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In this work, we report top emission white OLED (TE-WOLED) device for an application to large sized and high resolution OLED TV. Like as bottom emission device, we adopted 3 stack WOLED consisting of two blue and one yellow green (YG) light-emitting units with a reflective metal as the bottom anode and a transparent compound as the top cathode. By using an optical simulation, we designed the device structure and found optimum positions for EML with consideration of viewing angle property. As a result, we demonstrate top emission white OLED comparable to bottom emission OLED, regarding efficiency, operating voltage and viewing angle.

Ultra-high definition (UHD) curved organic light-emitting diode (OLED) TV requires advanced technologies to realize mass production. White, red, green, and blue (WRGB) OLED TV based on stripe WRGB sub-pixel structure has distinct advantages in luminance of white, faster response time, wider viewing angle, and potential higher resolution. In this paper, we will introduce technological progress for commercializing large-sized and UHD curved OLED TV. Those technologies including oxide thin film transistors, white OLEDs, compensation circuit, and solid phase encapsulation enable panel size scalability as well as mass production with lifetime reliability.

Large-sized OLED displays require advanced technologies to realize mass production. The competitiveness of OLED TV comes from the combination of oxide TFT and WRGB OLED technology. Those technologies including image quality of OLED TV, oxide TFT, WOLEDs, and solid phase encapsulation enable panel size scalability as well as mass production with lifetime reliability. We will introduce technological progress for commercializing large-sized OLED TV.

The 5.98 inch-sized World's first flexible OLED display has been developed and launched mass production on smartphone with extremely light, thin and curved shape, successfully. We have employed ELA-TFT on PI backplane, Face-sealing encapsulation, Laser-assisted glass release and flexible back-plate lamination process. These technologies enable panel reliability as well as mass production with inherent flexible display characteristics. For commercializing flexible OLED, technical barriers and challenges on TFT device, panel design and various process technologies including LG Display's recent experience will be presented in this paper.

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...

White organic light-emitting diode (WOLED) with color filter adopting dual-plate OLED display (DOD) structure is proposed. In order to prevent outgassing from color filter and overcoat, the SiNx passivation film was deposited on the overcoat film. This structure does not show any defects after it has been kept over 500 hours of storage tests at 90 degC . By fabricating 1 stacked WOLED consisting of fluorescent blue layer/ phosphorescent red:green layer, luminance efficiency of 20 cd/A with CIEx = 0.29, CIEy = 0.37 was achieved.

We fabricated 2-stack white organic light-emitting diode (WOLED) structure with luminance efficiency of 27.4 cd/A and color point of (0.32, 0.29) where one unit device emitted blue color and the other emitted red and green colors. Comparing with other configurations possible for 2-stack WOLED, it was found that our structure had merits of higher color gamut and lower power consumption, in spite of low luminance efficiency. In our 2-stack structure, we found that the blue efficiency which determines the power consumption of panel was strongly dependent on the position of the blue emitting layer. Based on an optical simulation and a viewing-angle analysis, we proved that the change of the luminance of blue color came from the microcavity effect depending on the distances between anode and cathode and between blue emitting layer and cathode.

A high efficiency pure white phosphorescent organic light-emitting diode was developed by combining a deep blue emitting phosphorescent dopant material with red/green phosphorescent emitting materials. A simple stack structure of blue/red:green was used and tris((3,5-difluoro-4-cyanophenyl)pyridine) iridium was used as a deep blue emitting phosphorescent dopant. A pure white emission with a color coordinate of (0.29, 0.31) and a very high current efficiency of 28 cd/A was obtained after managing the device architecture of the all phosphorescent white devices.

The preparation and characteristics of indium tin oxide (ITO) electrodes grown using a specially designed linear facing target sputtering (LFTS) system with a ladder type magnet arrangement for organic light emitting diodes (OLED) are described. It was found that the electrical and optical properties of the ITO electrode were critically dependent on the Ar/O 2 flow ratio, while its structural and surface properties remained fairly constant regardless of the Ar/O 2 flow ratio, due to the low substrate temperature during the plasma damage-free sputtering. Under the optimized conditions, we obtained an ITO electrode with the lowest sheet resistance of 39.4 Ω/sq and high transmittance of 90.1% (550 nm wavelength) at room temperature. This suggests that LFTS is a promising low temperature and plasma damage free sputtering technology for preparing high-quality ITO electrodes for OLEDs and flexible OLEDs at room temperature.

Thin silver film is widely used as the cathode in organic light-emitting diode displays and it is generally fabricated using the thermal evaporation method. But during the evaporation process, there is an inevitable outgassing problem and this creates high viscosity bubbles in melted silver. When the bubbles break, the high energy released scatters silver droplets which damage the silver surface. In this study, we were able to decrease the number of droplets from 6,171 to 278 with a degassing process of 400 °C for 6 h before proceeding with a thermal evaporation process.

Novel platinum complex of porphyrin with methyl and cyclohexyl substituents, PtMECHP, was designed and synthesized for use as a red phosphorescent material. PtMECHP was employed as an emission dopant in the OLED and the elctro-optical characteristics were investigated. The OLED was fabricated by vacuum deposition, and the layer-structure of device was ITO/NPD/PtMECHP(10%) in CBP/BCP/Alq/LiF/Al to exhibit brightness of 53 cd/m2 at 11 mA/cm2 and the external quantum efficiency of 1.2% at the same current density. The maximum EL band was detected at 650 nm with red phosphorescence.

Novel red phosphorescent iridium complex with two phenyl-isoquinoline ligands and one 2-acetyl-cyclopentanone ligand (IR-PIQCP) was designed and synthesized. The electroluminescent (EL) characteristics of IR-PIQCP were evaluated in the EL device. The three kinds of EL devices were fabricated by the vacuum deposition method, and the layer-structures of the devices were ITO/NPD/IR-PIQCP (5%), IR-PIQCP (10%) or IR-BTPAC (10%) in CBP/Balq/Alq/LiF/Al. Emission characteristics of the IR-PIQCP (5%) and IR-PIQCP (10%) devices were about 570 cd/m2 and 550 cd/m2 at 11 mA/cm2 at the same current density respectively. The EL spectra of the IR-PIQCP (5%) and IR-PIQCP (10%) devices were detected at about 627 nm and 629 nm as the maximum peak with red phosphorescence.

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.

Novel green phosphorescent materials, IR-PPA1, IR-PPA2 and IR-PPA3 were synthesized as emission dopants for electroluminescent(EL)devices. Four kinds of devices were fabricated and the structures of devices were ITO/NPD/IR-PPA1(6%), IR-PPA2(6%), IR-PPA3(6%)or IR-PPY(6%)in CBP/BCP/Alq/LiF/Al, where IR-PPY was used as a reference material for comparison. Novel phosphorescent materials, IR-PPA1, IR-PPA2 and IR-PPA3 represented the luminances of 3930 cd/m2, 3220 cd/m2and 2620 cd/m2, and their external quantum efficiencies, about 9.4%, 7.8%and 6.4%in 11 mA/cm2of current density in the EL devices, respectively. The maximum of EL spectra of novel emission dopants were detected at 532 nm in the IR-PPA1 device, and 525 nm in the IR-PPA2 device and 530 nm in the IR-PPA3 device.

We report a 55-inch OLED TV employing white organic light emitting device (WOLED) and oxide TFT. We fabricated the hybrid tandem structure comprising a phosphorescent R/G stack and a fluorescent blue stack to achieve high current efficiency of 90cd/A at 1,000 nit and white color (0.327, 0.344). 55-inch OLED TV was adjusted to cool white color of (0.285, 0.294). We applied a color layer for large color gamut (118% ATSC ratio) and deep blue expression (0.142, 0.054). We also improved 3 kinds of color shift over viewing angle, aging and gray level.

TCO (transparent conductive oxide) thin films such as ITO (indium tin oxide) have important roles in fabrication of OLED (organic light emitting diode) displays. Although ITO is the most widely used transparent conductor in the field of FPD (flat panel display) industry, there are some unique requirements from the viewpoint of OLED, which is different from other display devices such as LCD (liquid crystal display) and PDP (plasma display panel). Especially surface roughness and work function are very important to enhance the stability and efficiency of OLED. Because all functional organic layers which act as injection, transportation and emission layers are deposited on ITO, surface morphology of ITO is directly transferred to them and uneven interface is not desirable for the efficiency and stability of OLED. On the other hand, there are several different terminologies—Ra (average roughness), Rr.m.s. (root-mean-square roughness) and Rpv (peak to valley roughness)—which are used to interpret the surface roughness, are now all used altogether. In this work, we tried to define which parameter is the most suitable to characterize ITO for OLED and to explain the relationship between surface and I–V characteristics of OLED. To characterize the effect of surface morphology of the ITO electrode, light emitting diodes were fabricated using various types of ITO films which have different surface morphology and their dynamic characteristics were compared.

Hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) which have tungsten shield layer for AMOLED were fabricated. E-beam evaporation is useful method to prepare cathode layer above organic layers with high throughput and no damage to the organic layers but TFTs are damaged by X-ray radiation generated during the e-beam process. When the thickness of the tungsten layer was increased to 2000 A, it was found that the characteristics of TFTs, such as threshold voltage, field effect mobility and sub-threshold slope, were slightly varied by X-ray radiation.

Novel red phosphorescent compound (IR-PIQC-1), iridium complex with two phenyl-isoquinoline ligands and one 2-acetyl-1,3-cyclohexanedione ligand was designed and synthesized. The electroluminescent (EL) characteristics of IR-PIQC-1 in the EL device were evaluated. The thin layers of EL devices were fabricated by the vacuum deposition method, and the layer-structures of the devices were ITO/NPD/IR-PIQC-1 or IR-BTPAC (10%) in CBP/Balq/Alq/LiF/Al. Brightness of the IR-PIQC-1 device was 574 cd/m2 at 11 mA/cm2, and the external quantum efficiency was estimated as 5.28% at the same current density. The EL spectrum of the IR-PIQC-1 device was detected at about 620 nm as the maximum peak with red phosphorescence.

World’s first commercialized 55-inch WRGB OLED TV has been developed and launched recently. Large-sized OLED displays require novel technologies to realize mass production. We will introduce commercialized 55-inch WRGB OLED TV and its novel technologies including oxide TFT, WOLED, solid phase encapsulation, and compensation technologies.

Novel red electroluminescent (EL) materials, IAP-1 and IAP-2, were designed and synthesized for an emission layer in EL devices. Three types of devices with IAP-1, IAP-2 and DCJTB as dopants of emission layers were fabricated, where DCJTB was adopted as a red dopant for reference. The structures of three devices were ITO/CuPc/TPD/0.5% IAP-1 in Alq 3 /Alq 3 /Li 2 O/Al as an IAP-1 device, ITO/CuPc/TPD/0.5% IAP-2 in Alq 3 /Alq 3 /Li 2 O/Al as an IAP-2 device and ITO/CuPc/TPD/0.5% DCJTB in Alq 3 /Alq 3 /Li 2 O/Al as a DCJTB device. The IAP-1 and IAP-2 devices showed about two times higher quantum efficiency than the DCJTB device. The EL spectra of the IAP-1 and IAP-2 devices had the maximum peak intensities at 635 and 615 nm, respectively.

The insertion of LiF for an interlayer material between the Al cathode and tris-(8-hydroxyquinoline) aluminum (Alq3) in the organic light-emitting diodes (OLEDs) provides an improved device performance. The highly occupied molecular orbital (HOMO) level lowering in the Alq3 layer induced by a low-coverage LiF deposition results in the reduction of electron injection barrier height. We investigated the electronic structure of the interface between the ultrathin LiF and the Alq3 layer, using synchrotron x-ray photoelectron emission spectroscopy. The results revealed that the major origin of the HOMO level lowering is not the chemical bonding of dissociated fluorine in the Alq3 layer but the band bending caused by charge redistribution driven by work function difference between LiF and Alq3 layer.

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.

Surface roughness of ITO (Indium Tin Oxide) was measured by AFM (Atomic Force Microscope) and the existence of spikes was verified. Then OLED (Organic Light Emitting Diode) devices made from those substrates were fabricated and their electrical properties were measured with an I-V measurement system. There is considerable difference in the reverse leakage current of OLEDs depending on the surface roughness of the substrate. We observed a good correlation of reverse leakage current with Rpv (Peak-to-Valley roughness), but the correlations between reverse leakage current and Ra (Average roughness) and Rrms (Root-Mean-Square roughness) are not as good.

— A 15-in. HD panel employing two-stacked WOLEDs and color filters for which the color gamut can be as high as 101.2% (CIE1976) and the power consumption is 5.22 W. The WOLEDs exhibit a current efficiency of 61.3 cd/A and a power efficiency of 30 lm/W at 1000 nits and their CIE coordinate is (0.340, 0.334). A 15-in. RGBW panel was investigated to verify the electrical and optical performance compared to that of a 15-in. RGB TV made by using FMM technology. The characteristics of the 15-in. RGBW panel are comparable to those of the 15-in. RGB panel. Color filters combined with WOLEDs is a possible patterning technology for large-sized OLED TV, which surpasses the limits of fine-metal-mask technology.

We have developed a twostacked white OLED based on bottomemission structure for largesized display. It consists of one unit emitting fluorescent blue and the other unit emitting phosphorescent yellow twodopant of red and green in a host layer. In order to improve the performance of the WOLED, we adopted new noncabazole compound as a hole transporting layer with high triplet energy level and akali—metal doped charge generation layer. In addition, we employed new greenish yellow dopant instead of previous green dopant to enhance the lifetime of the phosphorescent stack. The resulting device exhibits 61.3 cd/A of current efficiency, 30 lm/W of power efficiency, and 6.4 V of driving voltage of at 1000 nit where its CIE coordinate is 0.340, 0.334. Halflifetime T50 of the device is estimated more than 130,000 hrs at 1000 nit. We also fabricated 15inch HD panel employing the twostacked WOLED and color filter.

We have studied an efficient interconnecting layer (TR-E314:Li/LGC101:NPB), in stacked organic light-emitting diodes (OLEDs). The interconnecting layer is applied to stacked blue OLEDs that have two emission units. The efficiency of this OLED is twice that of the single-unit device. The current, power efficiency, and operating voltage of the blue OLED reached 14.6 cd/A, 7.3 lm/W, and 6.3 V, respectively, at 10 mA/cm2. The Commission Internationale d'Eclairage (CIE) coordinates of the stacked OLED device are (0.128, 0.228). The 20% decay lifetime (t0.8) of the stacked OLED (366 h) is 4.4 times that of the single-unit OLED.

In this letter, we analyze the device performance of organic light-emitting diodes (OLEDs) with a lithium-quinolate (Liq)-doped electron transport layer (ETL). When the ETL:Liq doping ratio is 1:3, the luminous efficiency of the OLED is 7.1 cd/A; that of an OLED with a nondoped ETL is 5.3 cd/A. The corresponding OLED lifetime is improved by threefold that with a nondoped ETL, owing to the improved hole-electron charge balance and electrical stability of the Liq-doped ETL film. Additionally, when the Liq-doped device was combined with a Mg/Al cathode, the OLED produced had a longer lifetime than the other tested devices.

Corrigendum to “Criteria for ITO (indium–tin–oxide) thin film as the bottom electrode of an organic light emitting diode” [Thin Solid Films 411 (2002) 12–16] Yoon-Heung Tak , Ki-Beom Kim ⁎, Hyoung-Guen Park , Kwang-Ho Lee , Jong-Lam Lee b a OEL Development Group, PDP Division, LG Electronics 191-1 Kongdandong, Kumi, 730-030, South Korea b Department of Material Science and Engineering, POSTECH San 31 Hyojadong, Pohang, 790-784, South Korea

— An improved AMOLED with an a-Si TFT backplane based on a unique structure is reported. The new structure is refered to as a dual-plate OLED display (DOD). While a top-emission OLED array is directly fabricated on a TFT backplane, the DOD consists of an upper OLED substrate and a lower TFT substrate, which are independently fabricated. Because the OLED substrate, which is fabricated through the process flow of bottom emission, is attached to the TFT substrate, the light is emitted in the opposite direction to the TFT backplane. The DOD enables the design of large-sized TFTs and a complicated pixel circuit. It can also not only achieve higher uniformity in luminance in large-sized displays due to the low electrical resistance of the common electrode, but also wider viewing angles.

We report an improved bottom-emission two-stacked white OLED structure consisting of one unit emitting fluorescent blue light and the other unit emitting phosphorescent yellow in one-host and two-dopant (R+G) system. By searching EL condition optimizing both phosphorescent green and red dopants within just one light-emitting layer, we can get WOLEDs suitable for a display application with very high current and power efficiencies, and excellent color characteristics. Our device exhibits high external quantum efficiency of 28.8%, current efficiency of 56.5 cd/A, and power efficiency of 30 lm/W at 5.9 V and 1000 nit where color point is (0.368, 0.385) in x-y color space (CIE 1931). Half-lifetime (LT50) of the device at 1000 nit is estimated more than 31,000 hrs and color variation by aging is suppressed within less than 0.02 in u'-v'color space (CIE 1976). Color filter developed for our WOLED enables color gamut to become wider than the 100% NTSC in uniform color space (u', v').

We report the correlation between charge injection and charge balance using lithium fluoride/aluminum (LiF/Al) cathode and iridium oxide (IrO x )-coated indium tin oxide (ITO) anode in organic light emitting diodes (OLEDs). The turn-on voltage decreased from 6.7 to 1.0 V and luminous efficiency at 80 mA/cm 2 increased from 1.24 to 4.60 cd/A due to the presence of LiF and the high work function of IrO x . When IrC x was used in the anode region, the luminous efficiency increment rate decreased from 40% in Al cathode OLED to 7% in LiF/Al cathode OLED. The value of the carrier density suggested that the majority carrier changed from electrons in ITO-LiF/Al OLEDs to holes in ITO/IrC x -LiF/Al OLEDs, reducing the rate of increase. Therefore, it has been considered that charge injection should be increased and balanced in order to maximize the luminous efficiency.

We report new DOD structure employing WOLED with color filters patterning RGBW sub-pixels. The DOD structure consists of the top plate on which organic layer was evaporated and the bottom plate involving TFT arrays. for white OLED, the top plate contains reformulated RGBW color filters and an overcoat layer. The EL efficiency of one-stacked WOLED is 18.7 cd/A with CIE x, y coordinates of (0.31, 0.35) at 4.3 mA/cm2. By combining WOLED and the DOD structure using a-Si backplane, we obtained the high aperture ratio up to 67% in the panel having the same pixel size for 32 ″ Full HD, and use of color filters developed for our WOLED enables color gamut to become wider than the 100% NTSC in uniform color space (u',v').

a-Si:H TFT backplane based AMOLED with a real time brightness compensation circuit is presented. The brightness of AMOLED is automatically adjusted by the thermal sensor and temperature compensation system with feedback algorithm. By using this compensation circuit, the brightness differences over the temperature range −20 °C and 60 °C is reduced by 550cd/m2 to 30cd/m2.

We report the enhancement of the electroluminescent property of organic light-emitting diodes (OLEDs) using MoO x as a hole injection layer between indium tin oxide (ITO) anodes and 4,4'-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (α-NPD). The operation voltage for 100 mA/cm 2 of OLEDs with a 10 A thick MoO x layer decreased from 24.5 to 14.7 V, and the luminescence value at 190 mA/cm 2 increased from 1280 to 9750 cd/m 2 . α-NPD was deposited in situ on O 2 -plasma-treated ITO (O 2 -ITO) anodes and O 2 -ITO anodes coated with an O 2 -plasma-treated MoO, layer (O 2 -MoO x ,), and their interface dipole energies were quantitatively determined using synchrotron radiation photoemission spectroscopy. Secondary electron emission spectra after the deposition of α-NPD on anodes revealed that the work function of O 2 -MoO x , is 0.55 eV higher than that of O 2 -ITO. The corresponding interface dipole energies were -0.20 eV for O 2 -ITO and -0.50 eV for O 2 -MoO x . The hole injection barrier at the interface was reduced from 1.15 to 0.85 eV by the deposition of MoO x , resulting in an enhancement of the electroluminescence property of OLEDs.

We report the improved AMOLED with a-Si TFT backplane based on our unique structure. Our new structure use the encapsulation glass as a substrate for OLED which enable us to achieve the high aperture ratio, large TFT area, high luminescence uniformity, and low anode resistance.

The authors report electroluminescence degradation in organic light emitting diode operated at a high current density of 500mA∕cm2 under nitrogen ambient. The turn-on voltage increased from 6to10V, and a number of dark spots were produced when the device was operated for 420min. Microscope image showed that dark spots are related to many protrusions and hollows formed on Al electrode. X-ray diffraction and scanning photoemission microscope spectra indicate that the Joule heat from high electric field induced the crystallization of 4′-bis[N-(1-naphtyl)-N-phenyl-amino]biphenyl, forming dark spots via peeling off of the Al cathode.

We report the enhancement of electron injection using an Al-Mg alloy cathode in organic light emitting diodes (OLEDs). The luminescence value at 15 V drastically increased from 800 to 5800 cd/m 2 as the Al cathode was replaced by an Al-Mg alloy with a 1:1 ratio of Al to Mg in weight percent. Synchrotron radiation photoelectron spectroscopy results showed that the work function of the Al-Mg alloy is lower by 0.2 eV than that of Al. Thus, the energy barrier for electron injection was lowered, reducing the turn-on voltage and increasing the quantum efficiency of OLEDs.

The authors report the enhancement of hole injection using an RhOx layer between indium tin oxide anodes and 4,4′-bis[N-(1-naphtyl)-N-phenyl-amino]biphenyl in organic light-emitting diodes (OLEDs). The operation voltage of OLEDs at 700cd∕m2 decreased from 13 to 10 V as the Rh layer changed to RhOx by surface treatment using O2 plasma. Synchrotron radiation photoelectron spectroscopy results showed that the work function increased by 0.2 eV as the Rh layer transformed into RhOx. Thus, the hole injection energy barrier was lowered, reducing the turn-on voltage and increasing the quantum efficiency of OLEDs.

We report the enhancement of hole injection using an IrOx layer between indium tin oxide anodes and 4,4’-bis[N-(1-naphtyl)-N-phenyl-amino]biphenyl in organic light-emitting diodes (OLEDs). The turn-on voltage of OLEDs decreased from 7V to 4V and the maximum luminescence value increased from 1200cd∕m2 to 1800cd∕m2 as the Ir layer changed to IrOx by surface treatment using O2 plasma. Synchrotron radiation photoelectron spectroscopy results showed that the work function increased by 0.6eV as the Ir layer transformed into IrOx. Thus, the hole injection energy barrier was lowered, reducing the turn-on voltage and increasing the quantum efficiency of OLEDs.

We investigated the remote oxygen and hydrogen plasma cleaning of indium-tin oxide and its surface electronic properties. Samples cleaned by hydrogen plasma after oxygen plasma cleaning showed the complete absence of surface contaminants while samples cleaned by only hydrogen or oxygen plasma showed some residual contaminants. Work function is mainly affected by oxygen plasma treatments while sheet resistance is more closely related to the removal of surface carbon contaminants. This study revealed that surface dipoles due to the O- ions are believed to have a more significant contribution to the change in work function than the reduction of Sn4+.

We report the enhancement of hole injection using AgOx layer between Ag anode and 4,4′-bis[N-(1-naphtyl)-N-phenyl-amino]biphenyl in top-emitting organic light-emitting diode (OLED). The turn-on voltage of OLEDs decreased from 17 to 7V as Ag changed to AgOx by the surface treatment using O2 plasma. Synchrotron radiation photoelectron spectroscopy results showed that the work function increased about 0.4eV by the O2 plasma treatment. This led to the decrease of the energy barrier for hole injection, reducing the turn-on voltage of OLEDs.

We report the change of surface electronic structure of indium tin oxide (ITO) as a function of UV-ozone treatment time. The voltage at the current of 100 mA/cm2 is lowered as a function of UV-ozone treatment time. It was found that the atomic concentration of carbon decreased, and that of oxygen increased. This leads to the increase of ITO work function via the reduction of turn-on voltage.