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theses

Global energy consumption has escalated dramatically with continuing consumption and population increase trends. It is one of the biggest challenge in the world to satisfy growing energy demand in an environmentally-benign manner. Solar cells have attracted a significant amount of attention because of its inexpensive, clean and sustainable renewable energy source nature. Although great progress has been made in solar cells, there are a lot of challenges such as high manufacturing cost, loss of material for crystal silicon and low efficiency. In addition, compared to traditional incandescent, energy-efficient lightbulbs, such as compact fluorescent lamps (CFLs) and light-emitting diodes (LEDs), save about 25% - 80% energy with 3 – 25 times longer lifetime. While rare-earth element (REE) based phosphors currently dominate the lighting market, developing low-cost, high-performance and REE free phosphors has becoming increasingly important, due to the potential cost and supply risks of REEs, as well as their negative impact on the environment and human health.
In this thesis I describe the design and synthesis of a family of high-performance inorganic-organic hybrid phosphor materials composed of extended and robust one-, two- and three-dimensional networks. Following a bottom-up solution-based synthetic approach, these structures are constructed by connecting highly emissive Cu4I4 cubic clusters via carefully selected ligands that form strong Cu-N bonds. They emit intensive yellow-orange light with high luminescence quantum efficiency, coupled with large Stokes shift which greatly reduces self-absorption. They also demonstrate exceptionally high framework- and photo-stability, comparable to those of commercial phosphors.
As a continuing effort, I have designed a unique type of multiple-stranded one-dimensional (1D) structures as robust and efficient lighting phosphors. Following a systematic ligand design strategy, these structures are constructed by forming multiple coordination bonds between copper iodide based clusters (e.g. dimer, tetramer and hexamer) and strong-binding bidentate organic ligands which lead to extended 1D chains of high stability. The multiple-stranded chain structures display significant improvements in thermal stability, largely attributed to the multi-dentate nature and enhanced Cu-N bonding. The luminescence mechanism of these compounds are studied by temperature dependent photoluminescence experiments. High internal quantum yields (IQYs) are achieved for these compounds under blue excitation, marking one of the highest values reported so far for crystalline inorganic-organic hybrid yellow phosphors.
I have also developed a series of new copper iodide based hybrid compounds with tunable narrow-bandgaps. Large single crystals are grown and used incharge transport measurements. They exhibit low state trap density on the order of 1010 per cubic centimetre as well as long carrier diffusion length. The high water stability coupled with with good conductivity making these materails a promising candidate for potential optoelectronic applications.

ETD_9538

Ph.D.

Includes bibliographical references

by Yang Fang

doi:10.7282/t3-5v1f-j776

ETD doctoral

The author owns the copyright to this work.