Blue Organic Light-Emitting Diodes Fabricated by Using an Enhanced Hole-Blocking Property

Abstract

Blue-emitting organic light-emitting diodes (OLEDs) have fabricated by using a hole-blocking layer, bis(2,4-dimethyl-8-quinolinolato)(triphenylsilanolato)aluminum (III) (24MeSAlq). The device of glass/ITO/2-TNATA (60 nm)/NPB (15 nm)/24MeSAlq (20 nm)/Alq3 (45 nm)/LiF (1 nm)/Al (100 nm) was fabricated by applying a principle confining an exciton recombination zone into a hole-transporting layer, resulting in a maximum electroluminescent peak at 446 nm originating from a 4,4’-bis[N-(1-napthyl)-N-phenyl-amino]-biphenyl (NPB) emissive layer. Among q2AlOR-type aluminum derivatives (q = 8-quinolinolato ligand; Al = aluminum; OR = aryloxy or siloxy ligand), 24MeSAlq with a highest occupied molecular orbital (HOMO) energy level of 6.14 eV exhibits excellent hole-blocking properties compared to bis(2-methyl-8-quinolinolato)(4phenylphenolato)aluminum (III) (BAlq) with a HOMO energy level of 5.88 eV, and it generates deep-blue light efficiently from the NPB layer.