Layer In Organic Light-emitting Devices Research Articles

Interface formation between NPB and processed indium tin oxide

We have investigated the interface formation between ITO and N, N′-bis-(1-naphthyl)- N, N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB), an organic materials often used as hole transport layer in organic light-emitting devices (OLED), by using X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) and atomic force microscopy (AFM). Acid or base treatment of indium tin oxide (ITO) surfaces can significantly alter the surface work function which, in the case of acid treatment, points to an improved energy level alignment with NPB and, therefore, enhanced hole injection efficiency. We found no significant reactions nor level bending for NPB deposited on standard ITO. In contrast, for acid-treated ITO, reaction of NPB nitrogen with the proton of the dipole layer on the ITO surface is observed. At low NPB coverages, AFM images reveal uniform island growth of NPB on ITO. Further deposition leads to a more complete covering of the ITO surface by NPB layer, corresponding to a laminar growth mode.

Control of the molecular interaction in the emitting layer of organic light-emitting device

The molecular interactions and their effects on the emission properties of organic LED are reviewed. Improvements of the device characteristics are demonstrated in some system with various molecular interactions. Then, it was possible to obtain simultaneously high luminescence efficiency and high charge mobilities by introducing the special molecular interaction in the emitting layers of LED.

Electroluminescent properties of functional p-electron molecular systems

Abstract

Humidity-induced crystallization of tris (8-hydroxyquinoline) aluminum layers in organic light-emitting devices

We report electroluminescence degradation studies of tris (8-hydroxyquinoline) aluminum (Alq3) organic light-emitting devices (OLEDs) under ambient conditions. Alq3 films and organic bilayer anode/naphthyl-substituted benzidine derivative/Alq3/cathode devices are studied via electroluminescence, photoluminescence, polarization microscopy and atomic force microscopy, and via microscopic infrared spectroscopy. Results reveal that humidity induces the formation of crystalline Alq3 structures in originally amorphous films. The same phenomenon is found to occur in OLEDs and causes cathode delamination at the Alq3/cathode interface that results in the formation of black (nonemissive) spots in the devices.