Enhancement of the efficiency and the color stabilization in green organic light-emitting devices with multiple heterostructures acting as a hole transport layer

The electrical and the optical properties of organic light-emitting devices (OLEDs), with and without multiple heterostructures consisting of N, N-bis-(1-naphthyl)-N, N-diphenyl-1,1-biphenyl-4,4-diamine (NPB)/5,6,11,12-tetraphenylnaphthacene (rubrene) acting as a hole transport layer (HTL), were investigated. The OLEDs with 3 periods of NPB/mixed rubrene:NPB multiple heterostructures acting as an HTL showed the highest luminances and efficiencies. While the electroluminescence (EL) peak corresponding to the rubrene layer did not appear for the OLEDs with 3 periods of NPB/mixed rubrene:NPB multiple heterostructures, only the EL peak related to the tris (8-hydroxyquinoline) aluminum layer was observed. The Commission Internationale de l'Eclairage chromaticity coordinates of the OLEDs with 3 periods of NPB/mixed rubrene:NPB multiple heterostructures at 14 V were (0.321, 0.531), indicative of a deep stabilized green color.