Parinaz Moazzezi

Topic

Perovskite Single Crystals: Growth Kinetics, Solvent Interactions, and Photovoltaic Applications

Department of Electrical and Computer Engineering

Date & location

• Wednesday, August 19, 2026
• 9:00 A.M.
• Elliott Building, Room 228

Examining Committee

Supervisory Committee

• Dr. Makhsud Saidaminov, Department of Electrical and Computer Engineering, University of Victoria (Co-Supervisor)
• Dr. Reuven Gordon, Department of Electrical and Computer Engineering, UVic (Co-Supervisor)
• Dr. Arthur Blackburn, Department of Physics and Astronomy, UVic (Outside Member)

External Examiner

• Dr. Ghada Koleilat, Department of Electrical and Computer Engineering, Dalhousie University

Chair of Oral Examination

• Dr. Astrid Brousselle, School of Public Administration, UVic

Abstract

Metal halide perovskites have attracted considerable attention as semiconductor materials for photovoltaic applications owing to their strong light absorption, long charge-carrier diffusion lengths, and solution-processability. Among the various perovskite compositions, formamidinium lead iodide (FAPbI₃) is particularly attractive because of its near-optimal bandgap and favorable thermal stability. While single-crystal FAPbI₃ offers advantages over polycrystalline films, including reduced defect densities and the absence of grain boundaries, the growth of thin, phase pure crystals suitable for photovoltaic devices remains insufficiently understood. In particular, the relationships between crystallization kinetics, precursor chemistry, and crystal stability require further investigation to enable reproducible crystal growth and device fabrication. The objective of this thesis is to establish a fundamental understanding of these processes and to develop strategies for controlling the growth of FAPbI₃ single crystals under ambient conditions.

The first part of this work investigates the kinetics of space-confined inverse temperature crystallization, a widely adopted method for producing thin perovskite single crystals. Direct observation of the crystallization process revealed four sequential growth stages: saturation, nucleation, rapid growth, and slow growth. Analysis of these stages showed that crystal enlargement is primarily limited by restricted solute transport within the confined growth geometry and by competing nucleation events that deplete the available precursor solution. Based on these findings, crystallization approaches incorporating thickness and temperature gradients were developed to improve solute transport and regulate supersaturation during growth. These modifications increased crystal dimensions substantially and provided insight into the factors governing crystal growth under confined conditions.

The second part of the thesis focuses on the role of solvent chemistry during FAPbI₃ crystallization. A previously unrecognized cosolvency effect was identified in mixtures of γ-butyrolactone and 2 methoxyethanol, where FAPbI₃ exhibited greater solubility in the mixed solvent than in either solvent individually. Spectroscopic investigations revealed that interactions between the two solvents modify precursor solvation and delay crystallization to higher temperatures. This behavior suppresses the formation of the non-photoactive δ-phase and promotes the growth of phase-pure α- FAPbI₃ single crystals in ambient air. The improved control over crystallization enabled the fabrication of undoped FAPbI₃ single-crystal solar cells in ambient air and demonstrated an alternative route to phase stabilization that does not rely on compositional engineering.

The final part of this work examines the chemical evolution of precursor solutions during prolonged inverse temperature crystallization. While the mixed-solvent system enabled controlled crystal growth, extended heating was found to induce an unexpected redissolution of FAPbI₃ crystals. Combined spectroscopic and theoretical studies revealed that this behavior originates from an esterification reaction between γ-butyrolactone and 2-methoxyethanol that is facilitated by the perovskite precursor environment. The reaction alters the coordination chemistry of the solution and gradually destabilizes crystal growth. By adjusting precursor stoichiometry through slight PbI₂ deficiency, the extent of esterification was reduced, crystal redissolution was delayed, and the formation of phase-pure α- FAPbI₃ crystals was maintained for extended growth periods. These findings establish a direct connection between precursor stoichiometry, solvent reactivity, and crystal stability during inverse temperature crystallization.

Overall, this thesis demonstrates that the growth of FAPbI₃ single crystals is governed by a complex interplay between mass transport, solvent–solute interactions, and precursor chemistry. By investigating these factors across multiple length and time scales, this work provides new insight into the mechanisms that control perovskite crystallization and introduces practical strategies for producing larger, phase-pure FAPbI₃ single crystals under ambient conditions. The results contribute to the broader understanding of perovskite crystal growth and support the continued development of single-crystal perovskite photovoltaic technologies.