Ultra-high resolution organic light emitting diodes with color

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Ultra-high resolution organic light emitting diodes with color conversion electrode Jun Hee Han, Dohong Kim, Tae-Woo Lee, Eun Gyo Jeong, Hoseung Lee, and Kyung Cheol Choi ACS Photonics, Just Accepted Manuscript • DOI: 10.1021/acsphotonics.8b00230 • Publication Date (Web): 28 Mar 2018 Downloaded from http://pubs.acs.org on March 28, 2018

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ACS Photonics

Ultra-high resolution organic light emitting diodes with color conversion electrode Jun Hee Han†, Dohong Kim†, Tae-Woo Lee†, Eun Gyo Jeong†, Ho Seung Lee† and Kyung Cheol Choi†,*

†

School of Electrical Engineering, the Korea Advanced Institute of Science and Technology,

Yuseong-gu, Daejeon 34141, Republic of Korea

KEYWORDS. high resolution, subwavelength optics, color conversion, light resonance, optical film, organic light emitting diodes

ACS Paragon Plus Environment

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ABSTRACT.

The implementation of ultra-high resolution displays is one of the important technologies for advanced displays. In this paper, an ultra-high resolution organic light emitting diode display is implemented without fine metal mask method, but via a color conversion electrode. A red and green color ultra-high resolution organic light emitting diode display with a pixel size of 5 μm was experimentally realized without changing any aspects of the structure of the OLEDs display except for the precisely fine patterned color conversion electrode. Furthermore, nm scale pixel size can be expected through this method. The color conversion electrode is a multilayer structured nm thick conductive optical film, and its applicability was confirmed based on a theoretical analysis and optical simulation. The ultra-high resolution display with color conversion electrode could be a basis technology for the development of advanced high resolution displays.


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Main Manuscript. One of the main streams of display development is ultra-high resolution displays. However, the development of such an ultra-high resolution technology has not progressed, especially for the organic light emitting diode (OLED) display. There are several problems that should be overcome for implementation of ultra-high resolution OLED displays including the realization of a highly integrated driving circuit and enhancing the mobility of thin film transistors. Among the various problems, however, the most urgent issue to be solved is reducing the pixel size of the display.

1,2

Especially for the virtual reality display in which the feeling of immersion is

important, display resolution of at least 8K is required to reduce the screen door effect reflecting a problem of pixel identification due to large pixel size, and it means that the pixel size should be reduced to sub-micrometer units. In the case of OLEDs, a fine metal mask is used for pixel discrimination. However, when this mask is used, there is a limitation to reduce the pixel size, which remains an obstacle to realizing ultra-high resolution displays. In order to solve the high resolution problem, structure consisting of white emission and a color filter has been suggested. Therefore, various studies have been conducted to implement a color filter in a narrow region, because an important factor determining the pixel size is the color filter. 3–5 However, the works in previous studies were difficult to commercialize due to technical reasons or a complicated fabrication process. The studies using an inkjet have been carried out to realize the fine pixel size, but the materials that can be used for the inkjet method have to be further developed and the process steps have to be simplified. 6,7 In this study, an ultra-high resolution OLED display was implemented by introducing a color conversion electrode (CCE). The principle of changing the color using CCE is cavity effect. Unlike typical cavity effect, however, the CCE can change the emissive color of the device while


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maintaining the thickness and type of the organic materials, and electrical properties of the devices. Therefore, a red and green colored ultra-high resolution OLEDs display with a pixel size of 5 µm was experimentally realized based on yellow emission layer without changing any aspects of the structure of the display except the fine patterned CCE. The principle of color tuning by the CCE was theoretically analyzed and optimized conditions of the CCE were designed using an optical simulation. The CCE is advantageous in terms of efficiency and this was confirmed by theoretical and experimental analyses. The experimental and simulation results demonstrate remarkable potential to realize various shaped nm scale pixels and utilization in the full colored ultra-high resolution OLED display composed of red, green, and blue subpixels.


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Figure 1. Design overview of suggested color conversion electrode. (a) Schematic device structure of organic light emitting diodes with color conversion electrode. (b) Graphical representation of the light interference within an organic light emitting diode. (c) Graphical representation of the electric and magnetic field inside the multilayer structure.


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Figure 1(a) shows the structure of the OLED with a CCE for an ultra-high resolution display. As shown in the structure, the device is a bottom emission display, in which a CCE, a hole transport layer (HTL), an emission layer (EML), and a cathode are stacked on a substrate. The CCE consists of a structure wherein silver (Ag) thin films and tungsten trioxide (WO3) thin films are alternately stacked. In this study, the key technology to realize the ultra-high resolution OLED display is the CCE. Gcav (λ ) = f FP (λ ) ⋅ fTI (λ ; d1 )

(eq. 1)

f T I ( λ ; d 1 ) = 1 + ( r1 ⋅ e − κ k 0 2 d1 ) 2 + 2 ⋅ r1 ⋅ e − κ k 0 2 d1 ⋅ cos ∆ φ TI

(eq. 2)

f FP (λ ) =

t2

2

∆φ (1 − R ) + 4 R (sin FP ) 2 2

(eq. 3)

2

In the OLED device, which has a stacked thin film structure with a sub-wavelength scale thickness, the light interference in the device affects the emitting color of the device. Light interference in the device can be expressed as cavity gain ( GCAV ), a product of the Fabry-Perot factor ( f FP ) and the two-beam interference factor ( f TI ). (Eq. 1, Eq. 2, Eq. 3)

8,9

Figure 1(b)

schematically shows two-beam interference and Fabry-Perot within the device. In Eq. 1, λ is wavelength and d1 is the distance between the dipole and reflector 1. A detailed formula for the cavity gain is summarized in the supplementary information. Generally, in order to tune the emitting light color, a method of changing the distance between reflector 1 and reflector 2 ( d 2 ) is used. 10–12 When using this method, the thickness of the organic layer such as HTL and EML must be changed for a specific color, and those change affects the electrical properties of the device such as charge balance. However, by using the CCE proposed in this study, it is possible to tune the emitted light color by changing the reflection coefficient


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and transmission coefficient of the CCE without changing the thickness of the organic layers. In other words, it is possible to control the electrical and optical properties of the device individually with the CCE. This is confirmed from the formula delineating that the Fabry-Perot factor can be changed by only changing the reflection coefficient and transmission coefficient of the CCE. (Eq. 3)

i sin ∆φ1    E1   cos ∆φ1  cos ∆φ2 Y = 1      H1   iY sin ∆φ cos ∆φ  iY sin ∆φ 1 1  2 2  1

i sin ∆φ2    cos ∆φ(n−1) Y2 K  cos ∆φ2   iY( n−1) sin ∆φ( n−1)

i sin ∆φ(n−1)   E  Y(n−1)   n   Hn  cos ∆φ(n−1) 

% d ) ( where , ∆ φ n = nk 0 n

(eq. 4.)

1 B E1 H ,C ≡ 1 )   = [ M ]  Y  ( where, B ≡ En En C   n

(eq. 5.)

Y B −C R= r = 0 Y0 B + C

2

2

2Y0 T=t = Y0 B + C

(eq. 6.)

2

2

(eq. 7.)

The principle of changing the reflection coefficient of the CCE is also light interference. As shown in Figure 1(a), the CCE consists of a multi stack of thin films. When light is incident on the multi-layered film, transmitted light and reflected light are generated in each layer. Finally, reflection and transmission of the entire film are determined through interference of these lights. A graphical representation of this phenomenon is shown in Figure 1(c). The reflection and


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transmission of the CCE can be calculated using a characteristic matrix, such as Eq. 4. The general form of Eq. 4 can be represented as Eq. 5, and reflectance and transmittance can be simply calculated using the variable of Eq. 5. (Eq. 6, Eq. 7) 8,9,13 In Eq. 4 and Eq. 5, En and Hn are electric field and magnetic field at boundary n (interface between material n-1 and material n), respectively, and Yn is optical admittance of material n. In order to change the reflection coefficient and transmission coefficient of the CCE, it is necessary to change the refractive index of each layer or to change the thickness of each layer. In this study, optimized thicknesses of each layer were used to control the reflection coefficient and transmission coefficient of the CCE, while fixing the material as Ag and WO3. A detailed solution of the characteristic matrix, the reflection coefficient and the transmission coefficient are summarized in the supplementary information. Previous works experimentally demonstrated that the multilayer structure of Ag and WO3 is a highly conductive optical film and that this film can be sufficiently applied as an electrode in OLED devices.

5,13,14

Based on these results, a CCE consisting of Ag and WO3 was

simultaneously used as an electrode and an optical film in the display device for this study.


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Figure 2. Simulation results of the optimization of color conversion electrode. (a), (b) Calculation results to obtain the optimized conditions of the color conversion electrode for green and red by a MATLAB simulation, respectively. (c), (d) Calculated simulation data of FabryPerot factor and emission spectrum with green and red color conversion electrode, respectively. The solid lines indicate the Fabry-Perot factor. The colored area shows the emission spectrum. The yellow dashed line is the emission spectrum of the reference device.

The optimized conditions of the CCE for green and red were obtained by calculating the optical functions with MATLAB. The CCE is defined as the optimized CCE when the color


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coordination of the emission light from the OLED with CCE is located close to the green and red coordination of sRGB. Figures 2(a) and 2(b) show simulation results according to thicknesses of the WO3 layers within the CCE. As the emission color coordination of the OLED device is closer to the color coordination of green and red of sRGB in the optimization process, the simulation results have a larger value because the reciprocal of the distance between the emission color coordination and sRGB coordination is set as the simulation results. A wider range of the simulation results of Figures 2(a) and 2(b) can be seen in Figure S1. Table 1 summarizes the optimized layer thickness of the CCE to obtain the green and red light from the simulation results.

Table 1. Optimized layer thicknesses of color conversion electrode

Material Ag

2nd WO3 (y nm)

Ag

1st WO3 (x nm)

Green

10 nm

76 nm

20 nm

109 nm

Red

10 nm

137 nm

20 nm

101 nm

Color

Figures 2(c) and 2(d) show the simulation results of the emission spectrum of the OLED device with the optimized CCE for green and red color, respectively. The OLED structure used in the simulation is the same structure as in Figure 1(a). The reference OLED device uses a transparent electrode of a thin Ag film with a capping layer instead of the CCE to observe the optical properties while the electrical characteristics are the same as those of the CCE (Figure S2) because electrical properties can affect the performance and hinder accurate analysis of the device. The refractive index for each material used in the simulation was obtained by


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measurement except for aluminum (Figure S3). Furthermore, measured data of the photoluminescence (PL) spectrum of the emission layer was used to calculate the emission spectrum (Figure S4). The colored region in each graph is the simulated OLED emission spectrum with green and red CCE, respectively. The emission spectrum of a reference transparent electrode is shown as a yellow dashed line. The cavity gain value according to the CCE is also shown in the graph as a solid line. In the graph, it can be seen that the Fabry-Perot factors of green and red have maximum values in the region of green and red wavelength, respectively. The emission spectrums calculated by the product of the cavity gain and the PL intensity of the emission layer also have the shape of green and red. Simulation results show that the reflection phase of each CCE and the transparent electrode is changed (Figure S5), and this confirms that the basic principle of color tuning through the CCE is to change the reflection coefficient and the transmission coefficient of the CCE while keeping the thickness of the organic layer constant (Eq. 3). The green and red emission spectrums obtained from the OLED with the CCE show higher peak values than the reference device in the simulation. These results suggest that the CCE can achieve improved efficiency relative to the case using a color filter made with dye or pigment. Because the principle of dye and pigment color filter is light absorption, the emission spectrum of the device with the color filter will always have a lower value than the reference device. The principle of efficiency improvement is based on the cavity effect using constructive light interference. In order to confirm the advantage of the CCE in terms of optical properties, an OLEDs with a thick metal electrode that makes efficient use of the cavity effect was compared with the OLED


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with the CCE. An Ag film of 30 nm thickness was used as the thick metal electrode, considering the color purity and efficiency (Figure S6). The thickness of 30 nm is also a value that agrees with the sum of the Ag thickness of the CCE. In the simulation, it is confirmed that there is almost no difference in the optical aspect of the CCE compared with the case of using the thick metal electrode (Figure S7). The simulation was also conducted to determine if the color can be changed in the device consisting of the thick metal electrode by varying the thickness of the capping layer while maintaining the distance between the cathode and the anode. However, the peak wavelength of the emission spectrum was barely changed (Figure S8). These results show that the use of the CCE can take advantage of not only the optical aspect of the thick metal electrode but also the same organic thickness and the same electrical property regardless of emission color. Tuning the color without changing the organic thickness is also an advantage in implementing an ultra-high resolution display. Because high resolution display made by adjusting the thickness of the organic materials cannot be realized with existing fabrication method such as fine patterned thin metal mask technique. Since the yellow color emitting material was used as the emission layer, the colors of the OLEDs were experimentally tuned to green and red. If the emission layer can emit white light, it can be confirmed that the basic three primary colors of blue, green, and red can be implemented with the CCE by the simulation results (Figure S9).


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Figure 3. Performance of organic light emitting diodes with the color conversion electrode (a) Simulated and measured emission spectrum of OLEDs with CCE. Green open and solid rectangular are simulated and measured data for the green emission device, respectively. Yellow open and solid triangles are simulated and measured data for reference device, respectively. Red open and solid circles are simulated and measured data for red emission device, respectively. (b) CIE 1931 diagram of green, red, and reference devices. Circles are experimental data and stars are simulated data. Inset images are the pixel images of the green, red, and reference devices. (c) Current density versus voltage characteristics. (d) Luminance versus current density


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characteristics. (e) Current efficiency versus luminance characteristics. For (c), (d), and (e), green solid rectangular, yellow solid triangles, and red solid circles are green emission device, reference device, and red emission device, respectively. (f), (g), (h) Scanning electron microscope images of reference device, green emission device, and red emission device, respectively. The scale bars are 100 nm.

Figure 3(a) shows the emissive spectrums of the fabricated devices and of the simulation. The solid mark is the measured data by the actual experiment and the left y-axis corresponds to the data. Data obtained through simulation are open marks, and the right y-axis corresponds to the data. Figure 3(b) shows the measured color coordination from the fabricated device and the color coordination obtained from simulation results on CIE 1931. The color coordination marked on CIE 1931 show that it shifts to green and red from the yellow when the CCE is applied to the OLED device, and the actual pixel image also shows that the color changed significantly. The color coordination values of green and red of the fabricated devices are (0.367, 0.618) and (0.615, 0.383), respectively. The expected color coordination from the simulation is (0.379, 0.607), (0.626, 0.372), respectively. The experimental and simulation values almost coincide. Figure 3(c) shows the current density (J) versus voltage (V) graph of the fabricated device. When fabricating the OLEDs with the CCE, there was no modification in the thickness of the organic layer, and hence the JV characteristics were the same irrespective of the emissive color. Even the charge balance was also the same, because the thicknesses of HTL and EML were equal. These results suggest that the optical and electrical properties can be controlled individually with the CCE. Previous reports and our experimental results confirmed that the thickness of the HTL affects the electrical properties and the performance of the device (Figure S10). 10,15,16 Figure 3(d) shows the


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luminance versus current density results, and Figure 3(e) shows the current efficiency versus luminance results, averaged over five devices. In the simulation, the calculation is performed considering only the optical properties of the device, assuming that the electrical properties are the same. As Figure 3(a) shows, the simulation and measured data have a similar spectrum shape because the assumption that the devices have the same electrical properties including charge balance regardless of color was satisfied in the experiment. Another reason is that when the CCE is applied to an actual device, the light interference works as designed by theory and simulation. All devices were measured with the same current density of 1 mA/cm2. In Figure 3(a), the peak value of red is much higher than the peak value of green, but the efficiency of green is higher than that of red, as shown in Figure 3(e). This is because the current efficiency is measured considering the luminosity function and the luminosity function has a higher value on the green region than on the red region. Figure 3(a) shows that the spectrum peak value of the device with the CCE is higher than that of the reference device, not only in the simulation but also in the experimental data. As described above, the results verify that higher device efficiency can be expected when fabricating OLEDs using the CCE rather than OLEDs using a color filter of dye and pigment. In Figures 3(f), 3(g), and 3(h), the cross sections of the reference device and that of green and red devices with the CCE were observed by a scanning electron microscope (SEM). The images confirm that the thicknesses are nearly equal to the optimized values by the simulation. Furthermore, it is shown that all devices have the same thickness of HTL, EML, and cathode


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regardless of the color. In the case of the reference, the thin Ag film is more clearly seen by the back scattered electrons (Figure S11). In addition, the angular characteristics of the emission spectrum were also analyzed. The spectrum tended to blue shift according to the angle in both the green and red devices. When the angle was changed to 60 degrees, the peak wavelengths were shifted by about 15 nm and 55 nm for the green and red spectrum, respectively. (Figure S12) This angular dependency is due to the fact that the basic principle of controlling the color is based on the cavity resonance. The proposed method in this study would not be a problem when the viewer faces the screen in the normal direction, but further study on the robust angular property is needed to increase the field of view of the display. In this regard, various studies have been conducted. For instance, researchers have shown that the angular dependency can be reduced when polarized transverse magnetic wave is induced into multilayer structured film like CCE because optical admittance of film is negligibly changed when the angle of incidence of the transverse magnetic wave is different. 17–19 (Figure S13)


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Figure 4. Ultra-high resolution display. (a) Schematic of fabrication process of ultra-high resolution display. (b) Atomic force microscope images of the patterned CCE (c) Cross section profile of patterned CCE obtained by atomic force microscope. (d), (e) Optical microscope images of ultra-high resolution green and red display, respectively. The scale bars are 50 μm.

Our previous reports have already confirmed that a conductive optical film consisting of WO3 and Ag can be fine patterned by photolithography.

5,13

Since the CCE is also composed of WO3

and Ag, fine patterning is possible with photolithography. The use of a fine patterned CCE


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enables easy implementation of ultra-high resolution displays. Figure 4(a) shows a schematic illustration of the fabrication process of the ultra-high resolution display with the CCE. First, the red or green CCE is formed on the patterned negative photo resist (PR) by thermal evaporation. The PR is then stripped, producing a fine patterned CCE. An ultra-high resolution display can be achieved simply by depositing an EML layer and a cathode on the fine patterned CCE. As in the previous experimental confirmation, the thickness and material of all layers between the two electrodes are same, and thus all fabrication processes are exactly the same regardless of color except for the use of the CCE. Furthermore, the OLED device in which red and green color pixels are alternately emitted can be easily implemented by repeating the patterning steps. (Figure S14) This shows that the CCE is advantageous in terms of the fabrication process even for ultra-high resolution displays. Figures 4(b) and 4(c) are atomic force microscope (AFM) data. This shows that the CCE is patterned and strictly divided into about 5 µm width. When the AFM data was analyzed, the root mean square surface roughness value of the patterned CCE was about 3nm. Flattening the electrode surface is an essential condition for stable OLED operation, and the fine patterned CCE satisfied this. Figures 4(d) and 4(e) show ultra-high resolution green and red OLED pixel images fabricated through the process shown in Figure 4(a). Even with µm scale pixel size, the colors can be represented through the CCE. The experimental data confirmed that the proposed CCE can realize a pixel size of μm scale without any problems. This pixel size is smaller than the pixel size of tens of µm used in conventional displays. 20,21 The pixel was line shaped in a size of µm scale, because the PR was patterned in the laboratory unit. However, the implementation of various shaped nm scale pixels can be expected because nm scale patterning of PR is possible in the industry. 22 Although a single color ultra-high resolution display was fabricated in this study,


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it would be easy to produce an ultra-high resolution display composed of basic colors such as blue, green, and red at an industrial level where the patterning process is well established. In summary, we demonstrated an ultra-high resolution OLED display with a CCE. It was theoretically and experimentally confirmed that an ultra-high resolution green and red display with a pixel size of a few µm scale can be successfully implemented with a fine patterned CCE without changing the thickness and type of the organic materials, and electrical properties of the devices. The results of this study demonstrate remarkable potential to realize various shaped nm scale pixels and also show the possibility of high utilization in the display industry. It is expected that this CCE based technology can provide a foundation for development of advanced displays requiring ultra-high resolution such as virtual reality displays, micro displays, etc.

Method. The suggested ultra-high resolution display was manufactured on a cleaned glass substrate. Negative photoresist (NR9-3000PY, FUTURREX INC.) was spin-coated on the cleaned substrate. Then the photoresist was soft-baked at 150 °C for 3 minutes inside an oven. The photoresist coated substrate was exposed to ultraviolet light (UV) with a 360 mJ/cm2 exposure dose with a patterned chrome mask. The photoresist coated substrate was baked again at 110 °C inside the oven for 2 minutes. After the baking process, the photoresist was developed for 17 seconds in an AZ300MIF developer. After the photoresist was patterned, color conversion electrodes and a hole transport layer were deposited on the patterned photoresist substrate by thermal evaporation with a vacuum pressure of less than 6×10-6 Torr: WO3 (x nm) / Ag (20 nm) / WO3 (y nm) / Ag (10 nm) / WO3 (70 nm). WO3 (1-4 mm pcs 4N, TASCO) and Ag (3-5 mm


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granule 4N, TASCO) were used for the fabrication of the color conversion electrode. After the color conversion electrode was deposited on the patterned photoresist, the photoresist was stripped by acetone sonication cleaning for 10 minutes. Super yellow (PDY-132) of 65 nm thickness was spin-coated on the patterned color conversion electrode in a nitrogen atmosphere. The substrates were then loaded into a thermal evaporation chamber, where the cathode was deposited in a vacuum pressure of less than 6 × 10-6 Torr: lithium quinolate (Liq) (1 nm) / aluminum (Al) (100 nm). In the case of the reference device, the transparent electrode and the hole transport layer were deposited on the cleaned substrate by thermal evaporation with a vacuum pressure of less than 6×10-6 Torr: WO3 (41 nm) / Ag (12 nm) / WO3 (70 nm). Super yellow (PDY-132) of 65 nm thickness was then spin-coated on the patterned color conversion electrode in a nitrogen atmosphere. The substrates were loaded into a thermal evaporation chamber, where the cathode was deposited in a vacuum pressure of less than 6×10-6 Torr: lithium quinolate (Liq) (1 nm) / aluminum (Al) (100 nm). A sourcemeter (2400, Keithley) and a spectroradiameter (CS-2000, Konica Minolta) were used to measure the electrical and optical characteristics of the OLED. The refractive indices of Ag, WO3, Al, and PDY-132 were measured experimentally by a spectroscopic ellipsometer (M2000D). Calculations of the optical functions were performed using MATLAB (MathWorks).


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ASSOCIATED CONTENT A detailed formula for the avity gain and characteristic matrix. The optimization of reference device and the results of optical and electrical phenomenon of the OLED devices with and without CCE. The angular characteristis of the emission spectrum. The fabrication process for the ultra-high resolution display (alternately emitted version).

AUTHOR INFORMATION

Corresponding Author K.C. Choi.* Author is with the School of Electrical Engineering, the Korea Advanced Institute of Science and Technology, Yuseong-gu, Daejeon 34141, Republic of Korea (corresponding author phone: +82-42-350-3482; fax: +82-42-350-8082; e-mail: kyungcc@ kaist.ac.kr).

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.


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ACKNOWLEDGMENT This work was supported by the Engineering Research Center of Excellence (ERC) Program supported by National Research Foundation (NRF), Korean Ministry of Science & ICT (MSIT) (Grant No. NRF-2017R1A5A1014708). This research was supported by Nano·Material Technology Development Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Science, ICT and Future Planning(NRF-2016M3A7B4910635). This work was also supported and funded by LG Display Co., LTD.

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For Table of Contents Use Only

Manuscript ID: ph-2018-00230m Manuscript Title: Ultra-high resolution organic light emitting diodes with color conversion electrode

Manuscript Authors: Jun Hee Han, Dohong Kim, Tae-Woo Lee, Eun Gyo Jeong, Ho Seung Lee and Kyung Cheol Choi*

Brief synopsis: An ultra-high resolution OLED display was demonstrated with a color conversing electrode. The results of this study demonstrate remarkable potential to realize various shaped nm scale pixels and also show the possibility of high utilization in the display industry.

Describing the graphics: Graph shows the optical microscope images of ultra-high resolution green and red display. The line width is 5 um.


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Figure 1. Design overview of suggested color conversion electrode. (a) Schematic device structure of organic light emitting diodes with color conversion electrode. (b) Graphical representation of the light interference within an organic light emitting diode. (c) Graphical representation of the electric and magnetic field inside the multilayer structure. 221x380mm (300 x 300 DPI)


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Figure 2. Simulation results of the optimization of color conversion electrode. (a), (b) Calculation results to obtain the optimized conditions of the color conversion electrode for green and red by a MATLAB simulation, respectively. (c), (d) Calculated simulation data of Fabry-Perot factor and emission spectrum with green and red color conversion electrode, respectively. The solid lines indicate the Fabry-Perot factor. The colored area shows the emission spectrum. The yellow dashed line is the emission spectrum of the reference device. 140x108mm (300 x 300 DPI)


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Figure 3. Performance of organic light emitting diodes with the color conversion electrode (a) Simulated and measured emission spectrum of OLEDs with CCE. Green open and solid rectangular are simulated and measured data for the green emission device, respectively. Yellow open and solid triangles are simulated and measured data for reference device, respectively. Red open and solid circles are simulated and measured data for red emission device, respectively. (b) CIE 1931 diagram of green, red, and reference devices. Circles are experimental data and stars are simulated data. Inset images are the pixel images of the green, red, and reference devices. (c) Current density versus voltage characteristics. (d) Luminance versus current density characteristics. (e) Current efficiency versus luminance characteristics. For (c), (d), and (e), green solid rectangular, yellow solid triangles, and red solid circles are green emission device, reference device, and red emission device, respectively. (f), (g), (h) Scanning electron microscope images of reference device, green emission device, and red emission device, respectively. The scale bars are 100 nm. 192x165mm (300 x 300 DPI)


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Figure 4. Ultra-high resolution display. (a) Schematic of fabrication process of ultra-high resolution display. (b) Atomic force microscope images of the patterned CCE (c) Cross section profile of patterned CCE obtained by atomic force microscope. (d), (e) Optical microscope images of ultra-high resolution green and red display, respectively. The scale bars are 50 µm. 158x138mm (300 x 300 DPI)


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Ultra-high resolution organic light emitting diodes with color

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