Perovskite materials are currently being explored as a candidate for a wide variety of optoelectronic applications with a focus on active materials for solar cell and an array of lighting applications. To optimize perovskites for optoelectronic applications, a myriad synthetic and processing techniques are used to overcome limitations in the raw materials. Presently, perovskite materials have demonstrated vast improvements as candidates for solar cell and lighting applications, though the fundamental photophysical characteristics resulting from the rapid succession of synthetic developments require further investigation. Further comprehension of the basic photophysical processes being altered by synthetic and processing changes must be achieved to continue the advancement of perovskite materials. Here, we employ imaging and molecular spectroscopy techniques to explore photophysical changes brought on by synthetic modifications to perovskite materials. We hypothesized that the excited state lifetimes could be used as an indicator to probe the stability of perovskite materials, which was investigated for encapsulated perovskite samples. For 0D nanoparticles an improvement was observed for average photoluminescence lifetimes for and overall structural order with reduced Urbach energy values for encapsulated samples. These findings indicate a surface defect passivation effect from the polymer matrix and imply the emissive nature of these materials proceeds by either bimolecular or trap-assisted recombination events. It was also hypothesized that 1D encapsulated nanorod structures, when mechanically aligned, were capable of emitting polarized light. In addition to emitting polarized light (P=0.4), the encapsulated nanorods were found to display similar photophysical pathways for their emissive processes to that of the encapsulated 0D nanoparticles. Finally, we hypothesized by further reducing 2D Ruddlesden-Popper hybrid perovskite films to quantum dots and nanoplatelets would further increase already prominent quantum confinement effects. The 2D Ruddlesden-Popper perovskite quantum dots and nanoplatelets show strong absorption and emission in the UV region as well as short average photoluminescence decay lifetimes. The outcome of these optical properties can be attributed to the strong quantum and dielectric confinement brought on by the unique quantum well structure adopted by 2D perovskite materials, specifically lattice vibration effects (exciton-polaron interactions) and a mixed layered material (n = 2 or 3). These findings indicate three possible mechanistic emissive processes in these 2D Ruddlesden-Popper perovskites: free exciton, intrinsically trapped, and defect trapped recombination. The results obtained in these studies demonstrate alterations in fundamental photophysical processes as perovskite materials are tailored for various optoelectronic applications.
Doctor of Philosophy (Ph.D.)
College of Sciences
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Towers, Andrew, "Composition, Encapsulation, and Dimensionality: A Study of the Photophysics Brought on by Synthetic Changes in Perovskite Materials" (2020). Electronic Theses and Dissertations, 2020-. 459.