Investigation of dye-doped red emitting organic electroluminescent devices with metal-mirror microcavity structure

Organic electroluminescent (EL) devices with planar microcavity structure, indium-tin-oxide/Ag∕N,N′-diphenyl-N , N ′-bis(3-methylphenyl)-1,1′-biphenyl-4 , 4′-diamine/tris(8-hydroxyquinoline)-aluminum (AlQ):4-(dicyanomethylene)-2-methyl-6-(p-dimethyl aminostyryl)-4H-pyran/AlQ∕LiF∕Al, were fabricated. The Ag and Al layers acted as not only hole-injection layer and cathode, respectively, but reflective mirrors, resulting in strong microcavity effects, such as spectral narrowing and directional emission. The effects of device parameters on the EL performance were studied in detail and were discussed in terms of conventional microcavity theory. On-axis light magnification with a coefficient (EL enhancement ratio between cavity and noncavity devices) of ∼5 was observed, which was consistent with the theoretical calculation. At the same time, optimized microcavity device with bright pure red emission showed maximum luminance of 5140cd∕m2, peak at 624nm, Commission International de I’Eclairage coordinates of x=0.663 and y=0.336, and high EL efficiency of 1.71cd∕A were obtained.