There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The present invention provides a heterocyclic compound and an organic light-emitting device including the heterocyclic compound. The organic light-emitting devices using the heterocyclic compounds have high-efficiency, low driving voltage, high luminance and long lifespan.

Organic light-emitting device

We report the implementation of continuous, highly flexible, and transparent graphene films obtained by chemical vapor deposition (CVD) as transparent conductive electrodes (TCE) in organic photovoltaic cells. Graphene films were synthesized by CVD, transferred to transparent substrates, and evaluated in organic solar cell heterojunctions (TCE/poly-3,4-ethylenedioxythiophene:poly styrenesulfonate (PEDOT:PSS)/copper phthalocyanine/fullerene/bathocuproine/aluminum). Key to our success is the continuous nature of the CVD graphene films, which led to minimal surface roughness (∼0.9 nm) and offered sheet resistance down to 230 Ω/sq (at 72% transparency), much lower than stacked graphene flakes at similar transparency. In addition, solar cells with CVD graphene and indium tin oxide (ITO) electrodes were fabricated side-by-side on flexible polyethylene terephthalate (PET) substrates and were confirmed to offer comparable performance, with power conversion efficiencies (η) of 1.18 and 1.27%, respectively. Further...

Continuous, highly flexible, and transparent graphene films by chemical vapor deposition for organic photovoltaics.

We report the implementation of continuous, highlyflexible, and transparent graphenefilms obtained by chemical vapor deposition (CVD) as transparent conductive electrodes (TCE) in organic photovoltaic cells. Graphene films were synthesized by CVD, transferred to transparent substrates, and evaluated in organic solar cell heterojunctions (TCE/poly-3,4-ethylenedioxythiophene:poly styrenesulfonate (PEDOT:PSS)/copper phthalocyanine/fullerene/bathocuproine/aluminum). Key to our success is the continuous nature of the CVD graphenefilms,whichledtominimalsurfaceroughness(0.9nm)andofferedsheetresistancedownto230/ sq (at 72% transparency), much lower than stacked grapheneflakes at similar transparency. In addition, solar cellswithCVDgrapheneandindiumtinoxide(ITO)electrodeswerefabricatedside-by-sideonflexiblepolyethylene terephthalate (PET) substrates and were confirmed to offer comparable performance, with power conversion efficiencies()of1.18and1.27%,respectively.Furthermore,CVDgraphenesolarcellsdemonstratedoutstanding capability to operate under bending conditions up to 138°, whereas the ITO-based devices displayed cracks and irreversiblefailureunderbendingof60°.OurworkindicatesthegreatpotentialofCVDgraphenefilmsforflexible photovoltaic applications.

Continuous, Highly Flexible, and Transparent Graphene Films by Chemical Vapor Deposition for Organic

During the last few years, transition metal oxides (TMO) such as molybdenum tri-oxide (MoO3), vanadium pent-oxide (V2O5) or tungsten tri-oxide (WO3) have been extensively studied because of their exceptional electronic properties for charge injection and extraction in organic electronic devices. These unique properties have led to the performance enhancement of several types of devices and to a variety of novel applications. TMOs have been used to realize efficient and long-term stable p-type doping of wide band gap organic materials, charge-generation junctions for stacked organic light emitting diodes (OLED), sputtering buffer layers for semi-transparent devices, and organic photovoltaic (OPV) cells with improved charge extraction, enhanced power conversion efficiency and substantially improved long term stability. Energetics in general play a key role in advancing device structure and performance in organic electronics; however, the literature provides a very inconsistent picture of the electronic structure of TMOs and the resulting interpretation of their role as functional constituents in organic electronics. With this review we intend to clarify some of the existing misconceptions. An overview of TMO-based device architectures ranging from transparent OLEDs to tandem OPV cells is also given. Various TMO film deposition methods are reviewed, addressing vacuum evaporation and recent approaches for solution-based processing. The specific properties of the resulting materials and their role as functional layers in organic devices are discussed.

Transition Metal Oxides for Organic Electronics: Energetics, Device Physics and Applications

Criteria for ITO (indium tin-oxide) thin film as the bottom electrode of an organic light emitting diode

We investigated the optical properties of a dielec-tric−metal−dielectric multilayer for the transparent top cathode in top-emitting organic light emitting diodes (TOLEDs). The optical transmittance of the metal layer was enhanced by depositing a dielectric material which had a high refraction index n below and above the metal (Ag) layer. Due to multiple reflections and interferences, the Ag layer sandwiched between dielectric materials with a high value of n can show improved transmittance. Because the WO3 had a high value of n (>2.0), a thin WO3 layer could fulfill the optimum zero-reflection condition with an Ag metal layer. Thus, a WO3/Ag/WO3 multilayer should have high transmittance with a low sheet resistance. The optimum thicknesses of both Ag and WO3 to obtain the best transmittance value were determined by theoretical calculation, and they agreed well with the experimental results. The best results were obtained for the thermally evaporated WO3 (300 A)/Ag (120 A)/WO3 (300 A) structure, a high tran...

Optical Properties of WO3/Ag/WO3 Multilayer As Transparent Cathode in Top-Emitting Organic Light Emitting Diodes

We report the change of surface electronic structure of indium–tin–oxide (ITO) as a function of ultraviolet (UV)–ozone treatment time. The voltage of organic light emitting diodes at a current density of 100 mA/cm2 was reduced as the surface treatment time using UV–ozone was lengthened. X-ray photoelectron spectroscopy results showed that the relative concentration of carbon atoms decreased, but oxygen concentration increased relatively with UV–ozone treatment. This led to the increase in the ITO work function via the reduction of operation voltage.

Effect of ultraviolet-ozone treatment of indium-tin-oxide on electrical properties of organic light emitting diodes

The effects of O2 inductively coupled plasma (ICP) treatment on the chemical composition and work function of indium-tin-oxide (ITO) surface were investigated. Synchrotron radiation photoemission spectroscopy showed that the O2 ICP treatment resulted in the increase of the ITO work function by 0.8 eV. Incorporation of oxygen atoms near the ITO surface during the ICP treatment induced a peroxidic ITO surface, increasing the work function. The enhanced oxidation of a thin Ni overlayer on the O2-ICP-treated sample suggests that preventing the migration of oxygen atoms into the active region of organic light-emitting diodes is important for improving device lifetime.

Mechanism for the increase of indium-tin-oxide work function by O2 inductively coupled plasma treatment

The relationship between surface roughness of indium tin oxide (ITO) and leakage current of organic light-emitting diode (OLED) was investigated. The surface roughness of ITO was measured with atomic force microscope (AFM) before the device fabrication by using these substrates, OLEDs were fabricated and their electrical properties were measured. leakage current of OLEDs depending on the surface roughness of the substrate. In this letter, we report that leakage currents of OLEDs are highly dependent on the peak-to-valley roughness (Rpv) of ITO.

https://iopscience.iop.org/article/10.1143/JJAP.42.L438/pdf

Yoon-Heung Tak

Papers

Criteria for ITO (indium tin-oxide) thin film as the bottom electrode of an organic light emitting diode

Optical Properties of WO3/Ag/WO3 Multilayer As Transparent Cathode in Top-Emitting Organic Light Emitting Diodes

Effect of ultraviolet-ozone treatment of indium-tin-oxide on electrical properties of organic light emitting diodes

Mechanism for the increase of indium-tin-oxide work function by O2 inductively coupled plasma treatment

Relationship between Surface Roughness of Indium Tin Oxide and Leakage Current of Organic Light-Emitting Diode