Jin-A Jeong

Highly flexible and transparent InZnSnOx∕Ag∕InZnSnOx multilayer electrode for flexible organic light emitting diodes

By inserting a very thin layer of Ag between two layers of amorphous indium zinc tin oxide (IZTO), we fabricated a highly flexible, low resistance, and highly transparent IZTO-Ag-IZTO multilayer electrode on a polyethylene terephthalate (PET) substrate. Due to surface plasmon resonance (SPR) effects and the ductility of the Ag layer, the IZTO-Ag-IZTO electrode exhibited a low sheet resistance of 4.99Ω∕sq. and a high transparency of 86% as well as superior flexibility despite the very thin thickness of the IZTO layer (30nm). It was found that the transition of the Ag layer from distinct islands to a continuous film occurred at a critical thickness (∼14nm). Continuity of the Ag film is very important for SPR in IZTO-Ag-IZTO electrode. The current density-voltage-luminance characteristics of flexible organic light emitting diodes (OLEDs) fabricated on IZTO-Ag-IZTO/PET were better than those of flexible OLEDs fabricated on an ITO/PET substrate due to the low sheet resistance and high work function of the IZTO.

Comparison of electrical, optical, structural, and interface properties of IZO-Ag-IZO and IZO-Au-IZO multilayer electrodes for organic photovoltaics

We compared the electrical, optical, structural, and interface properties of indium zinc oxide (IZO)-Ag-IZO and IZO-Au-IZO multilayer electrodes, as well as the dependence of their electrical and optical properties on the thicknesses of the Ag and Au layers when used for organic solar cells (OSCs). Even though all deposition processes were carried out at room temperature, the IZO-Ag (14 nm)-IZO and IZO-Au (12 nm)-IZO multilayer electrodes exhibited extremely low sheet resistances of 4.15 and 5.49 Ω/sq, and resistivities of 3.9×10−5 and 5.5×10−5 Ω cm, respectively. In spite of its similar electrical properties, the optical transmittance of the IZO-Ag-IZO electrode is much higher than that of the IZO-Au-IZO electrode, due to the more effective antireflection effect of Ag than Au in the visible region. In addition, synchrotron x-ray scattering and scanning electron microscopy examinations showed that the structure and morphology of the Ag and Au layers critically depend on their thicknesses. Moreover, the bu...

Comparative Investigation of Transparent ITO/Ag/ITO and ITO/Cu/ITO Electrodes Grown by Dual-Target DC Sputtering for Organic Photovoltaics

We investigated the characteristics of transparent indium tin oxide (ITO)/Ag/ITO (IAI) and ITO/Cu/ITO (ICI) multilayer electrodes grown by continuous dual-target dc sputtering for bulk heterojunction organic solar cells (OSCs). The IAI and ICI multilayer electrodes show a significant reduction in their sheet resistance and resistivity with increasing thickness of the Ag and Cu layers, respectively, despite the very small thickness of ITO (80 nm). However, the IAI electrode exhibits a much higher optical transmittance in the visible wavelength region under optimized conditions due to the more effective surface plasmon resonance of the Ag layer than that of the Cu layer. The Auger electron spectroscopy depth profile results for the IAI and ICI electrodes show that there is no severe interfacial reaction between the metal (Ag or Cu) layers and the ITO layers due to the high formation enthalpy of the Ag-O and Cu-O phases at room temperature. Moreover, the OSC fabricated on the IAI electrode shows a higher power conversion efficiency (3.26%) than the OSC prepared on the ICI electrode (2.78%) due to its high optical transmittance in the region of 400-600 nm corresponding to the absorption wavelength range of the organic active layer. This indicates that the IAI multilayer electrode is a promising transparent conducting electrode for OSCs or flexible OSCs due to its very low resistivity and high optical transmittance in the 400-600 nm range.

Flexible Al-doped ZnO films grown on PET substrates using linear facing target sputtering for flexible OLEDs

We report the characteristics of flexible Al-doped zinc oxide (AZO) films prepared by a plasma damage-free linear facing target sputtering (LFTS) system on PET substrates for use as a flexible transparent conducting electrode in flexible organic light-emitting diodes (OLEDs). The electrical, optical and structural properties of LFTS-grown flexible AZO electrodes were investigated as a function of dc power. We obtained a flexible AZO film with a sheet resistance of 39 Ω/ and an average transmittance of 84.86% in the visible range although it was sputtered at room temperature without activation of the Al dopant. Due to the effective confinement of the high-density plasma between the facing AZO targets, the AZO film was deposited on the PET substrate without plasma damage and substrate heating caused by bombardment of energy particles. Moreover, the flexible OLED fabricated on the AZO/PET substrate showed performance similar to the OLED fabricated on a ITO/PET substrate in spite of a lower work function. This indicates that LFTS is a promising plasma damage-free and low-temperature sputtering technique for deposition of flexible and indium-free AZO electrodes for use in cost-efficient flexible OLEDs.

Room-Temperature Indium-Free Ga:ZnO/Ag/Ga:ZnO Multilayer Electrode for Organic Solar Cell Applications

Table I. Comparison of electrical and optical properties of asgrown GZO (amorphous), GZO annealed at 500°C (crystalline), and GZO/Ag/GZO (amorphous) multilayer electrodes prepared at room temperature.

Enhancement of hole injection using ozone treated Ag nanodots dispersed on indium tin oxide anode for organic light emitting diodes

The authors report the enhancement of hole injection using an indium tin oxide (ITO) anode covered with ultraviolet (UV) ozone-treated Ag nanodots for fac tris (2-phenylpyridine) iridium Ir(ppy)3-doped phosphorescent organic light-emitting diodes (OLEDs). X-ray photoelectron spectroscopy and UV-visible spectrometer analysis exhibit that UV-ozone treatment of the Ag nanodots dispersed on the ITO anode leads to formation of Ag2O nanodots with high work function and high transparency. Phosphorescent OLEDs fabricated on the Ag2O nanodot-dispersed ITO anode showed a lower turn-on voltage and higher luminescence than those of OLEDs prepared with a commercial ITO anode. It was thought that, as Ag nanodots changed to Ag2O nanodots by UV-ozone treatment, the decrease of the energy barrier height led to the enhancement of hole injection in the phosphorescent OLEDs.

Effect of Ag interlayer on the optical and passivation properties of flexible and transparent Al2O3∕Ag∕Al2O3 multilayer

We report on the characteristics of a flexible Al2O3∕Ag∕Al2O3 multilayer passivation grown on a polyethylene terephthalate (PET) substrate as a function of Ag thickness. Due to the surface plasmon resonance (SPR) effects and the ductility of the Ag layer that is sandwiched between the dielectric Al2O3 layer, the flexible Al2O3∕Ag∕Al2O3 multilayer passivation exhibits a high transparency of 86.44% and improved flexibility at a Ag thickness of 10nm. We found that SPR effects in the Ag layer occur at the transition region from distinct islands to a continuous film at a critical thickness (∼10nm). In addition, the water vapor transmission rate of the Al2O3∕Ag∕Al2O3∕PET sample decreased as the thickness of the Ag layer increased. Using synchrotron x-ray scattering and field emission scanning electron microscopy, we suggest a possible mechanism to explain the SPR in the Ag layer of the flexible and transparent Al2O3∕Ag∕Al2O3 multilayer passivation.

Low‐resistivity transparent In2O3 films prepared by reactive ion plating

Indium oxide films with an electrical resistivity of less than 1.5×10−4 Ω cm and good optical quality were prepared by the reactive ion plating of pure indium in an oxygen atmosphere of ∼10−4 Torr. The deposition rate was in the range of 500–900 A/min, which is much higher than that of the ordinary evaporation. Hall effect measurement showed that the observed low resistivity is primarily due to the high electron mobility (≥70 cm2/V s) with carrier density up to 7×1020/cm3. These properties were correlated with the atomic concentration data by Auger electron spectroscopy and x‐ray photoelectron spectroscopy. It has been found that the films of low resistivity had the atomic ratio of O to In of 1.29–1.31.

Characteristics of Flexible ITO Electrodes Grown by Continuous Facing Target Roll-to-Roll Sputtering for Flexible Organic Solar Cells

The preparation and characteristics of flexible indium tin oxide (ITO) electrodes grown on polyethylene terephthalate (PET) substrates are described for use in flexible organic solar cells and prepared using a specially designed facing target roll-to-roll sputtering (FTRS) system. Due to the effective confinement of the high-density plasma between two facing ITO targets, we can deposit the ITO electrode continuously on the PET substrate at a substrate temperature below 50°C without the need of a substrate cooling system, which is used in conventional roll-to-roll sputtering systems. In spite of a low substrate temperature, the FTRS-grown flexible ITO electrode showed a sheet resistance of 42.2 Ω/square, a resistivity of 8.44 × 10 -4 Ω cm, and a transmittance of 85.41% in the 500-550 nm wavelength range with superior flexibility. Furthermore, the flexible organic solar cell fabricated on the FTRS-grown flexible ITO electrode at optimized conditions exhibited a power-conversion efficiency of 2.43%, which is similar to an organic solar cell fabricated on a reference dc sputter-grown ITO electrode. This indicates that the FTRS technique is a promising continuous-sputtering process for preparing flexible ITO electrodes and can substitute for conventional roll-to-roll sputtering systems for mass production of flexible solar cells.

Inverted OLED with Low Resistance IZO–Ag–IZO Top Anode Prepared by Linear FTS System at Room Temperature

We fabricated inverted organic light-emitting diodes (IOLEDs) utilizing a very low resistance indium zinc oxide (IZO)/Ag/IZO multilayer grown by the linear facing target sputtering (LFTS) technique as the top anode layer. By inserting a Ag layer between the IZO layers, it was possible to obtain an IZO-Ag-IZO top anode with a very low resistance of 4.15 Ω/? and a high transparency of 87.04% as well as a high work function of 5.75 eV for the IOLEDs by a room-temperature sputtering process. The IZO-Ag-IZO top anode was deposited on organic layers without inducing any sputtering damage or leakage current in the IOLED due to the effective confinement of the high density plasma between the IZO targets. Furthermore, the current density-voltage-luminescence properties of the IOLED with the LFTS-grown IZO-Ag-IZO top anode were better than those of an IOLED with an amorphous IZO single electrode due to the existence of the Ag layer, which remarkably decreases the resistivity and increases the optical transmittance by its antireflection effect.