The external coupling efficiency in planar organic light-emitting devices i
s modeled based on a quantum mechanical microvavity theory and measured by
examining both the far-field emission pattern and the edge emission of ligh
t trapped in the glass substrate. The external coupling efficiency is depen
dent upon the thickness of the indium-tin-oxide layer and the refractive in
dex of the substrate. The coupling efficiency ranges from similar to 24% to
similar to 52%, but in general it is much larger than the 18.9% expected f
rom classical ray optics. (C) 2001 American Institute of Physics.