Abstract
We have investigated emissive interface states in fabricated indium–tin-oxide (ITO)/N,N'-di-1-naphthyl-N,N'-diphenyl-1,1'-biphenyl-4,4'diamine (α-NPD)/tris(8-hydroxyquinoline) aluminum (Alq3)/LiF/Al organic light-emitting diodes (OLEDs) by modified deep-level optical spectroscopy (DLOS). DLOS after hole injection into the OLEDs revealed a discrete trap level located at ∼1.77 eV below the conduction band of Alq3 in the emissive interface region, in addition to the band-to-band transitions of charge carriers from α-NPD to Alq3. This pronounced level can be activated as an efficient recombination center of the charge carriers. Also, this trap level was extensively distributed to a lower energy with increasing hole injection rate. Therefore, this level is probably attributable to intrinsic trap states at the α-NPD/Alq3 emissive interface. Thus, DLOS has been proven to be a powerful tool for the characterization of emissive interface states in the OLEDs.
Published Version
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