Electroluminescence in semiconductor nanocrystals

Colloidal semiconductor nanocrystals having emission colors, electron affinities, and ionization potentials that vary with nanocrystal size can be produced using a single synthetic route. In addition, they can be deposited as monolayers and thin films capable of charge transport. These attributes make them ideal for use in a solid state electroluminescent (EL) device.; In this thesis, the preparation and characterization of CdSe/CdS core-shell nanocrystals having high structural quality is reported. Compared to semiconductor nanocrystals of a single material, these core-shell nanocrystals possess excellent room temperature photoluminescence quantum yields and photo-oxidative stability.; This thesis reports on the fabrication and testing of bilayer light emitting diodes consisting of a layer of poly(p-phenylenevinylene) (PPV) and a layer of semiconductor nanocrystals (either CdSe-only or CdSe/CdS) sandwiched between two electrodes. The devices show either nanocrystal-only EL or a combination of nanocrystal and PPV EL, depending on the nanocrystal layer thickness. The nanocrystal EL is dependent on the nanocrystal size. For certain nanocrystal layer thicknesses, a voltage dependent color is observed. Devices made with CdSe/CdS nanocrystal show significant improvements in efficiency and lifetime of operation compared to devices made with CdSe-only nanocrystals.