning and then review recent studies about electronic and photonic applications of electrospun ONFs, including organic

We present a universal direct photocatalytic patterning method that can completely preserve the optical properties of perovskite nanocrystals (PeNCs) and other emissive nanomaterials. Solubility change of PeNCs is achieved mainly by a photoinduced thiol-ene click reaction between specially tailored surface ligands and a dual-role photocatalytic reagent, pentaerythritol tetrakis(3-mercaptopropionate) (PTMP), where the thiol-ene reaction is enabled at a low light intensity dose (~ 30 millijoules p

Direct optical lithography presents a promising patterning method for colloidal quantum dots (QDs). However, additional care needs to be taken to prevent deterioration of the optical properties of QDs upon patterning, especially for InP-based QDs. This study proposes an efficient method for high-resolution patterning of InP-based QDs using a photoacid generator while preserving their optical properties. Specifically, our solid-state ligand exchange strategy, replacing chloride ligands with long-

Abstract Augmented reality (AR) and virtual reality (VR) are emerging interactive technologies that realize the “metaverse,” leading to a totally new digital interactive experience in daily life in various aspects. In order to provide users with a more immersive experience, displays for AR/VR have rapidly evolved to achieve high resolutions and a large color gamut on small panels. Recently, nanoscale light emitters such as quantum dots (QDs) and metal halide perovskites (MHPs) with high photolum

Two-dimensional (2D) organic-inorganic halide perovskites (OIHPs) with an alternating stacked structure of an organic layer and an inorganic layer draw significant attention for photovoltaics, multiple quantum-well, and passivation of three-dimensional perovskites. Although the low-cost and simple spin-coating process of these materials offers a vast platform to study fundamental properties and help them achieve rapid progress in electronics and optoelectronics, chemical vapor deposition (CVD) g

This paper reports a comparative study of thermal stability between all-organic metal halide perovskite (MHP) CsPbBr3 and organic–inorganic hybrid MHP (methylammonium lead bromide MAPbBr3). The film morphology, crystal structure, steady-state photoluminescence intensity, and photoluminescence lifetime of CsPbBr3 and MAPbBr3 polycrystalline films were measured after thermal annealing at temperatures from 70°C to 230°C. The CsPbBr3 films exhibited little change in their structural and luminescent

Direct photolithography, which utilizes photosensitive quantum dot (QD) inks, is a powerful patterning method for implementing next-generation high-resolution QD displays. However, the chemical reactions occurring during the photoinduced solubility change process can damage the QDs’ surface, especially for InP QDs. In this study, we focus on a cleavable ligand-induced direct photolithography (CLIP) technique utilizing specially designed 3-((but-3-enoyloxy)methyl)-2-nitrobenzoic acid (BNA) ligand

We report improvement of hole injection efficiency of a graphene anode by tuning its work function (WF) via surface fluorination. We used chemical vapor deposition to synthesize high-quality graphene sheets and then treated them with CHF3 plasma to induce fluorination. We used x-ray photoelectron spectroscopy to examine the fluorine coverage and the kind of chemical bonds in fluorinated graphene (FG). Also, we used ultraviolet photoelectron spectroscopy to systematically study the changes in the

The development of precise, chemical‐free, and low‐cost pixel patterning with high resolution and throughput instead of conventional photolithography is very important for large‐area flexible organic light‐emitting diode (OLED) displays or solid‐state lightings with high aperture ratio. Here, a novel scalable and noninvasive lithography is reported as a pixel patterning method for OLEDs using highly aligned printed organic fiber arrays in large area. Use of electrohydrodynamic organic nanowire p

Europium halide perovskites are promising candidates for environmentally benign blue-light emitters with their narrow emission line width. However, the development of high-photoluminescence quantum yield (PLQY) colloidal europium halide perovskite nanocrystals (PNCs) is hindered by limited synthetic methods and elusive reaction mechanisms. Here, we provide an effective synthetic route for achieving high-PLQY deep-blue-emitting colloidal CsEuBr 3 PNCs. Using two Br-organic ligand precursors, oley