Controlling the carrier recombination zone for improved color stability in a two-dopant fluorophore/phosphor white organic light-emitting diode

Abstract

A white organic light-emitting diode (WOLED) is produced upon systematic introduction of deep-blue fluorescence from 4,4′-bis(9-ethyl-3-carbazovinylene)-1,1′-biphenyl to broad-band yellow phosphorescence from bis[3,5-bis(2-pyridyl)-1,2,4-triazolato]platinum(II) in the common host 4,4′-bis(carbazol-9-yl)biphenyl. The carrier recombination zone is first identified upon investigating alternative device structures, then optimized by varying the thickness of the electron-transport layer. The WOLED exhibits striking stability of color and efficiency, as manifest by parameters at high brightness of 1000 cd/m2 sustaining 94%–122% their values at 50 cd/m2.