White light-emitting devices with a single emitting layer based on bisindolylmaleimide fluorophores

Abstract

A series of bisindolylmaleimide dyes (1–3) were synthesized and they exhibited intensive orange to red color luminance deriving from charge transfer transitions. Highly efficient light-emitting devices were fabricated using these materials as emitters by doping 1% in a tris(8-hydroxyquinolinato)aluminium (Alq₃) host, which performed in a quantum efficiency of ∼4% with a maximal intensity >40 000 cd/m². Broad band white emission can be produced by combining their reddish color with another blue emitter. While doped in 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB) in suitable concentrations, dual emission was obtained from a single layer. The device with configuration ITO/PEDOT:PSS/dye 1 (1%):NPB/TPBI/LiF/Al yielded white light with maximum luminance efficiency of 6.6 cd/A, power efficiency of 6.4 lm/W and quantum efficiency of 2.6%, where PEDOT:PSS is poly(ethylenedioxythiophene):poly(styrenesulfonic acid), and TPBI is 2,2′,2″-(1,3,5-benzentriyl)tris(1-phenyl-1H-benzimidazole). This device can be turned on at a low voltage (<3 V) and emits a white color with CIE coordinate (0.32, 0.34), which stays invariant over a wide range of applied voltage.