(The) synthesis of CdSe nanoparticles and its application to polymer Light-Emitting diodes

Abstract

Since most common organic semiconductors are better suited to transport positive charges, electrons and holes usually recombine in the immediate vicinity of cathode of Light-Emitting diodes. As consequence, the life times and efficiencies of corresponding diodes are limited. There were previous studies of modifying the conjugated polymer using inorganic nanomaterial such as $SiO_2$, clay. But these materials are electronically inactive, so LEDs (light emitting devices) require high working voltage. Here we demonstrate a hybrid light emitting diode that combines the poly[2-methoxy-5-(21-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and semiconductor nanoparticle (CdSe). Chapter 1 described the optical property of the CdSe nanoparticles synthesized by the inverse micelle method. The nano-sized CdSe particles had been successfully produced and the size distribution could be controlled. The most influential factors in size control are the ratio of surfactant, water and reaction time. Structures and optical properties of the CdSe nanoparticles are characterized by TEM, UV-vis absorbance, and photoluminescence (PL) spectra of CdSe nanoparticles. Transmission electron microscope (TEM) images demonstrated the monodispersity of CdSe nanoparticles. The surface of the CdSe nanoparticles was treated to be organic with thiol as an organic modifier. The solubility in organic solvent and the photoluminescence (PL) properties could be enhanced through it. In chapter 2, the energy barrier between cathode (Al) and emitting layer (MEH-PPV) can be reduced by using CdSe nanoparticles because of the electron affinity of CdSe. It enable active device by improving the electron affinity of emitting layer. Optimizations of concentration and $2^{nd}$ order structure of CdSe nanoparticles enhance the power efficiency and the luminescence intensity at remarkably low working voltage in device. The optimized EL device using CdSe nanoparticles achieves about 10-fold improvement of the ...