Surface defects impeded excitons in Alq3 based hetero junction OLEDs

Hetero junction organic light emitting device consists of N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD)/tris-(8-hydroxyquinoline)aluminum (Alq3)/LiF/Al were fabricated on indium tin oxide coated corning glass substrate under various Alq3 deposition rates. We demonstrate the significance of deposition rate on the morphology of Alq3 layers and subsequently generation of photons in TPD/Alq3 hetero junction. The pin holes formed on the surface of Alq3 at low deposition rates are responsible for exciton quenching. The device fabricated with the deposition rate of 3.0 Å/s exhibits the maximum luminescence and maximum current efficiency of 1.02 × 104 cd/m2 and ∼5 cd/A, respectively, at 15 V owing to the efficient recombination of excitons in Alq3 emissive layer.