Organic Light Emission Research Articles

5‐4: High Efficiency Top‐Emission Organic Light Emitting Diodes Realized Using Newly Developed Low Absorption Pure Ag cathode Configuration

We report, highly efficient red top emission organic light emitting diodes (TEOLEDs) having thin pristine Ag cathode unit with low absorption, uniform surface morphology and good electron injection property. TEOLEDs with Ag cathode unit exhibit almost 1.4 times improvement in current efficiency as well as low driving voltage compared with widely used Mg:Ag cathode and almost identical lifetime with Mg:Ag cathode.

Tuning the optoelectronic and charge transport properties of 2,5-di(pyrimidin-5-yl)thieno[3,2-b]thiophene by oligocene end cores substitution

Abstract With the focus on tuning the charge transport and optoelectronic properties, various new derivatives were designed by substituting the oligocene moieties at end cores of 2,5-di(pyrimidin-5-yl)thieno[3,2-b]thiophene (Comp.1). The end core substitution effect of benzene, naphthalene, anthracene, tetracene, pentacene and hexacene on Comp.1 was comprehensively studied on the structure-property relationship, electro-optical properties, ionization potential (IP), electron affinity (EA) and hole/electron reorganization energies (λ(h)/λ(e)). The injection barrier was reduced by introducing the oligocene units at end cores. The substitution of anthracene, tetracene, pentacene and hexacene at end cores of Comp.1 significantly minimized the polarization resulting smaller λ(h) (Comp.1c – Comp.1f) than the referenced compound, i.e., pentacene. The smaller λ(h) values are illuminating that newly designed derivatives might be superior/analogous to pentacene, i.e., frequently used hole transport material. The fluorescence spectra, dipole moment, IP, EA and λ(h) values showed that targeted molecules would be not only good for organic light emitters but also efficient for organic semiconductors and photovoltaic devices.

Effects of the Methyl Group on the Emission Efficiency of the Red Phosphorescent Iridium(III) Complexes for OLEDs

Novel red phosphorescent iridium(III) complexes, namely (MN-Q)2Ir(tmd), (MN-MQ)2Ir(tmd), (PT-P)2Ir(tmd) and (PT-MP)2Ir(tmd) were synthesized for the red phosphorescent organic lightemitting diodes (phOLEDs). The ligands have sites of both the electron donor and acceptor in a molecule. The main ligands were synthesized by the Suzuki coupling reaction, and comprised an electron donor and an electron acceptor group. Subsequently, the iridium(III) complexes were synthesized by the Nonoyama reaction and their photochemical luminescence properties were investigated by ultraviolet-visible and photoluminescence spectroscopy. The manufactured devices were characterized by current density-voltage-luminance, power efficiency, external quantum efficiency, as well as their electroluminescence spectra. Finally, the effects of the trifluoromethyl group on the emission efficiency of the organic light-emitting diodes were investigated by comparing the energy levels and luminescence efficiency of the three iridium complexes.

Carbazole and Benzophenone Based Twisted Donor–Acceptor Systems as Solution Processable Green Thermally Activated Delayed Fluorescence Organic Light Emitters

New donor-acceptor (D-A) and donor-acceptor-donor (D-A-D) systems with carbazole and benzophenone moieties as donor and acceptor, respectively, have been synthesized. Photoluminescence quantum yiel...

Dual Emission through Thermally Activated Delayed Fluorescence and Room-Temperature Phosphorescence, and Their Thermal Enhancement via Solid-State Structural Change in a Carbazole-Quinoline Conjugate.

The emergence of single-component organic dual light emitters holds great promise for white light-emitting diodes (WLEDs) and biological detection due to the involvement of broad emission covering visible spectrum. Here we show experimental studies on dual emission of carbazole-quinoline conjugate (CQ) that exhibits both thermally activated delayed fluorescence (TADF) via reverse intersystem crossing (r ISC) from the higher-lying triplet state ( T2) to the singlet state ( S1) and room-temperature phosphorescence (RTP) from the lowest triplet state ( T1) due to low energy gap between T2 and S1, and energetic proximity of T1 with T2. We found in thermal effect that the intensity of the dual features is enhanced with increasing temperatures up to 100 °C, which can be explained by a thermal-induced structural change (TISC) mechanism that compensates the emission losses due to nonradiative transitions at elevated temperatures. This property, in addition to its enhanced TADF and phosphorescence decay rates (∼107 s-1and 101 s-1) at 100 °C, would have great promise for high-efficiency LEDs.

P‐176: Distinquished Poster Paper: The Suppression of Viewing Angle Dependence of Top Emission Organic Light Emitting Diodes Having Strong Microcavity Characteristics by Applying Concave Patterned Anode

In order to obtain the stable viewing angle characteristics of top emission organic light emitting diodes (TEOLEDs) having strong microcavity characteristics, we fabricated nano‐porous film on the glass substrate before depositing highly reflective anode. And then, we could obtain the concave patterned anode by depositing anode on the nano‐porous film and fabricated TEOLED composed of concave patterned layers. From this approach, we could successfully obtain not only the stable color shift and luminance distribution with viewing angle but also high efficiency caused by uneven morphology. In addition, we found that the driving voltage of TEOLED could be reduced due to increased surface area effect of the concave patterned anode, so that the power efficiency was enhanced by about 15% in comparison with reference device.

The suppression of viewing angle dependence of top emission organic light emitting diodes having strong microcavity characteristics by applying concave patterned anode

AbstractIn order to obtain the stable viewing angle characteristics of top emission organic light emitting diodes (TEOLEDs) having strong microcavity characteristics, we fabricated nano‐porous film on the glass substrate before depositing highly reflective anode. And then, we could obtain the concave patterned anode by depositing anode on the nano‐porous film and fabricated TEOLED composed of concave patterned layers. From this approach, we could successfully obtain not only the stable color shift and luminance distribution with viewing angle but also high efficiency caused by uneven morphology. In addition, we found that the driving voltage of TEOLED could be reduced due to increased surface area effect of the concave patterned anode, so that the power efficiency was enhanced by about 15% in comparison with reference device.

Light modulation of top emission organic light emitting diodes showing strong microcavity effect by applying multilayered scattering film.

In order to suppress the viewing angle dependence of top emission organic light emitting diodes (TEOEDs) on a strong microcavity structure, we prepared multi-layered nano scattering film which was consisted with transparent planarizing layer and hazy crosslinked scattering layer. Through such an approach, we could obtain not only a stable color shift and luminance distribution with viewing angle but also a negligible pixel blur level. Meanwhile, we investigated a black tint level of TEOLEDs after attachment of circular polarizer (CP) on various nano scattering films because nano scattering film deteriorates a black level. We found that the black level could be improved from the black tint by reducing the refractive index difference between planarizing layer and scattering layer.

The Improvement of Spectral Stability by Adjusting the Recombination Zone Position in White Phosphorescent Organic Light Emitting

The recombination zone (RZ) position is an important factor for the CIE coordinate and spectral stability. We attempt to fabricate a serials of white phosphorescent organic emitting diode devices with mixed host (mCP:TPBi) multiple EMLs. The RZ position and range can be changed by the concentration ratio of mixed host or guest material, the thickness of the emitting layer (EML) and the structure of EML. Through inserting a mixed host blue emission layer as compensation layer between orange EML and ETL, we obtain a spectral stable device with the maximum luminance, power efficiency and current efficiency of 29790 cd/m2, 23.89 lm/W and 35.94 cd/A, respectively. Then, a more stable device is fabricated by decreasing the thickness of the blue EML, the range of CIE coordinate change is only (0.005, 0.002) when the voltage increases from 4 V to 8 V.

Effect of the distribution of states in amorphous In-Ga-Zn-O layers on the conduction mechanism of thin film transistors on its base

Amorphous In-Ga-Zn-O Thin Film Transistors (a-IGZO TFTs) have proven to be an excellent approach for flat panel display drivers using organic light emitting diodes, due to their high mobility and stability compared to other types of TFTs. These characteristics are related to the specifics of the metal-oxygen-metal bonds, which give raise to spatially distributed s orbitals that can overlap between them. The magnitude of the overlap between s orbitals seems to be little sensitive to the presence of the distorted bonds, allowing high values of mobility, even in devices fabricated at room temperature. In this paper, we show the effect of the distribution of states in the a-IGZO layer on the main conduction mechanism of the a-IGZO TFTs, analyzing the behavior with temperature of the drain current.

Perovskite Quantum Dots with Near Unity Solution and Neat-Film Photoluminescent Quantum Yield by Novel Spray Synthesis.

In this study, a novel perovskite quantum dot (QD) spray-synthesis method is developed by combining traditional perovskite QD synthesis with the technique of spray pyrolysis. By utilizing this new technique, the synthesis of cubic-shaped perovskite QDs with a homogeneous size of 14 nm is demonstrated, which shows an unprecedented stable absolute photoluminescence quantum yield ≈100% in the solution and even in the solid-state neat film. The highly emissive thin films are integrated with light emission devices (LEDs) and organic light emission displays (OLEDs). The color conversion type QD-LED (ccQD-LED) hybrid devices exhibit an extremely saturated green emission, excellent external quantum efficiency of 28.1%, power efficiency of 121 lm W-1 , and extraordinary forward-direction luminescence of 8 500 000 cd m-2 . The conceptual ccQD-OLED hybrid display also successfully demonstrates high-definition still images and moving pictures with a 119% National Television System Committee 1931 color gamut and 123% Digital Cinema Initiatives-P3 color gamut. These very-stable, ultra-bright perovskite QDs have the properties necessary for a variety of useful applications in optoelectronics.

Inkjet printing for electroluminescent devices: emissive materials, film formation, and display prototypes

Inkjet printing (IJP) is a versatile technique for realizing high-accuracy patterns in a cost-effective manner. It is considered to be one of the most promising candidates to replace the expensive thermal evaporation technique, which is hindered by the difficulty of fabricating low-cost, large electroluminescent devices, such as organic lightemitting diodes (OLEDs) and quantum dot light-emitting diodes (QLEDs). In this invited review, we first introduce the recent progress of some printable emissive materials, including polymers, small molecules, and inorganic colloidal quantum dot emitters in OLEDs and QLEDs. Subsequently, we focus on the key factors that influence film formation. By exploring stable ink formulation, selecting print parameters, and implementing droplet deposition control, a uniform film can be obtained, which in turn improves the device performance. Finally, a series of impressive inkjet-printed OLEDs and QLEDs prototype display panels are summarized, suggesting a promising future for IJP in the fabrication of large and high-resolution flat panel displays.

Multiple–color AIE coumarin–based Schiff bases and potential application in yellow OLEDs

Three new coumarin–based derivatives with similar molecular structure were synthesized through a simple Schiff base reaction and their fluorescent properties were investigated in detail. Among of the compounds showed aggregation–induced emission (AIE) characteristics and high quantum efficiency (ΦF), of which compound 1 powder showed the strongest emission peak 570nm (ΦF = 25.3%), compound 2 solid exhibited 610nm fluorescence emission peak (ΦF = 3.3%), while the maximum emission wavelength of compound 3 powder red–shift to 640nm (ΦF = 16.8%). Meanwhile, compounds 1–3 showed long fluorescence lifetimes with respective 8.86μs, 8.97μs and 8.51μs. The appearance of fluorescence properties can be attributed to efficient the excited state intramolecular proton transfer (ESIPT) and the twisted intramolecular charge transfer (TICT). Furthermore, due to the good luminescent properties, high stabilities and the large Stokes–shifts, the three compounds were ideal candidates for promising applications in organic lightemitting diodes (OLEDs).

Lowering the driving voltage and improving the luminance of blue fluorescent organic light-emitting devices by thermal annealing a hole injection layer of pentacene**Project supported by the National Natural Science Foundation of China (Grant No. 60906022), the Natural Science Foundation of Tianjin, China (Grant No. 10JCYBJC01100), the Key Science and Technology Support Program of Tianjin, China (Grant No. 14ZCZDGX00006), and the

We chose pentacene as a hole injection layer (HIL) to fabricate the high performance blue fluorescent organic lightemitting devices (OLEDs). We found that the carrier mobility of the pentacene thin films could be efficiently improved after a critical annealing at temperature 120 °C. Then we performed the tests of scanning electron microscopy, atomic force microscopy, and Kelvin probe to explore the effect of annealing on the pentacene films. The pentacene film exhibited a more crystalline form with better continuities and smoothness after annealing. The optimal device with 120 °C annealed pentacene film and n-doped electron transport layer (ETL) presents a low turn-on voltage of 2.6 V and a highest luminance of 134800 cd/m2 at 12 V, which are reduced by 26% and improved by 50% compared with those of the control device.

P‐169: Solution‐processed Organic Light‐emitting Diodes with a Polymeric Hole Transport Layer Crosslinked by Surface Initiated Oxidative Crosslinking

A surface initiated oxidative coupling method of a carbazole compound was used as a fabrication approach of a crosslinked hole transport layer for solution processed organic light‐emitting diodes. The surface initiated oxidative coupling method was able to avoid damage by the organic solvent in the manufacturing process. Moreover, the hole transport material was able to prevent exciton quenching by the oxidizing agent and solved the problem of luminous efficiency reduction of the organic light emitting device because the oxidant was not in contact with the emitting layer. As a result, the surface initiated oxidative crosslinking method improved the luminous efficiency and lifetime characteristics of the solution processed organic light‐emitting devices.

Suppression of viewing angle dependence of organic light emitting diodes by introduction of circular polarizer with nanoporous polymer film

To improve poor viewing angle characteristics of top emission organic light emitting diodes (TEOLEDs) without any serious pixel blur phenomena, we applied a circular polarizer (CP) film modified by nanoporous polymer film (NPF). From this approach, we could improve the color shift significantly (Δu'v’ in CIE 1976 with viewing angle, from 0.0165 to 0.0114), and expand angular light emission distribution of off-axis by applying CP with NPF. We found that black color shift was little associated with NPF position change although black color was slightly faded tint by applying NPF, as like plasma display panel(PDP)’s off condition. Very interestingly, we found that the reflectance was not changed seriously whether NPF exists between glass encapsulation and CP or not. Besides, we investigated the pixel blur level when we applied different condition in encapsulation thickness and morphology of diffusing films. As a result, we found that the pixel blur phenomena can be significantly suppressed by applying thin encapsulation and NPF type diffuser film.

AC-driven organic light emission devices with carbon nanotubes

We have investigated alternating current (AC)-driven organic light-emitting devices (OLEDs), with carbon nanotubes (CNTs) incorporated within the emission layer. With CNT incorporation, the brightness of the OLEDs was substantially improved, and the turn-on voltage was reduced by at least a factor of five. Furthermore, the current levels of the CNT-incorporated OLEDs were lower than that of the reference device. A roughly 70% decrease in the current level was obtained for a CNT concentration of 0.03 wt%. This was accomplished by keeping the concentration of CNTs low and the length of CNTs short, which helped to suppress the percolation networking of CNTs within the emitting layer. Strong local electric fields near the end-tips of CNTs and micro-capacitors formed by dispersed CNTs might have caused this high brightness and these low currents. CNT incorporation in the emitting layer can improve the characteristics of AC-driven OLEDs, which are considered to be one of the candidates for flat panel displays and lightning devices.

Conductive polymer nanocomposites: a critical review of modern advanced devices

Conductive polymer nanocomposites have found applications in advanced devices: organic light emission diodes, organic photovoltaics, electrochromic devices, and others.

Development of plasma assisted thermal vapor deposition technique for high-quality thin film.

The novel technique of Plasma-Assisted Vapor Deposition (PAVD) is developed as a new deposition method for thin metal films. The PAVD technique yields a high-quality thin film without any heating of the substrate because evaporated particles acquire energy from plasma that is confined to the inside of the evaporation source. Experiments of silver thin film deposition have been carried out in conditions of pressure lower than 10-3 Pa. Pure silver plasma generation is verified by the measurement of the Ag-I peak using optical emission spectroscopy. A four point probe and a UV-VIS spectrophotometer are used to measure the electrical and optical properties of the silver film that is deposited by PAVD. For an ultra-thin silver film with a thickness of 6.5 nm, we obtain the result of high-performance silver film properties, including a sheet resistance <20 Ω sq-1 and a visible-range transmittance >75%. The PAVD-film properties show a low sheet resistance of 30% and the same transmittance with conventional thermal evaporation film. In the PAVD source, highly energetic particles and UV from plasma do not reach the substrate because the plasma is completely shielded by the optimized nozzle of the crucible. This new PAVD technique could be a realistic solution to improve the qualities of transparent electrodes for organic light emission device fabrication without causing damage to the organic layers.

On-Display Transparent Half-Diamond Pattern Capacitive Fingerprint Sensor Compatible With AMOLED Display

The need for personal security in portable devices has increased. Among several biometric sensing technologies, fingerprint sensing is the most highlighted method. However, a fingerprint sensor in electronics is stifling the demands for a larger interactive display. In this paper, the bottlenecks of placing the sensor on display is discussed, and an on-display mutual capacitive high-resolution transparent fingerprint sensor with a half-diamond pattern is proposed for adapting to the needs of personal security on a larger screen. To overcome various performance limitations on the on-display fingerprint sensor, a metal mesh is used as an electrode material, and the half-diamond pattern is applied. The proposed pattern is compatible with the diamond-patterned active matrix organic light emitter diode display. The proposed sensor has $72\times72$ channels in a 6 mm $\times6$ mm area. The sensor satisfies the criteria set by the Federal Bureau of Investigation for fingerprint sensing with 322 capacitors per inch, and the measured transmittance in the visible light region is 79.7%. The proposed sensor achieved a capacitance variation 2.3 times larger than that achieved by the conventional sensor. The five-channel fingerprint sensing circuit to examine the feasibility of fingerprint detection is fabricated with the TSMC 0.18- $\mu \text{m}$ process.