Synthesis Of ZnO Quantum Dots And Applications In Organic Light Emitting Diodes Based On MEH-PPV

The preparation of ZnO quantum dots (QDs) with modified chemical solution method was studied, and ZnO QDs were characterized with X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), Absorption Spectrum (Abs) and Photoluminescence Spectrum (PL) methods. The size of ZnO QDs was uniform (the diameter of ZnO QDs is approximately4.83nm). The ZnO QDs were randomly distributed in the ethyl alcohol; the blue shift of optical absorption edge (from370nm to359nm) and photoluminescence peak (from387nm to approximately377nm) was observed because of a so-called quantum size effect.The stability of ZnO QDs was studied. Different dispersion degree of ZnO QDs distributed in the ethyl alcohol were prepared by changing the density of ZnO QDs (from1.6mol/L to0.05mol/L). Photoluminescence peaks from381nm to371nm were observed, the cause of which was researched. Only nearly ultraviolet photoluminescence peaks were observed, which came from the excitonic luminescence of ZnO QDs, proving that surface defect and impurity defect were less in ZnO QDs. The ageing of ZnO QDs was also studied. Ageing under different conditions (room temperature25℃ageing for30days,0℃ageing for30days and ZnO QDs just prepared), the reunion, topography and PL peaks of ZnO QDs would be different. The reunion mechanism and the cause of it were discussed.ZnO QDs have good electronic transmission characteristics because of their Coulomb blockade effect. Therefore, ZnO QDs applied as Electron Transport Layer (ETL) to balance of the charge carriers in inorganic-organic light-emitting diodes (LEDs) and to improve the luminous efficiency of MEH-PPV was studied. The device started luminising at voltage3.0V,(The current is from8mA to14mA at voltage8.0V; the light power is from112nw to147nw at voltage8.0V); The EL peak is590nm.Theoretically, nearly ultraviolet emission (blue shift compared to that of ZnO bulk materials) could be observed, based on the quantum blue shift effect of ZnO QDs. Quantum-dot-based LEDs are characterized by pure and saturated emission colors (Halfpeak breadth is more or less40nm) with narrow bandwidth, and their emission wavelength is easily tuned by changing the size of the quantum dots. Therefore, we tried to dope ZnO QDs into MEH-PPV as Emitting Layer (EL) in order to get the nearly ultraviolet emission of ZnO QDs, but failed because of quenching, which came from the surface defect (such as dangling bonds on the surface) of ZnO QDs.