Performance Of Organic Electroluminescent Devices Research Articles

A Study on Effects of Hole Blocking and Luminescence Characteristics of Blue-Light Material DPVBi on Performance of Organic Electroluminescent Devices

A Study on Effects of Hole Blocking and Luminescence Characteristics of Blue-Light Material DPVBi on Performance of Organic Electroluminescent Devices

Study on Work Function of Modified Indium Tin Oxide and Performance of Organic Electroluminescent Devices.

ABSTRACTThe work function of the indium tin oxide electrode (ITO) modified by a self-assembled monolayer (SAM), which is used as an electrode in organic electroluminescent (EL) devices, was investigated in this study. It is revealed that chemical modification of ITO with p-substituted with different terminal groups (NH2−, Cl−, and CF3−) benzoic acids as a SAMs material with carboxyl binding group is caused to increase the work function of the ITO electrode. Through a self-assembly process, the transmittance of the ITO with a SAM was not changed. The work function change of ITO with various SAM was measured by using cyclic voltammetry. Characteristics of EL devices were increased because the energy barrier was decreased in an interface between the ITO and an organic layer in the EL devices. The correlation of the work function change and the performance of the chemically modified EL devices was estimated.

Nanovoid nature and compression effects in organic light emitting diode

Compressing the organic layers in organic light emitting diode (OLED) is introduced as an effective process for improving the performance of organic electroluminescent devices. This process involves applying physical pressure to the organic layers of the device. The OLED fabricated by this method shows a notable increase in luminance intensity and current efficiency when compared with compression-free device, the current efficiency almost doubling. The organic layers have nanovoids and the compression results in a denser packing of organic molecules, leading to a better charge transport.

Effect of LiF buffer layer on the performance of organic electroluminescent devices

Inserting LiF buffer layer between NPB and Alq 3 can also enhance the efficiency of the device. A 0.3 nm LiF layer shows the optimal effects in this work, explained based on tunneling theory. The device with two LiF buffer layers both at the organic–organic interface and at the cathode–organic interface respectively showed the highest luminance of 23000 cd/m 2 at a fixed bias of 20 V.

A Study on Highly Efficient Organic Electroluminescent Devices

In order to improve the device performances of organic electroluminescent devices (OELDs), the efficiency of carrier injections into the organic layers from electrodes and the balance of injected carrier densities in the emission region are critical factors. Especially, energy barriers, which exist at the interfaces between electrodes and organic layers, interrupt carrier injections, which lead to unbalanced carrier densities. In this study α-septithiophene (α-7T), as a buffer layer, and composite cathode composed of Al and CsF were formed to improve hole and electron injections, respectively. The orientations of α-7T molecules were adjusted using the simple rubbing method and the mass ratio of CsF was varied from 1 to 10 wt%. Upon investigation of we believe that the 3 wt% mass ratio of CsF and the horizontal orientation of α-7T molecules are the optimized conditions for achieving better the performance of OELDs. Device with the horizontally oriented 20 nm thick α-7T layer and composite cathode shows a turn-on voltage of 7V and luminance of 172 cd/m² at 4 mA/cm².

Effect of LiF buffer layer on the performance of organic electroluminescent devices

A novel device using a LiF layer both at the anode–organic interface and at the cathode–organic interface was fabricated, combining a weakened hole injection with enhanced electron injection. The device showed the highest luminance of 21 000 cd/m 2 at a fixed bias of 12 V. The device exhibits a steeper I– V characteristic and a higher brightness than that of the devices of other structures. The steeper I– V characteristic of the device may be useful to an organic electrically pumped laser.

Effects of the morphologies and structures of light-emitting layers on the performance of organic electroluminescent devices

Organic electroluminescent devices with a structure of ITO/ploy (9-vinylcarbazole)/tris (8-hydroxyquinoline) aluminum (Alq3)/Mg:Ag are fabricated at different substrate temperatures (77, 298, and 438 K) during Alq3 deposition. It is found that the surface morphologies of Alq3 thin films greatly affect the I–V characteristics of the devices by the contact area between metal cathode and light-emitting layer. There is an increase in the luminous efficiency of the devices in the order 77 K<298 K<438 K. We attribute this trend to different structures of Alq3 thin films.

Short-term degradation behaviors of light emitting diodes made of polyurethane derivative with large permanent dipoles on the side chain

The effect of permanent dipole on the performance of organic electroluminescent devices (OELDs) was investigated by using a model polyurethane derivative (PU) with large dipoles on its side chain. The used OLEDs emits green color with an emission maximum at 540 nm. Decreases in luminance and current density during a constant voltage driving were observed. Evident spontaneous recovery and reverse bias assisted recovery of the degradation were confirmed. The observed degradation and recovery phenomena were discussed in terms of internal electronic field formation due to the re-orientation of dipole in organic layer.

The Internal Field Distribution in Light Emitting Electrochemical Cells and Light Emitting Diodes: A Comparative Study

ABSTRACTWe determined the internal electric field distribution in light emitting electro-chemical cells (LECs) and light emitting diodes (LEDs) based on methyl substituted poly(paraphenylen) (mLPPP) by performing electroabsorption measurements as a function of an external bias voltage. Based on these results we outline the working principle of both types of devices. In the case of the LEC we observed an abrupt increase in the EA signal above a threshold voltage of about 2V which we attributed to junction formation due to in-situ electrochemical doping. For single layer LEDs we found the behavior expected for metal/insulator/metal/structures, i.e. the electric field drops linearly over the bulk polymer and no space-charge regions were observed.These findings are important for improving the performance of organic electroluminescent devices.

Effect of a plasma treatment of ITO on the performance of organic electroluminescent devices

We investigated the effect of plasma treatments of indium-tin oxide (ITO) surface on the performance of electroluminescent (EL) devices using different gases. In the case of air or argon, an intense EL emission was observed at low applied voltages. On the other hand, when hydrogen was used, very high voltages were needed to obtain the EL emission. The change in voltage was attributed to the removal of contaminants and to the change in work function of ITO. For the devices with the ITO treated with hydrogen plasma, the EL efficiency was very low. This result suggested that electrons accumulated at the organic/organic interface exert a harmful effect on the light emission.