Organic light-emitting devices (OLEDs) have various advantageous features

such as self-emission

high luminous efficiency

full-colour capability

wide viewing angle

high contrast

low power consumption

low weight

potentially large area colour displays and flexibility. So

they have attracted considerable interest due to their promising applications in flat-panel displays. Here

the effect of ZnO nanolayer on the efficiency of OLED is reported. ZnO nanolayer was introduced between 8-hydroxyquinoline aluminum (Alq

3

) and N

N-bis-(1-naphthyl)-N

N-diphenyl-1

1-biphenyl-4

4-diamine (NPB) layers

and their influence on the device performance was investigated. When the 1.0 nm ZnO film is inserted

for an unoptimized device composed of indium-tin oxide (ITO)/NPB/ZnO/Alq

3

/LiF/Al

the current efficiency is as high as 3.26 cd·A

-1

. It is much higher than that of conventional device. The mechanism of performance enhancement was discussed. For the fabrication of the OLEDs

ITO (sheet resistance 30 Ω/□) glass

thoroughly cleaned was used. The routine cleaning procedures include ultrasonic agitation in acetone

ethanol

rinsing in de-ionized water

and isopropyl alcohol. After the oxygen plasma treatment in vacuum chamber

the substrates were loaded into a vacuum chamber with a base pressure of 4.0×10

-4

Pa. LiF

NPB

ZnO

Alq

3

and Al electrode were thermally deposited without breaking the vacuum

respectively. The deposition rate and film thickness were measured by a quartz oscillator connected to a frequency meter near the substrates during the deposition. In this study

we define the voltage as the operating voltage when emitted light is first detected. The level of light first resolved is around 1 cd/m

2

in our experimental setup. The current-voltage characteristics reported here were all measured in the forward bias voltage mode. In conclusion

it was found that the 1 nm thick ZnO layer can greatly improve the performance of the Alq

3

based organic light-emitting device. The improved efficiency of the device could be due to the ultrathin ZnO layer acting as the decreased holes injection into the emissive layer

which would made the number of electrons and holes injected into the emitter layer to be balanced.