Fabrication and characterization of quantum-confined optoelectronic devices based on CdSe nanocrystals

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2002.Includes bibliographical references.Colloidal semiconductor quantum dots (QDs), or nanocrystals (NCs), are the subject of intense research for their novel size dependent optical and electronic properties. Since the development of synthetic methods to produce cadmium selenide (CdSe) QDs with very controlled size-distributions and high crystalline quality, their potential applications in a variety of fields are being extensively explored. In this thesis, I present a simple chemical approach to greatly enhance not only the quantum yields of the CdSe and (CdSe)ZnS NCs, but also their viability in commercial applications such as LEDs, optoelectronics and biological tagging. Then I will describe our recent success in fabricating a solid-state NC capacitor. We can inject charges into these NCs with this device structure and control their fluorescence and absorption behavior. A green emitting LED with the CdSe NCs as the emissive material and a semiconducting polymer as the hole transport material is studied next. This is the first working device from which green electroluminescence of CdSe NCs is observed. Finally, I will describe results on the first efficient hybrid molecular organics/NCs LED. This device is a double heterojunction structure with a single monolayer of NCs sandwiched between 2 different molecular organics. This new device structure exhibits the highest reported quantum efficiency of 0.4%.by Wing-Keung Woo.Ph.D