(3bg) Interfacial Harnessing of Nanomaterial Heterostructures for Sustainable Energy Applications

Research Interests: The world's increasing energy demand has led to the novel advancement of nanomaterial-based energy devices, such as photovoltaics (PV), batteries, sensors, and smart windows. In order to further the development of nanomaterials in future energy devices, the field is now challenged with gaining a better understanding of nanomaterials in order to successfully engineer them. Given that a substantial number of atoms in nanomaterials reside on the surface and influence their optical and electronic properties, harnessing these surface interfaces is a need. The central aim of my research program is to further progress the development of nanostructures in order to produce energy devices by engineering the nanocrystal surface interfaces using solution process techniques. Increasing the viable material options and expanding the fabrication and deposition techniques for bottom-up device design can be explored further by leveraging the ease of synthesis, tunability of optical and electronic properties, and nanomaterials size. In this session, I present my previous endeavors on (i) the synthesis and interfacial engineering of surfactant coordinated nanoparticles for photovoltaic applications and (ii) understanding the effects on the electronic structures of thin film and 2D materials by varying interfacial chemistry. These projects serve as the foundation for the development of my research vision in the engineering of nanocrystal surface interfaces for energy related applications.

Research Experience: Solar power is a viable solution to the reduction of global dependence on non-renewable resources. The discovery that colloidal semiconducting nanomaterials can be synthesized via hot injection methods has led to the development of nano-inks to be used in the fabrication of nanocrystal-based PVs. The hot injection method is particularly novel due to the instant formation of homogenous nuclei upon the injection of the reactants into a hot solvent and surfactant (molecule/ligand) mixture. This method produces nearly monodispersed nanomaterials with a well-defined size and shape by coordinating the surfactants to the nanomaterial surface. This coordination not only influences the size and morphology of the nanomaterials, but it also has a strong effect on the properties of the nanomaterials as well. In order to create nanoparticles for PV devices, we investigated the nanocrystal-ligand interface effects on reaction yields, device performance, self-assembly, thermal stability, and optical properties for copper indium diselenide (CISe₂) and Cesium lead iodide (CsPbI₃) nanocrystals. We were able to show that the ligand selection influences the reaction yields and device performance for CISe₂ nanocrystal-based PVs. Although the self-assembly orientation structures were shown to be similar for disparately ligand-coordinated CsPbI₃ nanocrystals, a slight increase in the thermal stability, size, and optical properties were observed for surface ligand-coordination via phosphinic acid. This work illuminates the effects of the nanocrystal-ligand surface interfaces on nanocrystal properties and the development of stable colloidal nano-inks. Additionally, the engineering of these interfaces toward the desired properties was explored. These properties are important prerequisites to the fabrication of low-cost nanocrystal PV devices.

The future fabrication of sustainable energy devices relies on the successful stacking of multiple layers. This stacking creates heterostructure interfaces that affect the band alignment. As a result, we investigated the effects of substrate and grain/grain boundary heterostructure interfaces on electronic band structure and barrier heights of thin films and 2D materials. At the heterostructure interface, a few different types of band alignments can be formed that have a profound impact on the device properties. The band alignment includes the location of the valance band maximum and the conduction band minimum energy levels that governors the flow of excitons across the heterostructure interfaces. Therefore, understanding the shift in the energy bands at the heterostructure interfaces is paramount for the future development of energy devices. Through photoemission techniques, we illustrated the spatial band alignments of various heterostructure interfaces. We also found a dependence on carrier concentration with respect to the heterostructure interface. Photoemission techniques allow for the simultaneous extraction of microscopy and spectroscopy information for various materials resulting in nanoscale spatially resolved maps and spectra. Currently, we are investigating the Schottky barrier height and depletion width dependence at the grain/grain boundary heterostructure interfaces.

Teaching Interest: As I recall my time as a student, my most impactful teachers were those that were enthusiastic communicators and inspired student aspiration for lifelong learning and pursuit of personal ambition. It is because of these effective teachers, that I have focused my pedagogy on the principle that anything is possible when students are given the right tools to succeed. Specifically, I utilize both reconstructionism and constructivism teaching methodologies in my course curriculums. I accomplish this by incorporating social issues such as renewable energy, clean water, and engineering ethics into the fundamental chemical engineering course content. Given my teaching philosophy and experience, I am well-equipped to teach the core chemical engineering curriculum. My strongest topics include thermodynamics, unit operations, kinetics and reactor design, material and energy balances, and transport phenomena. In addition, I look forward to developing undergraduate and graduate courses on nanomaterials, surface characterization techniques, sustainable energy, and research practices.

A professor’s role is multifaceted and isn’t confined to the classroom or laboratory, but instead, extends into the community and individualize student interactions through outreach and mentorship opportunities. As a result, I frequently seek out opportunities to engage with my community in order to expand their knowledge on sustainable energy and fundamental engineering principles by performing and planning scientific demonstrations at outreach events. I also take pride in being a role model to future engineers, especially women and historically underrepresented groups. I have spoken and performed scientific demonstrations at events such as introduce a girl to engineering, explore UT, and local middle and high schools with aims to motivate and guide the younger generation into STEM careers. Ultimately, my aim as a faculty member is to 1) establish an inclusive classroom environment for students to learn and gain confidence in the subject matter, 2) to foster critical technical thinking skills through real-world applications, 3) to equip students with the resources to teach themselves, and 4) to nurture a foundation for effective technical communication. Through these tenets, I will provide my students with the tools necessary to become the engineers and scientists of tomorrow.

Selected Publications:

1. Yangning Zhang, Timothy D. Siegler, Cherrelle J. Thomas, Michael K. Abney, Tushti Shah, Anastacia De Gorostiza, Randalynn M. Greene, Brian A. Korgel. A “Tips and Tricks” Practical Guide to the Synthesis of Metal Halide Perovskite Nanocrystals. Mat., 2020, Accepted
2. Cherrelle J. Thomas, Yangning Zhang, Adrien Guillaussier, Khaled Bdeir, Omar F. Aly, Hyun Gyung Kim, Jungchul Noh, Lauren C. Reimnitz, Junjie Li, Francis Leonard Deepak, Detlef-M. Smilgies, Delia J. Milliron, Brian A. Korgel. Thermal Stability of the Black Perovskite Phase in Cesium Lead Iodide Nanocrystals Under Humid Conditions. Mat., 2019, 23, 9750-9758.
3. Yangning Zhang, Cherrelle J. Thomas, Adrien Guillaussier, Detlef-M. Smilgies, Brian A. Korgel. Thermal Phase Transitions in Superlattice Assemblies of Cuboidal CH₃NH₃PbI₃ Nanocrystals Followed by Grazing Incidence X-ray Scattering. J. Phys. Chem. C, 2019, 123, 17555-17565.
4. Taylor Harvey, Franco Bonafe, Ty Updegrave, Daniel Houck, Vikas Voggu, Cherrelle Thomas, Sirish Kamarajugadda, Carl Stolle, Douglas Pernik, Jiang Du, Brian Korgel. Uniform Selenization of Crack-Free Films of Cu(In,Ga)Se₂ACS Applied Energy Materials 2019, 2(1), 736-742.
5. Douglas R. Pernik, Marlene Gutierrez, Cherrelle Thomas, Vikas Reddy, Yixuan Yu, Joel van Embden, Alexander J. Topping, Jacek Jasieniak, David A. Vanden Bout, Raymond Lewandowski, Brian A. Korgel. Plastic Microgroove Solar Cells Using CuInSe₂ Nanocrystals, ACS Energy Letters, 2016 1 (5), 1021-1027.
6. Taylor Harvey, Franco Bonafé, Ty Updegrave, Cherrelle Thomas, Sirish Kamarajugadda, Jackson Stolle, Douglas Pernik, Jiang Du, Brian A. Korgel. 370984 Selenization of Automated, Ultra-Sonic Spray-Deposited Cu(In,Ga)Se₂ Nanocrystal Films for Photovoltaics. 14 AIChE Annual Meeting November 2014 (conference paper)