Thickness dependent emission color of organic white light-emitting devices

Abstract

We demonstrate molecular organic white light-emitting devices (LEDs), using vacuum-deposited thin films of N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′- diamine (NPB) as the hole-transporting layer, 1,6-bis(2-hydroxyphenyl)pyridine boron complex ((dppy)BF) as the emitting layer, tris-(8-hydroxyquinoline)aluminum (Alq) doped with 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as the red-emitting layer. The chromaticity of the devices can be tuned by varying the thickness of (dppy)BF and doped Alq layers. The Commission Internationale De L'Eclairage (CIE) coordinates of emitted light vary from (0.31,0.335) to (0.32,0.345) when forward voltages change from 10 to 20 V, which are just adjacent to the white-light equi-energy point (0.33,0.33). The brightness and luminous efficiency are 150 cd/m2 and 0.3 lm/W at 12 V, respectively.