Ultrafast Relaxation Dynamics of Novel Organic and Inorganic Nanohybrids

Date of Award

6-2024

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Ramakrishna Guda, Ph.D.

Second Advisor

Ekk Sinn, Ph.D.

Third Advisor

Gellert Mezei, Ph.D.

Fourth Advisor

Clement Burns, Ph.D.

Abstract

Optoelectronic materials have been in the forefront of research for the last few decades because of their applications in photovoltaics, light emitting diodes, optical sensors etc. The search for new and efficient materials is ongoing and semiconductor nanomaterials are playing a pivotal role in such endeavors. Since perovskites were used in dye-sensitized solar cells with efficiency reaching 3.8% in 2009, research on perovskites as optoelectronic materials has expanded exponentially. The understanding of exciton relaxation dynamics in perovskite nanomaterials can shed light on their use in optoelectronic devices. All inorganic perovskite nanomaterials in CsPbX3 (X=Br, Cl, and I) have garnered research attention for applications in light emitting displays, sensors etc. On the other hand, organic nanomaterials have contributed significantly to the design and development of cost-effective light harvesting materials. Carbonaceous materials are the pillars of organic nanomaterials and in recent years a new class of carbonaceous materials has emerged in the form of Carbon dots (CDs) that are easy to synthesize and inexpensive. Also, hybrid organic/inorganic nanomaterials are playing an important role as light harvesting materials. For all these materials, the understanding of intrinsic exciton relaxation dynamics, charge carriers and interfacial charge transfer interactions is important. Significant advancements were made in this direction, some of the aspects need immediate attention that include the nature of charge carrier decay in perovskite nanocomposites, origin of PL decay in CDs, thermalized/non-thermalized interfacial charge transfer between perovskite/molecule and perovskite/CD hybrid. The main goal of the research is the design and development of novel materials for optoelectronic devices. The specific research objectives include understanding of charge carrier relaxation in perovskite nanocomposites, excited state decay in CDs, interfacial charge transfer in perovskite/CD nanomaterials. In this dissertation, studies were carried out to achieve the objectives.

Firstly, the research has focused on the excitation relaxation in CsPbBr3 nanocomposites with emphasis on deciphering biexciton decay vs exciton-exciton annihilation. Using the power of femtosecond transient absorption anisotropy measurements, biexciton decay was found to be the main deactivation pathways in CsPbBr3 nanocrystals. In contrast, exciton-exciton annihilation was found to be the main relaxation pathway in CsPbBr3 nanorods. Secondly, the excited state relaxation in pyrene-based, and citric acid-based CDs was studied using femtosecond transient absorption and anisotropy measurements. The studies have revealed that homo-fluorescence resonance energy transfer between the chromophores is the reason behind the excitation-wavelength dependent PL in CDs. Interfacial charge-transfer between perovskite nanocomposites strongly bound to catechol molecules was investigated. The studies have shown ultrafast forward charge transfer and charge recombination between CsPbBr3 and bound catechol derivatives. The dynamics of interfacial charge transfer fell in the inverted region of Marcus theory and a reorganization energy of 0.55 eV indicating adiabatic electron transfer with minimal contribution from solvents. In the case of CsPbBr3/Alizarin, the interfacial charge transfer led to sensitization of triplet state of Alizarin. The dynamics of charge transfer between CsPbBr3 and CDs was studied, and the results have shown up to 40% extraction of charge carriers from non-thermalized states and thermalized state charge-transfer followed Marcus Electron transfer theory.

Access Setting

Dissertation-Abstract Only

Restricted to Campus until

6-1-2034

This document is currently not available here.

Share

COinS