Improved characteristics of organic light-emitting devicesby surface modification of nickel-doped indium tin oxide anode

Hsu, Ching-Ming; Wu, Wen-Tuan

doi:10.1063/1.1777416

Cited by 45 publications

(33 citation statements)

References 17 publications

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“…[13][14][15] Because the NiO x layer is a well-known p-type conductor with high work function, it is more desirable for hole injection into the organic layer than ITO.…”

Section: 14mentioning

confidence: 99%

“…For these reasons, several approaches have been employed to increase the work function of ITO, including wet treatment, 7,8 plasma treatment, 9,10 UV ozone treatment, 11 selfassembly monolayer coating treatment, 12 and Ni doping of ITO. 13,14 In particular, several groups have reported that Ni cosputtering with ITO or Ni doping on the surface region of an ITO can potentially enhance hole injection into OLEDs due to the effect of the p-type transparent conductive NiO x layer. [13][14][15] Because the NiO x layer is a well-known p-type conductor with high work function, it is more desirable for hole injection into the organic layer than ITO.…”

mentioning

confidence: 99%

“…13,14 In particular, several groups have reported that Ni cosputtering with ITO or Ni doping on the surface region of an ITO can potentially enhance hole injection into OLEDs due to the effect of the p-type transparent conductive NiO x layer. [13][14][15] Because the NiO x layer is a well-known p-type conductor with high work function, it is more desirable for hole injection into the organic layer than ITO. 16 Similar to ITO anode films, the investigation of Ni doping or cosputtering with indium zinc oxide ͑IZO͒ is therefore necessary to improve the performance of IZO anodes.…”

mentioning

confidence: 99%

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Characteristics of Ni-Doped IZO Layers Grown on IZO Anode for Enhancing Hole Injection in OLEDs

Choi

Jeong

Kim

et al. 2008

J. Electrochem. Soc.

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The preparation and characteristics of a Ni-doped indium zinc oxide ͑NIZO͒ layer were investigated to enhance hole injection in organic light emitting diodes ͑OLEDs͒. A thin NIZO layer with a thickness of 5 nm was cosputtered onto an indium zinc oxide ͑IZO͒ anode using tilted Ni and IZO dual targets dc magnetron sputtering at room temperature in a pure Ar atmosphere. Using 3 W of Ni dc power, we can obtain a NIZO ͑5 nm͒/IZO ͑135 nm͒ double-layer anode with a sheet resistance of 30.04 ⍀/ᮀ and an optical transmittance of 83.8% at a wavelength of 550 nm. In addition, it was found that the work function of the NIZO layer was higher than that of a pure IZO anode due to the presence of a NiO x phase in the NIZO layer. An increase of Ni dc power above 7 W significantly degrades the electrical and optical properties in the NIZO layer. X-ray diffraction examination demonstrated that the NIZO layer consisted of an amorphous structure regardless of the Ni dc deposition power due to low substrate temperature. Furthermore, an OLED fabricated on the NIZO layer exhibited a higher current density, luminance, and efficiency due to improved hole injection by the high work function NIZO. These results indicate that the NIZO/IZO anode scheme is a promising anode material system for enhancing hole injection from the anode into the active layer of OLEDs. Indium tin oxide ͑ITO͒ films deposited on glass substrate have been academically and industrially used as transparent electrodes for organic light emitting diodes ͑OLEDs͒ and flexible OLEDs due to their visible transparency ͑ϳ90%͒ and low resistivity ͑2-4 ϫ 10 −4 ⍀ cm͒. 1-5 High-performance OLEDs and flexible OLEDs require a high-quality ITO anode layer with low resistance, high transparency, chemical stability, and high work function because hole injection and light-emitting properties are critically impacted by the ITO anode layer. 6 Unfortunately, conventional ITO anodes have several drawbacks, such as an imperfect work function alignment with organic materials, chemical instability, high process temperature, and easy deterioration of the ITO target. In particular, the high energy barrier between ITO and the highest occupied molecular orbit of organic materials prevents effective hole injection from the ITO into the organic layer. For these reasons, several approaches have been employed to increase the work function of ITO, including wet treatment, 7,8 plasma treatment, 9,10 UV ozone treatment, 11 selfassembly monolayer coating treatment, 12 and Ni doping of ITO. 13,14In particular, several groups have reported that Ni cosputtering with ITO or Ni doping on the surface region of an ITO can potentially enhance hole injection into OLEDs due to the effect of the p-type transparent conductive NiO x layer. [13][14][15] Because the NiO x layer is a well-known p-type conductor with high work function, it is more desirable for hole injection into the organic layer than ITO.16 Similar to ITO anode films, the investigation of Ni doping or cosputtering with indium zinc oxide ͑IZO͒ is therefor...

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“…[13][14][15] Because the NiO x layer is a well-known p-type conductor with high work function, it is more desirable for hole injection into the organic layer than ITO.…”

Section: 14mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Characteristics of Ni-Doped IZO Layers Grown on IZO Anode for Enhancing Hole Injection in OLEDs

Choi

Jeong

Kim

et al. 2008

J. Electrochem. Soc.

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“…And several kinds of approaches have been proposed to elevate the work function of ITO, such as using metal oxides with high work functions, inserting conducting polymers between ITO and organic material, and depositing metal-doped ITO layers on the ITO surface. [11][12][13] Iridium oxide ͑IrO x ͒ and ruthenium oxide ͑RuO x ͒ are transparent conducting oxides. The work functions of IrO x and RuO x ͑Ͼ5.0 eV͒ are higher than those of ITO ͑ϳ4.7 eV͒.…”

Section: Introductionmentioning

confidence: 99%

Highly efficient organic light-emitting diodes with hole injection layer of transition metal oxides

Kim¹,

Baik²,

Yu³

et al. 2005

Journal of Applied Physics

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We report on the advantage of interlayers using transition-metal oxides, such as iridium oxide (IrOx) and ruthenium oxide (RuOx), between indium tin oxide (ITO) anodes and 4′-bis[N-(1-naphtyl)-N-phenyl-amino]biphenyl (α-NPD) hole transport layers on the electrical and optical properties of organic light-emitting diodes (OLEDs). The operation voltage at a current density of 100mA∕cm2 decreased from 17to11V for OLEDs with 3-nm-thick IrOx interlayers and from 17to14V for OLEDs with 2-nm-thick RuOx ones. The maximum luminance value increased about 50% in OLED using IrOx and 108% in OLED using RuOx. Synchrotron radiation photoelectron spectroscopy results revealed that core levels of Ru 3d and Ir 4f shifted to high binding energies and that the valence band was splitting from metallic Fermi level as the surface of the transition metal was treated with O2 plasma. This provides evidence that the transition-metal surface transformed to a transition-metal oxide. The surface of the transition metal became smoother with the O2 plasma treatment. The thickness was calculated to be 0.4nm for IrOx and 0.6nm for RuOx using x-ray reflectivity measurements. Secondary electron emission spectra showed that the work function increased by 0.6eV for IrOx and by 0.4eV for RuOx. Thus, the transition-metal oxides lowered the potential barrier for hole injection from ITO to α-NPD, reducing the turn-on voltage of OLEDs and increasing the quantum efficiency.

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“…[4][5][6] Several approaches for achieving an elevated ITO work function have been performed to modify its surface chemical states, including surface plasma treatment, the insertion of metal oxides with a high work function between ITO and organic material, and the formation of a metal-doped indium tin oxide layer on an ITO surface. [6][7][8] Rhodium oxide ͑RhO x ͒ is a transparent conducting oxide. The work function of RhO x ͑ϳ5.0 eV͒ is higher than that of ITO ͑ϳ4.7 eV͒.…”

mentioning

confidence: 99%

Rhodium-oxide-coated indium tin oxide for enhancement of hole injection in organic light emitting diodes

Kim

Baik

et al. 2005

Applied Physics Letters

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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.

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Improved characteristics of organic light-emitting devicesby surface modification of nickel-doped indium tin oxide anode

Cited by 45 publications

References 17 publications

Characteristics of Ni-Doped IZO Layers Grown on IZO Anode for Enhancing Hole Injection in OLEDs

Characteristics of Ni-Doped IZO Layers Grown on IZO Anode for Enhancing Hole Injection in OLEDs

Highly efficient organic light-emitting diodes with hole injection layer of transition metal oxides

Rhodium-oxide-coated indium tin oxide for enhancement of hole injection in organic light emitting diodes

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