Microcavity Effect in Compliance with Interference of Light in Alq₃ Based Top-Emission Organic Light-Emitting Diodes

Abstract

Since top-emission organic light-emitting diodes have a structure of microcavity, there is a change in emission spectrum compared to that of noncavity such as a full width at half maximum and peak wavelength of the spectrum. Optical properties of top-emission organic light-emitting diodes were studied depending on an organic layer thickness and view angle. A structure of the manufactured device was Al(100 nm)/TPD/Alq₃/LiF(0.5 nm)/Al(2 nm)/Ag(30 nm). An Al(100 nm) and LiF(0.5 nm)/Al(2 nm)/Ag(30 nm) were used as an anode and semitransparent cathode, respectively. A thickness of hole injection layer of N,N′-diphenyl-N,N′-bis(3-metylphenyl)-1,1-biphenyl-4,4′-diamine (TPD) was varied from 40 nm to 70 nm, and that of an emission layer of tris(8-hydroxyquinoline) aluminum(III) (Alq₃) was varied from 60 nm to 110 nm. At each device, a thickness ratio of TPD and Alq₃ layer was kept to be about 2:3. It was observed that the emission spectrum of top-emission organic light-emitting diodes shows a microcavity effect when the organic layer thickness and view angle were varied. This microcavity effect of the device was analyzed in terms of theoretical interpretation based on an interference of light. Through these analyses, we were able to understand a shift of peak wavelength in spectrum, and deduce a refractive index and a thickness of organic layer. These deduced values are in agreement with known values.

Keywords:

• Alq₃
• interference
• microcavity
• spectrum
• top emission