Toward data-rich approaches to understanding colloidal semiconductor nanocrystals and quantum-dot LEDs

Keating, Logan P.

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https://hdl.handle.net/2142/124703 Copy

Description

Title

Toward data-rich approaches to understanding colloidal semiconductor nanocrystals and quantum-dot LEDs

Author(s)

Keating, Logan P.

Issue Date

2024-04-26

Director of Research (if dissertation) or Advisor (if thesis)

Shim, Moonsub

Doctoral Committee Chair(s)

Shim, Moonsub

Committee Member(s)

• Huang, Pinshane
• Kenis, Paul
• Shoemaker, Daniel

Department of Study

Materials Science & Engineerng

Discipline

Materials Science & Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• nanocrystal
• quantum dot
• semiconductor
• in situ
• spectroscopy
• QDLED
• QD-LED

Abstract

The recent Nobel prize in chemistry for the "discovery and synthesis of quantum dots" has brought considerable attention to the field of colloidal semiconductor nanocrystal synthesis. While quantum dots and their derivatives have considerable commercial potential, there have been consistent challenges in meeting that potential. From toxicity, to challenges in scaling, reproducibility, and reliability; transitioning from the laboratory to the real world is non-trivial. Addressing these challenges will be critical for the future deployment of quantum dot technologies. This work attempts to address specific facets of each of these challenges by developing approaches focused on data acquisition and analysis at a larger scale than has been previously reported. The toxicity problem can be partially addressed by exploring alternate chemistries. While the I-III-VI2 systems explored here do not yet exceed the performance of the existing II-VI systems, the growth of CuGaS2 nanorods and their heterostructures represents a rich opportunity to investigate the growth of nanoscale systems. Extensive investigation of the growth of the CuGaS2 nanorod system has revealed that previously proposed growth mechanisms fail to fully explain the behavior of this system. The concurrent seed growth and cation exchange (CSC) mechanism indicates that the growth of CuGaS2 nanorods (and similar systems) is a delicate balance between epitaxy and cationic exchange facilitated by superionic conduction. Additionally previously unexplained regioselective heteroepitaxy is explained via high-resolution transmission electron microscopy studies. "Solving" scaling and reproducibility in nanocrystal synthesis will certainly require more than can be described in this work, however this work aims to address these issues at least partially via the development of an in situ experimentation platform, coupled with increased computational integration. The design and fabrication of a high-temperature (>300°C) in situ optical probe capable of UV-Vis and Photoluminescence measurements is described, along with sample data demonstrating excellent time resolution. This probe was then used to examine the temperature-dependent properties of colloidal quantum dots at high temperature, in a regime that was previously inaccessible. Utilizing the temperature-dependence data obtained from the prior study, the rapid growth kinetics of quantum dots was examined as a function of temperature. These studies provide a foundation for reducing variability in quantum dot synthesis and the approach outlined herein provides a general means of evaluating the evolution of nanocrystal synthesis reactions with far greater detail than has been demonstrated previously. Finally, we have developed data-rich approaches to the non-destructive characterization of quantum-dot LEDs (QD-LEDs). While transient electroluminescence (TrEL) has been applied to QD-LEDs previously, the scale of our investigation, and the use of an offset voltage has provided considerable insight into charge transport in QD-LEDs. We anticipate that TrEL will continue to develop as a means of QD-LED characterization, and that further efficiency gains may be obtained by limiting the presence of mobile charges within QD-LEDs. Ultimately, the work presented here represents a move towards improved data gathering, utilization, and interpretation in all aspects of nanocrystals synthesis, and device fabrication.

Graduation Semester

2024-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2024 Logan Keating

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