OLED

FTIR spectroscopy and scanning tunneling microscopy (STM) were used to study the molecular organization and morphology of vacuum deposited (VD) thin films of tris (8-hydroxyquinoline) aluminum (Alq3) from metal-organic planar light-emitting nanocomposites consisting of gold island films and VD Alq3 film. It was found that  thermal evaporation in vacuum does not cause dissociation of Alq3, and that the obtained films are essentially amorphous. Reflection-absorption (RA) IR spectra show predominantly perpendicular orientation of quinoline groups of Alq3 molecules in the films towards the substrate. With the STM method, a thickness-dependent structure of the films was found and the first near-surface layers of Alq3 films were characterized. It has been revealed that VD deposited Alq3 films of small thickness (5–15 nm) consist of molecular domains with a particular orientation along the Au[112] direction.

use a low refractive index electron transport layer (ETL). To design a high-efficiency OLED, it is important to have a multilayer structure to control the radiative recombination such that excitons are confined to the emis-sive layer (EML) using high triplet charge blocking layers. In addition to exciton confinement , the electron and hole transport layers should be chosen in such a way to maintain the charge balance to avoid triplet-polaron quenching. In a multilayer OLED, the ETL also plays a key role in determining the light extraction efficiency since it is the intermediate layer between the EML and the metallic cathode, and a large portion of the dipole radiation from the EML is lost to the evanescent region where the in-plane wave-vector is larger than the total wave-vector, resulting in radiation that is coupled to the surface plasmon polariton (SPP) and the " lossy surface waves " on the metallic cathode. [4] The magnitude of the loss to the SPP mode is determined by the dielectric constants of the metallic cathode and the ETL, therefore the refractive index of the ETL can significantly impact the out-coupling efficiency of an OLED. There have been some reports demonstrating the effect of the ETL's refractive index on light extraction efficiency in OLEDs by simulation. [5,6] However, experimental study of the effect of ETL refractive index on device performance is rather limited. [7] In this work, we demonstrate the effect of ETL's refractive index on device efficiency using a solution processed OLED with a copper-based thermally activated delayed fluorescent (TADF) emitter, [(2-(Diphenylphosphino)-4-isobutylpyridine) (PPh3)2Cu2I2] (Cu(I)-iBuPyrPHOS). The emitter has a photolu-minescence quantum yield (PLQY) of 70%. [8] Based on the PLQY and assuming an out-coupling efficiency of 20%, a maximum external quantum efficiency (EQE) of 14% is expected. Using 2,9-di(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (NBPhen) and 2,4,6-tris(biphenyl-3-yl)-1,3,5-triazine (T2T) as ETLs, we showed that an optimized device has a maximum EQE of 12% which is close to the estimate of the maximum EQE of 14%. Surprisingly, using tris-[3-(3-pyridyl)mesityl] borane (3TPYMB) as the ETL we achieved a maximum EQE of 21%, showing nearly a 76% enhancement just by changing the ETL alone. Upon investigation of the origin of the efficiency enhancement, we found that the refractive index of 3TPYMB is 1.65, which is the lowest among all commonly used ETLs, resulting in a significant enhancement in light extraction efficiency. Our device data are also confirmed by the optical simulation results. A low refractive index electron transport layer (ETL) can be very effective in enhancing the out-coupling efficiency of an organic light-emitting diode (OLED). However, most organic films show a refractive index close to 1.8. In this work, it has been discovered that tris-[3-(3-pyridyl)mesityl]borane (3TPYMB) has a low refractive index of 1.65 (at 550 nm), which is the lowest refractive index ETL among the commonly used ETLs up to date. Using 3TPYMB as an ETL, a solution processed OLED is demonstrated with nearly a 76% enhancement in external quantum efficiency (EQE). Optical simulation results of this study show that 59% of the enhancement comes from the low refractive index 3TPYMB, and the remaining 17% from the change in charge balance due to the 3TPYMB ETL in the OLED devices.

In this research the effect of ZnO nanorods is simulated and investigated on the performance of poly (2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylene vinylene (MEH-PPV) based organic light-emitting diode (OLED) located between two electrodes (ITO as an anode and Calcium as a cathode) for emitting in near ultraviolet (UV) region. To study the irradiation in these regions, three structures (ITO/MEH-PPV/Ca, ITO/ZnO/MEH-PPV/Ca and ITO/ZnO/ZnO NR/MEH-PPV/Ca) were considered. Results showed that the OLED simulated with ZnO nanorods had a better performance in comparison with two other structures with higher irradiation intensity at the wave length of 380 nm.

A series of novel highly conjugated Donor-p-Acceptor (D-p-A) chromophores 3(a-g) are designed and synthesized through the Wittig Reaction. These molecules contain an aryl/heteroaryl groups as an electron donor (D) and electron transporting oxadiazole as acceptor (A). The structural integrity of the compounds was characterized by 1 H NMR, 13 C NMR and GC-MS analysis. The photophysical properties have been studied in detail using UV-Vis absorption, fluorescence spectroscopy and time-resolved fluorescence measurements. These synthesized compounds emit intense blue-green-yellow fluorescence with reasonably good quantum yields. In addition, steady-state absorption and fluorescence measurements were carried out in solvents of varying polarities to understand the intramolecular charge-transfer (ICT) characters of these compounds. The solvent dependency of the large Stokes shifts and high dipole moment of excited state also supported the charge-transfer character of the excited state. The combined experimental Cyclic Voltammetry (CV) and theoretical methods (DFT) were performed to investigate structure-property relationship and ICT property of these compounds. The computed values were found to be in good agreement with the experimental results. The results demonstrated that the novel D-p-A chromophores could play important role in organic optoelectronics.

The development of 5G (fifth generation) mobile communication systems was initiated to meet the expected need for higher data rates. In this article, a new 28/38 GHz dual-band “inverted-F” array antenna for 5G applications is proposed. This antenna can be integrated in OLEDs (Organic Light Emitting Diodes) panels which can be used both for lighting or display. This 5G antenna, composed of 32 elements, has the advantage of a dual-band and compact structure. Each element of the array antenna has the shape of an “inverted-F” antenna. This array antenna can cover the 28 GHz band (27.94–28.83 GHz) and the 38 GHz band (37.97–38.96 GHz) with mutual coupling between the elements less than 􀀀35 dB. The characteristics of the end fire radiation beams were obtained by employing an array of 32 “inverted-F” antenna elements on the upper and lower portions of the PCB (Printed Circuit Board). The suggested design has a gain of approximately 16.52 dB at 28.38 GHz and 15.35 dB at 38.49 GHz, which is suitable for 5G mobile communications.