Quinacridone sub-monolayer as efficient emitter in OLEDs

Efficient electroluminescence (EL) was obtained in organic light-emitting devices (OLEDs) using a Quinacridone (QAD) sub-monolayer as emitter, which was inserted in a narrow excitons formation Alq3 layer. For the structure-optimized devices, efficient QAD emission almost without Alq3 EL was observed, and a highest efficiency of 7.2 cd/A was attained by inserting 0.02-nm-thick QAD layer in the middle of 10-nm-thick Alq3 layer which neighbored a blocking layer 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP). The performance improvement was attributed to the application of the narrow excitons formation zone, in which both electrons and holes were confined, and resulted in efficient collision capture for the excitons formation. Confinement of excitons induces enhanced energy transfer from Alq3 to QAD and weak emission from the Alq3.