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The authors report the enhancement of hole injection using an indium tin oxide ͑ITO͒ anode covered with ultraviolet ͑UV͒ ozone-treated Ag nanodots for fac tris ͑2-phenylpyridine͒ iridium Ir͑ppy͒ 3-doped phosphorescent organic light-emitting diodes ͑OLEDs͒. 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 Ag 2 O nanodots with high work function and high transparency. Phosphorescent OLEDs fabricated on the Ag 2 O 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 Ag 2 O nanodots by UV-ozone treatment, the decrease of the energy barrier height led to the enhancement of hole injection in the phosphorescent OLEDs.

A facing target sputtering ͑FTS͒ system with a configuration of vertically parallel facing Al targets and a substrate holder perpendicular to the Al target plane was designed for direct sputtering of Al cathode on organic layers at a low substrate temperature. The linear FTS system has a linear twin target gun with ladder-type magnet arrays for more effective and uniform confinement of high-density plasma. Due to more effective confinement of high-density plasma and a perpendicularly placed substrate position, we were able to deposit an Al cathode layer directly on an organic layer at a low temperature of ϳ50°C without an additional substrate cooling system. It was found that organic light-emitting diodes ͑OLEDs͒ with linear FTS-grown Al cathodes have a lower leakage current density than that of OLEDs with dc-sputtered Al cathodes. The leakage current of OLEDs with linear FTS-grown Al cathodes is similar to reference OLEDs with Al cathodes grown by thermal evaporation. The low leakage current density at reverse and forward bias demonstrates that there is no plasma damage effect caused by the bombardment of energetic particles. This indicates that the FTS system with ladder-type magnet array could be effective in direct Al cathode sputtering on OLEDs or organic photovoltaics.Organic-material-based optoelectronic devices, such as organic light emitting diodes ͑OLEDs͒, organic photovoltaics ͑OPVs͒, organic thin-film transistors, and organic memories have attracted considerable attention because of their low cost, flexibility, and easy processability. 1-3 To fabricate high-performance organic-based devices, it is very important to prepare a high-quality metal cathode layer on organic layers. 4 In particular, OLEDs and OPVs require a high-quality metal cathode ͑Al, Al-Li, Mg-Ag, Ag͒ with low work function, low resistance, and chemical stability. 1,3,5-8 Until now, Al cathodes have been commonly employed in OLEDs or OPVs as a cathode material due to high electron injection efficiency and chemical stability. However, the difficulty of Al cathode deposition using thermal evaporation is one of the critical problems in the fabrication of OLEDs and OPVs. This is due to serious undesirable reactions of Al with the ceramic crucible and the creeping up of Al on the ceramic crucible wall, low material usage, unstable rate control, and difficulty of achieving a large-area deposition due to point-type Al source geometry. To solve such drawbacks of Al thermal evaporation, the sputtering technique has been considered as an alternative Al cathode deposition method. 9,10 Since Suzuki et al. reported the sputtered Al and Mg-Ag cathode on OLEDs, there have been many efforts to apply the sputtering method to OLEDs. 9-12 However, it is not easy to deposit metal cathodes on organic layers without plasma damage due to the high sensitivity of organic materials to radiation and the bombardment of energetic particles ejected from plasma. As a plasma-damage-free sputtering technique, facing target sputtering ͑FTS͒ has been regarded as the most...

Transparent and low resistance amorphous ZnO-doped In 2 O 3 ͑IZO͒ anode films were grown by radio-frequency ͑rf͒ sputtering on an organic passivated polyethersulfone ͑PES͒ substrate for use in flexible organic light-emitting diodes ͑OLEDs͒. Under optimized growth conditions, a sheet resistance of 15.2 ⍀/ᮀ, average transmittance above 89% in the green range, and a root mean square roughness of 0.375 nm were obtained, even for the IZO anode film grown in a pure Ar ambient without the addition of oxygen as a reactive gas. All of the IZO anode films had an amorphous structure regardless of the rf power and the working pressure due to the low substrate temperature of 50°C and the structural stability of the amorphous IZO films. In addition, an X-ray photoelectron spectroscopy depth profile obtained for the IZO/PES showed no obvious evidence of interfacial reactions between the IZO anode and the PES substrate, except for some indiffusion of oxygen atoms from the IZO anode. Furthermore, the current-voltageluminance of the flexible OLEDs fabricated on IZO anode was found to be critically dependent on the sheet resistance of the IZO anode.

The preparation and characteristics of a transparent conducting indium zinc tin oxide ͑IZTO͒ anode for highly efficient phosphorescent organic light emitting diodes ͑OLEDs͒ is described. The resistivity and transmittance of the IZTO anode are comparable to reference In 2 O 3 ͑ITO͒ anode films even though it was prepared at room temperature. In addition, the work function of the ozone-treated amorphous IZTO anode ͑5.12 ± 0.02 eV͒ is much higher than that of ozone-treated reference ITO anodes ͑4.94 ± 0.02 eV͒. The current-voltage-luminance characteristics and efficiencies of OLEDs prepared on the IZTO anode are critically dependent on the sheet resistance of the IZTO anode. Furthermore, both the quantum efficiency and power efficiency of the OLED fabricated on the amorphous IZTO anode are much higher than those of an OLED with the reference ITO anode due to the higher work function of the IZTO anode than those of conventional ITO anode. This indicates that IZTO is an alternative material for conventional ITO anodes used in OLEDs and flexible displays.Organic light emitting diodes ͑OLEDs͒ are of considerable importance for their potential as a new generation of flat panel displays and flexible displays due to their high peak brightness, high dark room contrast, low power consumption, low-cost, super viewing ability, and fast response time. 1,2 In order to obtain highperformance OLEDs and flexible OLEDs, it is very important to develop a high-quality anode layer with low resistance, high transparency, chemical stability, and a high work function. 1,2 Although Sn-doped In 2 O 3 ͑ITO͒ has been commonly used in OLEDs and flexible OLEDs as an anode material due to high conductivity and transmittance in visible range, the conventional ITO anode has several problems, such as an imperfect work function alignment, chemical instability, high process temperature, and easy deterioration of the ITO target. 3,4 Recently, both ternary oxide and multicomponent oxides, such as Al-Zn-O ͑AZO͒, Ga-Zn-O ͑GZO͒, Zr-Zn-O ͑ZZO͒, In-Ga-O ͑IGO͒, In-Zn-O ͑IZO͒, In-Ga-Sn-O ͑IGTO͒, and Zn-In-Sn-O ͑IZTO͒ have gained much attention as promising anode materials for OLED and flexible OLEDs. 3,5-7Among the various multicomponent-TCO materials, IZTO films have recently been recognized as attractive anode materials in OLEDs and flexible OLEDs due to their high work function, good conductivity, high-transparency, and low-deposition temperature. 3 Phillips et al. reported that Zn x In 2−y SnyO 3+x−␦ film grown by pulsed laser deposition and sputtering has high conductivity and transmittance within ranges typically reported for ITO films. 8 In addition, Ambrosini et al., investigating zinc doping in cosubstituted In 2−2x Sn x Zn x O 3−␦ bulk pellet, found that the solubility of ZnO and SnO 2 in In 2 O 3 can be greatly increased up to x = 0.4 by codoping with equal amounts of Zn and Sn in the In 2 O 3 . 9 Mark et al., in an investigation of the high work function transparent conducting oxide as an anode for an OLED, reported that an IZTO film has a higher ...