Synthesis Of CdSe Core/Shell Nanocrystals And Its Interaction With Organic Carrier Transporting Materials

Quantum dots (QDs), are being applied to fabricate hybrid inorganic/organic light-emitting diodes (LEDs) because the QDs exhibit size-tunable photoluminescence (PL), narrow emission line width, high PL quantum yield, superior photochemical stability, and flexible solution processibility. The performance of the QD-based devices is strongly dependent on the structure and the surface properties of the QDs. The effect of organic molecules on the PL properties of CdSe QDs has been widely studied to understand the nature of the QD surface and charge/energy transfer processes between QDs and the organic molecules for further improving the device performance.In the present work, we developed a simple method for synthesizing multishell quantum dots (QDs). The method adopted the one step injection of zinc precursor into the crude solution of the CdSe reaction system to obtain CdSe/ZnSe core/shell QDs, and then, ZnS shell epitaxially grew on the CdSe/ZnSe surface to form CdSe/ZnSe/ZnS core/shell/shell structured QDs. In comparison with previous reported synthesizing method, our method needs less processes, it can effectively simplified the experimental operation, shorten the experimental cycle, and reduces waste of the materials. The resulted CdSe/ZnSe/ZnS QDs are with a high quantum yield.Different CdSe core/shell QDs were added in chloroform with different concentrations of hole transporting materials (HTM), generally used in QD-LEDs. We find that the PL quenching efficiency of the QDs is strongly dependent on the structure of the shells and the energy mismatch between the HOMO level of the HTMs and the valence band of the QDs. The larger the energy mismatch, the lower the quenching concentration of the QDs, and the stronger the charge transfer from QDs to HTMs.Energy transfer from organic electic transporting materials to the CdSe/CdS/ZnS QDs were also studied in this thesis. The PL in Alq₃:CdSe/CdS/ZnS QD mixed films is governed by energy transfer from Alq₃ to QDs. The transfer is characterized by a Forster radius of 5.23 nm. The lifetime of Alq₃ gets shorter and the efficiency of energy transfer gets larger with increasing of QD concentration. The existence of energy transfer from TPBI to QDs in TPBI: CdSe/CdS/ZnS QD mixed film was also verified with excitation spectra.