Synthesis of cd-free quantum dots and their application for optoelectronic devices

Abstract

Global warming is caused by greenhouse gases from the burning of fossil fuels like oil, coal, and gas. This collapse of our climate threatens the survival of all human beings. Therefore, there are growing demands for development of energy-saving and renewable energy materials/devices. Among them, LEDs and solar cells have drawn a lot of attention over the past few years. Semiconductor quantum dot (QD) can be promising candidate in the energy-related industry. QDs are nanoparticles that can tune the absorption and emission in the ultraviolet, visible, and infrared region. They have high quantum yield and excellent color purity, which are advantages for light source. In solar cells, they have high optical extinction coefficient, large dipole moment, and property of multiple exciton generation. There has been extensive research on Cd or Pb chalcogenide QDs showing their excellent optical properties. However, the use of these QDs for optoelectronic devices is becoming more problematic because of the presence of Cd or Pb, which could cause serious health problems and is currently restricted by the agreement of the Restriction of Hazardous Substances. In addition, traditional batch processes are of limited utility for the synthesis of high quality QDs on a larger scale because of limited heat control and lack of efficient mixing. In this thesis, we report the synthesis of an Eu complex-capped ZnSe QD, which is a color-tunable, organic??inorganic hybrid material emitting white light. Secondly, we demonstrated the successful one-pot synthesis of ZnSe/ZnS core/shell QDs using a cyclic olefin copolymer (COC)-based microfluidic system. Finally, we fabricated QD LEDs and QD solar cells by using InP based QDs and/or QD-carbon nanotube (CNT) composites. In chapter 3, surface-functionalized hybrid ZnSe QDs emitting white light were introduced. The conventional fabrication of white LEDs containing either UV or blue LED which is dispensed by various light-emitting QDs can be s...