Surface Modification Influence On The Properties Of Electroluminescent Devices With Zn-based Nanomaterials

The optoelectronic devices with Zinc-based nanomaterials (such as ZnO, ZnS etc.) as active layer have received extensive attentions because of their wide and direct band gap structure. The more applications are also being developed in the field of LED, laser and infrared detector, photochemical catalyst and light sensors. In this paper, the optical and electrical properties of LED devices based on ZnO nanorods and ZnS quantum dots have been studied. The successive discussion on optical-electrical characteristics for devices including ZnO nanorods/organic LEDs, the all inorganic ZnO nanorods LEDs and the ZnS:Mn quantum dot LEDs are performed detailly. The main contents are as follows:1) ZnO nanorods are synthesized by a simple aqueous chemical growth method on ITO substrate. The organic/inorganic hybrid devices, with the structure of ITO/ZnO/ZnO nanorods/polymer/Al, are obtained by the. spin coating process. The results of SEM and XRD show a high vertical orientation of ZnO nanorods arrays and good crystallization under two different precursors. Near ultraviolet emission from band edge at377nm and the wide visible emission of the ZnO nanorods are observed from the PL and EL spectra. With the I-V curves and energy structure, the mechanism for devices based on hybrid of ZnO nanorods and polymer is discussed. The difference in turn-on voltage and working current for PMMA and PVK is attributed to the dissimilar molecular structure in which PVK has a chain structure and PMMA a reticular structure. In addition, the modification of polymer on the surface of ZnO nanorods avoided the leakage phenomenon for electron devces.2) The all-inorganic LEDs, with the structure of ITO/ZnO/ZnO nanorods/SiO2/Al, are obtained with various amount of amorphous SiO2by different spin-coating speed. The dependence of absorbance spectra and energy dispersive spectra (EDS) on the modification amount of SiO2shows the gradual increase when the casting speed is from3000rpm to500rpm. The electroluminescent (EL) spectra of device, influenced by the amorphous SiO2, are measured and compared. The discussion based on PL spectra and the energy level diagram suggests that, beside of surface passivation of ZnO nanorods by SiO2, the high barrier between ZnO and SiO2induced electron accumulation and suppress non-radiative recombination at ZnO layer. And the silica on the surface of ZnO nanorods helps to improve the electron density and then the recombination rate at the higher levels of ZnO.3) The hybrid organic/inorganic WLEDs, with the structure of ITO/PVK:TPD/ZnS: Mn@SiO2/Al, are fabricated. The EL spectrum for hybrid device shows a wide band emission which is composed by the emission of TPD (420nm), PVK (520nm) and the ZnS:Mn (590nm). With comparison to the all-inorganic LEDs which the device structure is ITO/ZnS:Mn@SiO2/Al, the EL mechanism is discussed. The chromaticity coordinates of device approached to white emission (0.34,0.33) under the forward bias of6V, which is provide an ideal white light.