QUANTUM EFFECTS ON ENERGY TRANSPORT IN 2D HETERO-INTERFACES AND LEAD HALIDE PEROVSKITE QUANTUM DOTS

Photovoltaics are leading devices in green energy production. Understanding the fundamental physics behind energy transport in candidate materials for future photovoltaic and optoelectronic devices is necessary to both realize material limitations and improve efficiency. Excitons, which are bound electron-hole pairs, are central to determining how energy propagates throughout semiconductors. Exciton transport is greatly influenced by material dimensionality. In highly ordered quantum dot (QD) systems, electronic coupling between individual QDs can lead to coherent exciton transport, whereas in two-dimensional heterostructures, excitons can form at the interface of a heterojunction, creating charge-transfer excitons.

This dissertation is dedicated to summarizing the studies of exciton transport and behavior in two systems: perovskite QD superlattices and transition metal dichalcogenide (TMDC)/polyacene heterostructures. Chapter 1 provides readers with details on these materials in addition to information on the fundamental concepts (i.e., excitons, phonons, energy transfer) needed to best appreciate further chapters. Chapter 2 summarizes the spectroscopic techniques (photoluminescence and transient absorption spectroscopy and microscopy) used to examine exciton behavior. Next, the effects of disorder and dephasing pathways on the ability of perovskite QDs to coherently couple is investigated through the lens of superradiance in Chapter 3. After this, the temperature-dependent exciton transport within perovskite QD superlattices is imaged with high spatial and temporal resolutions in Chapter 4. The experimental transport data on these superlattices provides evidence for environment-assisted quantum transport, which, until this study, had yet to be realized in solid-state systems. In Chapter 5, attention is switched to verifying the existence and deepening the understanding of the behavior of several spatially separated interlayer excitons in a tungsten disulfide/tetracene heterostructure. Finally, Chapter 6 summarizes the preliminary results obtained through transient absorption spectroscopy on other TMDC/polyacene heterostructures where separation of the triplet pair state is attempted.

It is this author’s hope that this dissertation will not only summarize their graduate work but will also serve as inspiration for others to continue learning and contribute to the advancement of the energy research field.