Comparison of electron transporting layer in white OLED with a double emissive layer structure

White organic light-emitting devices consisting of a non-doped ultrathin orange emissive layer (EML) and a doped blue EML were fabricated. The effect of varying electron transporting layers on device performance was studied, while 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, 4,7-diphenyl-1,10-phenanthroline, tris(8-hydroxy-quinolinato)aluminum and 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene (TPBi) were employed, respectively. The results showed that by comparing four kinds of ETLs, the TPBi device exhibited a current efficiency of 20.9 cd/A at a current density of 10 mA/cm2 and a maximum external quantum efficiency of 10.0%, while stable white emission with Commission Internationale de l’Eclairage coordinates of (0.39, 0.43) were obtained, attributing to efficient charge transportation and exciton confinement.

► Reduced efficiency roll-off was obtained by using ultrathin emissive layer.
► Stable white emission was obtained using TPBi as the electron transporting layer.
► Stable color coordinates were obtained without an extra hole/exciton blocking layer.
► The recombination zone is dependent to the choice of electron transporting layer.