Improvement Of The Near-UV Electroluminescence Performance Of ZnO/MEH-PPV Heterojunction By Using Interface Modification

ZnO based light emitting diodes have drawn more and more attention due to the unique properties and advantages of ZnO. But the weakness of the emitting light and the difficulties of p-doping have become vital elements, which obviously restrain the development and the wide application of ZnO. In this thesis, we use a simple step to fabricate ZnO nanorods, which is growing vertically on the ITO substrate. We use this ZnO nanorods and MEH-PPV to fabricate light emitting diodes. The improvements of the UV light emitting of the device have been studied.Firstly, we improve the performance of the device by inserting an electron transport layer next to the cathode Al. we use the hydrothermal method to fabricate ZnO nanorods on ITO substrate directly, then MEH-PPV layer is spin-coated on prepared ZnO nanorods. Alq3thin film is deposited on MEH-PPV by thermal vacuum evaporation. The structure of the devices we obtained is as follows: ITO/ZnO/ZnOnanorods/MEH-PPV/Alq3/Al. The thickness of Alq3is10nm,15nm, and20nm, respectively. We find that the appropriate thickness of Alq3is10nm through this experiment. According to the experiment results, a great decrease of the emitting of MEH-PPV and a great increase of emitting of380nm are detected in the device with10nm Alq3. At the same time, the total luminance power is also enhanced from10nW to45nW.Secondly, the cathode modification layer is introduced into the device ITO/ZnO/ZnO nanorods/MEH-PPV/Al. The modification layer is LiF and Cs2CO3respectively. LiF is prepared by thermal vacuum evaporation and Cs2CO3is by spin coating. The fabricated devices are as follows:ITO/ZnO/ZnOnanorods/MEH-PPV/LiF/Al and ITO/ZnO/ZnO nanorods/MEH-PPV/Cs2CO3/Al. Adding LiF obviously solves the difficulty of electron injection, which directly leads the increase of the emitting of380nm. The same has happened to Cs2CO3, which not only improves the proportion of380nm light emitting of all light, but also improves the total light power of the device.Finally, the suitable condition to fabricate ZnO nanorods directly on organic material PEDOT:PSS is discussed. We use prepared ZnO nanorods in this condition and MEH-PPV to fabricate light emitting diodes, and we also discussed the suitable condition of realizing the380nm light emitting of this device.