Improving the viewing angle properties of microcavity OLEDs by using dispersive gratings

Choy, Wallace C. H.; Ho, Ching-Yen

doi:10.1364/oe.15.013288

Cited by 39 publications

(27 citation statements)

References 21 publications

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“…Together with the J-V results of the ITO/Au/V 2 O 5 OLED, as discussed previously, the higher current efficiency of ITO/Au/V 2 O 5 OLED than ITO/V 2 O 5 OLED is attributed to the better charge balance [21]. Moreover, the improved current efficiency is not likely due to the microcavity effect [22] in the device with ITO/Au/V 2 O 5 anode because there is no change in electroluminescence spectrum (not shown in this brief). The reduction of operation voltage can be explained by lowering the barrier of hole injection from anode to HTL.…”

supporting

confidence: 76%

Indium Tin Oxide Modified by Au and Vanadium Pentoxide as an Efficient Anode for Organic Light-Emitting Devices

Zhang

Choy²

2008

IEEE Trans. Electron Devices

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CONVENTIONAL bottom emitting organic light-emitting devices (OLEDs) commonly use conductive indium tin oxide (ITO) as anode because of its high conductivity, transparency, and work function. However, the surface of ITO glass is chemically and physically ill defined, which will degrade the performance as the hole-injecting electrode in OLEDs. Over the past years, many methods were used to treat the surface of ITO [1]- [5], such as ultraviolet-ozone cleaning and oxygen plasma exposure, in order to enhance hole injection [1], [2]. These treatments were effective in removing residual surface contaminants and increasing oxygen content at ITO surface, resulting in the increase of work function to minimize interfacial charge injection barriers.Moreover, the incorporation of injection enhancing interlayer at electrode-organic interfaces has been used as one alternative route to control carrier injection [6] In this brief, we use V 2 O 5 coating on transparent thin Au film as a composite hole-injection layer on ITO anode for bottom emitting OLEDs. The characteristics of bottom emitting OLEDs with the composite anodes of ITO-Au-V 2 O 5 are described. A thin oxide layer V 2 O 5 is used to modify the surface of Au for enhancing the hole injection from Au by the increase of work function to 5.3 eV and thus sequentially improves emission efficiency. The effects of V 2 O 5 layer on the enhancement of electrical properties of the bottom emitting OLEDs are discussed. Ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS, respectively) analysis indicate that the higher work function of ITO/Au/V 2 O 5 (5.3 eV) than ITO/Au (5.0 eV) anode is due to Au surface band bending. Thus, the barrier for hole injection from ITO through Au/V 2 O 5 to the hole transport layer (HTL) is decreased. Our results show that the performance of OLEDs with V 2 O 5 layer is greatly improved compared with the case of only Au layer on the ITO. Interestingly, it is also better than the ITO anode modified by V 2 O 5 device.All devices were fabricated on ITO coated glass with a sheet resistance of 10 Ω/ , and thermally deposited LiF/Al was used as cathode. ITO substrate was cleaned and treated by O 2 plasma. The deposition was carried out at a pressure of less than 3 × 10 −4 Pa without any vacuum break. The organics and metal oxide were evaporated at the rate in a range of 0.3-0.4 nm/s. The Au metals were evaporated at the rate of ∼0.1 nm/s prior to the oxide and organic layer deposition. Al metal was evaporated at the rate of 0.3∼0.5 nm/s. The devices have an emissive area of 3.57 mm

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confidence: 76%

Indium Tin Oxide Modified by Au and Vanadium Pentoxide as an Efficient Anode for Organic Light-Emitting Devices

Zhang

Choy²

2008

IEEE Trans. Electron Devices

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“…This occurs because the resonant cavity design can be chosen to maintain a larger viewing angle than that with the standard ITO devices. Unlike micro-cavity OLEDs which suffer from significant colour shifts with viewing angle, 17 our resonant cavity which is formed between the silver in the anode and the aluminium cathode layer (separated by 80-140 nm active layer), if designed carefully does not suffer as severely from the same problem. This was verified with optical modelling of the device stacks and then confirmed with experimental data.…”

Section: Angular Spectral Response a Datamentioning

confidence: 99%

AZO/Ag/AZO anode for resonant cavity red, blue, and yellow organic light emitting diodes

Gentle

Yambem

Burn

et al. 2016

Journal of Applied Physics

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Indium tin oxide (ITO) is the transparent electrode of choice for organic light-emitting diodes (OLEDs). Replacing ITO for cost and performance reasons is a major drive across optoelectronics. In this work, we show that changing the transparent electrode on red, blue, and yellow OLEDs from ITO to a multilayer buffered aluminium zinc oxide/silver/aluminium zinc oxide (AZO/Ag/AZO) substantially enhances total output intensity, with better control of colour, its constancy, and intensity over the full exit hemisphere. The thin Ag containing layer induces a resonant cavity optical response of the complete device. This is tuned to the emission spectra of the emissive material while minimizing internally trapped light. A complete set of spectral intensity data is presented across the full exit hemisphere for each electrode type and each OLED colour. Emission zone modelling of output spectra at a wide range of exit angles to the normal was in excellent agreement with the experimental data and hence could, in principle, be used to check and adjust production settings. These multilayer transparent electrodes show significant potential for both eliminating indium from OLEDs and spectrally shaping the emission.

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“…The microcavity effect causes the blue shift of viewing angle, and this phenomenon not only results in a shorter wavelength but also causes the brightness to vary at different viewing angles 3 for the full color display. In this study, we discuss the blue shift of viewing angle in the top-emitting organic light-emitting devices.…”

Section: Introductionmentioning

confidence: 99%

Improvement in viewing angle properties of top-emitting organic light-emitting devices

et al. 2011

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The blue shift of viewing angle in the top-emitting organic light-emitting devices is discussed in this study. For the single-mode cavity, the device of anode metal/ m-MTDATA (40 nm)/ α-NPD (10 nm)/ Alq 3 (47.6 nm)/ LiF (1 nm)/ Ag (20 nm) with the metal phase difference of 1.30 π has the minimum blue shift of viewing angle. For the double-mode cavity, the recombination area must be away from the cathode for the device with better performance. However, the double-mode cavity with only one recombination area still has worse FWHM and gets more serious the blue shift of viewing angle than the single-mode cavity. Therefore, the double-mode cavity with a recombination area at each antinode is performed, and the results prove that the blue shift of viewing angle and the FWHM are improved. Finally, we replace the emission layer with Alq 3 :DCM (0.01%) and adjust the main peak wavelength in the double-mode cavity by adjusting the thicknesses of the cavity. The results show that the FWHM and the blue shift of viewing angle obtain further improvement for the double-mode cavity with a recombination area at each antinode.

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Improving the viewing angle properties of microcavity OLEDs by using dispersive gratings

Cited by 39 publications

References 21 publications

Indium Tin Oxide Modified by Au and Vanadium Pentoxide as an Efficient Anode for Organic Light-Emitting Devices

Indium Tin Oxide Modified by Au and Vanadium Pentoxide as an Efficient Anode for Organic Light-Emitting Devices

AZO/Ag/AZO anode for resonant cavity red, blue, and yellow organic light emitting diodes

Improvement in viewing angle properties of top-emitting organic light-emitting devices

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