纳米ZnO薄膜对有机电致发光器件性能的影响

由于有机电致发光器件(Organic light-emitting devices,OLEDs)的主动发光、高亮度等优点,在显示和照明领域有极大的应用前景。报道了纳米ZnO薄膜对这种发光器件性能的影响。在普通有机电致发光器件空穴传输层和发光层之间直接蒸镀一层纳米ZnO薄膜,当纳米ZnO薄膜的厚度为1nm时,器件的电流效率可达3.26cd/A,是没有纳米ZnO薄膜同类器件的1.24倍。适当厚度的纳米ZnO薄膜降低了发光层空穴的浓度,提高了电子和空穴的平衡,从而提高了器件的效率。

Organic Light-emitting Devices with Thin Nano-ZnO Film

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 (Alq3) 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/Alq3/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, Alq3, 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/m2 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 Alq3 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.