Han, Tae Hee

This review outlines problems and progress in development of solution-processed organic light-emitting diodes (SOLEDs) in industry and academia. Solution processing has several advantages such as low consumption of materials, low-cost processing, and large-area manufacturing. However, use of a solution process entails complications, such as the need for solvent resistivity and solution-processable materials, and yields SOLEDs that have limited luminous efficiency, severe roll-off characteristics

Although solution processing of small-molecule organic light-emitting diodes (OLEDs) has been considered as a promising alternative to standard vacuum deposition requiring high material and processing cost, the devices have suffered from low luminous efficiency and difficulty of multilayer solution processing. Therefore, high efficiency should be achieved in simple-structured small-molecule OLEDs fabricated using a solution process. We report very efficient solution-processed simple-structured s

Abstract Mechanically resilient optoelectronic devices are relevant for a wide range of applications, including portable and wearable devices. Perovskite thin film‐based devices are a suitable choice for designing such resilient systems as it demonstrates high performance while preserving moderate mechanical compliance. Yet its mechanical property can be improved further by integrating the energy dissipation system and self‐healing ability into the thin film. Copolymers containing Lewis‐base fun

We report effective solution-processed chemical p-type doping of graphene using trifluoromethanesulfonic acid (CF3 SO3 H, TFMS), that can provide essential requirements to approach an ideal flexible graphene anode for practical applications: i) high optical transmittance, ii) low sheet resistance (70 % decrease), iii) high work function (0.83 eV increase), iv) smooth surface, and iv) air-stability at the same time. The TFMS-doped graphene formed nearly ohmic contact with a conventional organic h

Although the luminous efficiency has been significantly improved in multilayered organic light-emitting diodes (OLEDs), understanding the major factors that influence degradation of OLEDs remains a major challenge due to their complex device structure. In this regard, we elucidate the crucial role of hole injection layer (HIL) in degradation of OLEDs by using systematically controlled hole injection interfaces. To analyze charge injection dependent degradation mechanism of OLEDs, we fabricate mu

This paper introduces a method for improving the sensitivity to NO2 gas of a p-type metal oxide semiconductor gas sensor. The gas sensor was fabricated using CuO nanowires (NWs) grown through thermal oxidation and decorated with ZnO nanoparticles (NPs) using a sol-gel method. The CuO gas sensor with a ZnO heterojunction exhibited better sensitivity to NO2 gas than the pristine CuO gas sensor. The heterojunction in CuO/ZnO gas sensors caused a decrease in the width of the hole accumulation layer

We used various nondestructive analyses to investigate various host material systems in the emitting layer (EML) of simple-structured, green phosphorescent organic light-emitting diodes (OLEDs) to clarify how the host systems affect its luminous efficiency (LE) and operational stability. An OLED that has a unipolar single-host EML with conventional poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PEDOT: PSS) showed high operating voltage, low LE (∼26.6 cd/A, 13.7 lm/W), and short lifeti

With the rapid growth of the volume of spent Li-ion batteries (LIBs), recycling of spent LIBs has attracted significant attention in recent years for future sustainability. In particular, there remains a great need for the development of a scalable and environment-friendly separation process to recycle valuable cathode active materials from spent LIBs and electrode scraps. In this work, froth flotation technique was adopted to separate cathode active materials from a mixture of cathode and anode

The use of flexible organic light-emitting diodes (OLEDs) for the next-generation displays and solid-state lightings has been considered, but the widely used transparent conducting electrode (TCE), indium–tin-oxide (ITO), should be replaced by flexible electrodes due to its brittleness and increasing cost. Therefore, many kinds of alternative TCEs have been increasingly studied. In this paper, the properties and applications of the candidate transparent flexible electrodes classified into four c

Abstract Solution‐processed small‐molecule organic light‐emitting diodes (OLEDs) are regarded as next‐generation flat‐panel displays and solid‐state lighting sources due to low material loss and a simple device fabrication process. However, they still suffer from low device efficiency and severe efficiency roll‐off. Here, molecular‐scale strategies are proposed to achieve highly efficient solution‐processed small‐molecule OLEDs with reduced efficiency roll‐off. By combining experiments with ab i

Ultraviolet ozone (UVO) surface treatment of graphene changes its sp(2)-hybridized carbons to sp(3)-bonded carbons, and introduces oxygen-containing components. Oxidized graphene has a finite energy band gap, so UVO modification of the surface of a four-layered graphene anode increases its surface ionization potential up to similar to 5.2 eV and improves the hole injection efficiency (eta) in organic electronic devices by reducing the energy barrier between the graphene anode and overlying organ

Chemically synthesized colloidal metal halide perovskite (MHP) nanocrystals (NCs) have high luminous efficiency, but they have long-chain organic ligands bound perpendicularly to the surface, which impede charge injection and transport, thereby causing charge accumulation and consequent degradation. This work presents an in situ crystallization strategy for polycrystalline MHP light emitters by altering the surface chemistry of MHPs, followed by lateral surface capping with a linear ionic homopo

An iron based metal-nitrogen-carbon (MNC) type oxygen reduction reaction catalyst was tested for in-situ polarization performance and durability. High open circuit voltage (OCV) of ~0.97 V and high activities were observed. Current density around 750 mA/cm2 was obtained at 0.6 ViR-free/RHE and volumetric current density of 31 A/cm3 was obtained at 0.8 ViR-free. A significant decrease in polarization after start-stop durability test was observed for this catalyst. An attempt was made to recover t