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 Förster energy transfer processes. In many cases this energy transfer process can be very efficient, leading to fairly large Förster 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 Förster radius for TPP in Alq 3 (33 Å). 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.