Andrei Shoustikov

Bright, saturated, red-to-yellow organic light-emitting devices based on polarization-induced spectral shifts

We demonstrate red, orange, and yellow organic light-emitting devices (OLED) with the electroluminescent layer consisting of aluminum tris(8-hydroxyquinoline) (Alq3) doped with laser dye DCM2, with the emission color dependent on the concentration of DCM2. A peak emission wavelength shift of up to 50 nm is found to be due to strong polarization effects. For red and yellow–orange OLEDs, a maximum luminance of 1400 cd/m2 and 15200 cd/m2 is measured, with a luminance of 100 cd/m2 attained at 100 mA/cm2 (14 V) and 10 mA/cm2 (12 V), respectively. The current versus voltage dependencies of these devices are consistent with trap-limited conduction, unaffected by the presence of DCM2.

Electroluminescence color tuning by dye doping in organic light-emitting diodes

Doping a small amount of a fluorescent dye into an organic light-emitting diodes (OLEDs) can lead to significant changes in the color of luminescence and an improvement in the device properties (e.g,, quantum efficiency, lifetime, etc.). The process of energy transfer from the OLED material to the dye in these devices may involve several different processes, including carrier trapping as well as Forster and Dexter energy transfer reactions. The important parameters for each of these processes are discussed. The color purity and chromaticities of a wide range of different dye-doped OLEDs are reviewed.

Orange and red organic light-emitting devices using aluminum tris(5-hydroxyquinoxaline)

Abstract Energy transfer in dye-doped organic light-emitting diodes (OLEDs) often occurs by Forster energy transfer processes. In many cases this energy transfer process can be very efficient, leading to fairly large Forster radii. We have recently shown that saturated red emission can be achieved by doping tetraphenylporphine (TPP) into aluminum tris(8-hydroxyquinolate) (Alq 3 ) in an ITO/TPD/Alq 3 /Mg-Ag device (TPD = N,N ′-diphenyl- N,N ′-bis(3-methylphenyl)-1,1′biphenyl-4,4′ diamine; ITO = indium-tin oxide). Predominant red emission is observed even at very low doping levels, as expected for the large Forster radius for TPP in Alq 3 (33 A). In order to increase the degree of overlap between the dopant absorption for red fluorescent dyes and the host emission we prepared a strongly red-shifted analog of Alq 3 , i.e. aluminum tris(8-hydroxyquinoxalate) (Alx 3 ). The photoluminescent efficiency for Alx 3 is significantly lower than that of Alq 3 , leading to a significant decrease in the electroluminescent quantum yield for Alx 3 -based OLEDs relative to Alq 3 -based devices. We have examined the doping of several dyes into Alx 3 , giving red and orange OLEDs.

TiN as an Anode Material for Organic Light-Emitting Diodes**

By VadimAdamovich, Andrei Shoustikov,and MarkE. Thompson*Organic light-emitting diodes (OLEDs) are currently re-ceiving a great deal of attention, both academically andcommercially. These devices have promise in applicationsranging from low information content alphanumeric dis-plays, to high resolution, large area flat panel displays. Themost common OLED structure consists of a substrate coat-ed with a transparent conductor (indium tin oxide, ITO)coated with a thin film of organic material(s), followed by avapor deposited metal cathode. When a potential is appliedto the device, holes are injected into the organic material(s)from the ITO electrode and electrons from the metal cath-ode. The holes and electrons recombine in the organic ma-terial, giving excitons, which radiatively relax to give offlight. The efficiency of the device is best if multiple organiclayers are used, i.e. separate hole and electron transportinglayers.The choice of anode material for OLEDs is based on sev-eral criteria. The anode in a conventional OLED must havegood optical transparency, good electrical conductivity andchemical stability, and a work function that lies near theHOMO levels of the organic materials to which it will in-ject holes. ITO fits these criteria and is the most widelyused anode material in OLEDs. ITO films combine hightransparency (» 90%) with low resistivity (1 · 10