Surface defects impeded excitons in Alq ₃ 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 (Alq ₃ )/LiF/Al were fabricated on indium tin oxide coated corning glass substrate under various Alq ₃ deposition rates. We demonstrate the significance of deposition rate on the morphology of Alq ₃ layers and subsequently generation of photons in TPD/Alq ₃ hetero junction. The pin holes formed on the surface of Alq ₃ at low deposition rates are responsible for exciton quenching. The device fabricated with the deposition rate of 3.0 */s exhibits the maximum luminescence and maximum current efficiency of 1.02 × 10 ⁴ cd/m ² and ∼5 cd/A, respectively, at 15 V owing to the efficient recombination of excitons in Alq ₃ emissive layer.