The red organic LEDs with high brightness and good color purity are necessary for the achievement of full-color emission displays.Commonly

the red OLEDs were made by doping the DCJTB into the Alq

3

host due to its stability and charge-transporting ability.But this doped system showed a contrary phenomenon of low efficiency(at high concentrations of DCJTB) or poor color purity(at low concentrations of DCJTB).Meanwhile

the efficiency of these devices declined rapidly after it reached the maximum efficiency point with the applied voltage increasing.Although intensive research has been made in recent years

the performance of red devices is not satisfactory either the luminance efficiencies or the color purity.In this paper

we fabricated organic EL devices with double emitting zone in order to obtain the efficiency independent on the applied vol-tage and together with good color purity.The saturated red organic light-emitting diode(OLED) has been realized by doping an emitting material in the hole-transporting layer(HTL)and electron-transporting layer(ETL) to form double emitting zone.The red dopant

DCJTB

was doped into the NPB layer and Alq

3

layer

which both act as the emitting layer.The optimal device

with a structure of ITO/CuPc/NPB/NPB:DCJTB/Alq

3

:DCJTB/Alq

3

/LiF/Al

showed a good performance of the current efficiency being relatively independent of the drive voltage in a wide range from 8V to 20V(only reduced by 4%)and the chromaticity coordinates changed from 8V(

x

=0.6287

y

=0.3663)to 20V(

x

=0.6075

y

=0.3841)

and the devices maintain a pure red emission.That may be helpful to ameliorate the lifetime of the organic electroluminescence(EL) devices and adjust the gray-scale for the future full-color display panel.