Foundational Studies of the Deposition of Metal-Halide Perovskite Thin Films by Resonant Infrared, Matrix-Assisted Pulsed Laser Evaporation

Metal-halide perovskites (MHP) comprise a diverse family of crystalline materials whose optoelectronic properties have gathered significant interest recently. Their use in transistors, solar cells, light emitting diodes, and many other applications with significant real-world impacts has been enabled by synthesis techniques that can deposit high quality MHP thin films. The simple yet powerful chemistry involved in solution-processing techniques has allowed for MHP thin films to be deposited in a variety of different ways like spin-coating, inkjet printing, and doctor blading. However, solvent in these techniques can preclude the creation of advanced MHP structures like graded composition films or all-MHP heterojunctions. Additionally, the poor solubility of complex organic moieties in the polar solvents used in solution-processing of MHP materials could prevent the creation of MHP materials with unique photophysical properties. The development of vapor-processing techniques which circumvent the use of solvent to vaporize MHP precursors and deposit thin films has shown promise in addressing these concerns with solution-processing. However, the use of highly energetic precursor vaporization mechanisms has itself raised worries about its broad applicability.

In this dissertation, the deposition of MHP thin films using Resonant Infrared, Matrix-Assisted Pulsed Laser Evaporation (RIR-MAPLE) is developed as an alternative to current MHP thin film deposition techniques. The ‘dry’ deposition of materials under dynamic vacuum and the use of a low energy infrared laser directly address shortcomings of solution- and vapor-processing techniques, respectively. Using the understanding of RIR-MAPLE developed by previous studies, a double solvent approach was first developed to solubilize and deposit MHP precursors in a manner which maintained the integrity of the resulting films. The viability of this baseline approach was confirmed through the creation of MHP solar cells with competitive performance and thin films of MHP materials with complex organic moieties that demonstrate unique photophysical properties. Subsequent studies of nuanced aspects in RIR-MAPLE deposition of MHP thin films helped develop an understanding of the process-structure-property relationships in play during RIR-MAPLE deposition and in post-processing of the resulting MHP thin films.

Following these baseline studies, unique precursor delivery schemes were developed to demonstrate the versatility of RIR-MAPLE. These schemes were shown to reliably deposit continuous films of MHP materials despite differences in the state of precursors during deposition and crystallization. Finally, a comprehensive study of MHP film formation mechanisms during RIR-MAPLE deposition was undertaken. These experiments categorically described the wetting, nucleation, diffusion, and accumulation essential to MHP film development during RIR-MAPLE deposition. Overall, this work demonstrates some of the most promising aspects of the RIR-MAPLE deposition technique and develops the candidacy of RIR-MAPLE as an MHP thin film technique uniquely positioned to address the shortcomings of other currently established methods.