Diana LaFollette
Advisor: Prof. Juan-Pablo Correa-Baena

will defend a doctoral thesis entitled,

Chemistry-Structure-Property Relationships in Lead Halide Perovskites for Optoelectronic Applications

On

Tuesday, April 14 at 2:00 pm
MRDC 4211

and/or

 Virtually via MS Teams

https://teams.microsoft.com/meet/21959721628546?p=jM3cLqhbDq77zjnFq4

Meeting ID: 219 597 216 285 46

Passcode: Sj93Nr9o

Committee
            Prof. Juan-Pablo Correa-Baena – School of Materials Science and Engineering (advisor)
            Prof. Seung Soon Jang – School of Materials Science and Engineering
            Prof. Matthew McDowell – School of Materials Science and Engineering

      Prof. Natalie Stingelin - School of Materials Science and Engineering

      Prof. Michael Toney - School of Chemical and Biological Engineering, University of Colorado Boulder

Abstract

Lead halide perovskite (LHP) solar cells have made impressive advancements in solar energy conversion, surpassing 27% power conversion efficiencies in only 15 years of development. Despite these competitive efficiencies, the road to commercialization of perovskite solar cells is limited by poor long-term stability that can be tied to the LHP crystal structure. Varying strategies, including compositional engineering and interfacial modifications, have been explored to improve stability, but further progress relies on understanding the fundamental mechanisms driving degradation. This dissertation addresses this challenge by investigating chemistry-structure-property-performance relationships in lead halide perovskites using advanced characterization techniques.

The first chapter explores the role of composition on LHP stability as a function of annealing temperature. While most high-performing solar cells use mixed-cation, mixed-halide compositions, fundamental studies on phase transformations often fail to account for this complexity. This work demonstrates that small compositional changes significantly affect phase transformations as a function of annealing temperature, showing that mixed-cation, mixed-halide phase transformations cannot be approximated by linear interpolation between pure species. Building on this understanding, the second part of this dissertation engineers the crystallization of complex compositions using lattice matching. This chapter expands the role of lattice matching beyond structural templating, demonstrating its ability to homogenize phase segregation, reduce ion migration, and improve optoelectronic film quality, setting the stage for future device integration. Finally, the third part of this dissertation systematically investigates how ligand-ligand interactions affect crystallization, phase segregation, and dimensionality in lower dimensional perovskites. This work provides key fundamental knowledge on lower-dimensional perovskite crystallization, enabling future studies of phase-segregated systems, the formation of 2D/3D heterostructures, and the relationship between structure and environmental stability.

Using advanced characterization, this dissertation proposes mechanisms that link chemistry, structure, and properties across length scales, considering defect formation, strain, phase segregation, ion migration, and phase transformations. In doing so, this dissertation lays the groundwork for improving the stability of perovskite solar cells and provides broadly applicable insights for developing other LHP-based optoelectronic devices.