Synthesis, Ion Exchange, and Properties of New Semiconductor Nanostructures
Advances in the synthetic control of semiconductor nanostructures and material properties offers many opportunities to enable new technologies. This is especially true for advances in the areas of photovoltaics, light emitting diodes, photodetectors, transistors, miniaturized lasers, and thermoelectrics. In this work, I demonstrate the synthesis and properties of several novel nanoscale morphologies composed of copper sulfide, cadmium sulfide, and halide perovskite, which can be useful for these applications. Here, I demonstrate the first synthesis of Cu2S-CdS core-shell nanowires by reverse cation exchange, and I explore the evolution of the epitaxial interface during the cation exchange. In addition, I demonstrate the synthesis and photovoltaic properties of core-shell CdS-Cu2S nanorod arrays with power conversion efficiencies approaching 4%. I also demonstrate the first bottom-up synthesis of CH3NH3PbBr3 nanorod arrays and the first example of morphology-conserving anion exchange to CH3NH3PbI3. As a demonstration of this, I created and characterized the first halide perovskite nanorod array light emitting diodes. Furthermore, using the first example of ultrathin halide perovskites, I demonstrate the unexpected changes in the structural and optical properties of layered halide perovskites as they approach ultrathin thicknesses. Finally, I synthesized the first example of all-inorganic, lead-free perovskite CsSnI3, which is shown to possess strong photoluminescence at 1.3 eV, metallic electrical conductivity, and ultralow thermal conductivity. These research directions all contribute towards the ultimate goal of providing new nanostructured materials to enable new technologies and innovations, which might also lead to new energy generating and energy saving applications.