Photogeneration Diffusion and Decay of Charge Carriers in Quantum-Dot Solids

Semiconductor nanocrystals (NCs), which can have a variety of sizes, shapes and chemical compositions, will be a large and important family of future advanced materials.This thesis focuses on colloidal semiconductor NC solids, also called quantum-dot (QD) solids, which are promising materials for many applications, such as photo-detectors, field-effect transistors, solar cells, light-emitting diodes, and lasers. The thesis presents studies on the charge carrier properties of PbSe QD solids, going through the charge carrier photogeneration, thermalization, diffusion and decay, which together are the ``life and fate'' of the charge carriers. Diverse tools have been utilized to reveal the whole picture of the ``life and fate''. The most important ones are: femtosecond transient absorption spectroscopy (TA) (Chapter 2, 3, 4), picosecond Terahertz spectroscopy (THz) (Chapter 2), the nanosecond time-resolved microwave conductivity technique (TRMC) (Chapter 2-5), and Monte Carlo simulations (Chapter 4)