(585c) Controlling Morphology Via Nucleation and Evaporation in Solution-Processed Perovskite Thin Films

Solution-processed perovskite semiconductors are a promising material for the next generation of thin-film photovoltaics due to their facile deposition, easily tunable electronic properties, and the wide availability of existing printing and coating techniques. In practice however, the coupling of evaporation, nucleation, and crystal growth during film formation results in a complex process design space that unintuitively influences microstructure. The lack of definitive process-structure relationships has hindered the reliable design and implementation of scalable manufacturing techniques for large area perovskite photovoltaics (>1 cm²).^[1] To address these challenges, our past work includes a quasi-2D model to predict microstructure in evaporating and crystallizing thin films – which highlighted the importance of the confining vertical film height and horizontal diffusion length scales in determining the final film coverage and shape of crystalline domains.^[2]

In this study, we combine our past theoretical efforts with extensive confocal microscopy on perovskite films to understand the effects of process variables (temperature, concentration, solvent choice, evaporation rate) on the crystalline domain microstructure (surviving nuclei, topography). By measuring the nuclei spacing and domain height to characterize a film aspect ratio, we present a simple metric to quantify the relationship between nucleation/growth and evaporation dynamics. The film aspect ratios are found to depend largely on the solvent choice, while remaining relatively insensitive to temperature. For solvent blends (dimethylformamide/dimethyl sulfoxide), our models and experimental results reveal the dependence of final microstructure on the solvent environment at the time of supersaturation, which often differs significantly from the initial solvent composition and is difficult to predict without a comprehensive and quantitative understanding of the drying environment. This work provides insight into the interplay between evaporation, mass transport, and nucleation on the microstructure of crystallizing thin films. These findings provide a path forward for developing quantitative and scalable manufacturing strategies for solution-processed photovoltaics.

[1] Champion Photovoltaic Module Efficiency Chart (n.d.), https://www.nrel.gov/pv/module-efficiency.html. (Accessed 8 April 2024).

[2] Jesse L. Starger, Aaron T. Fafarman, Jason B. Baxter, Nicolas J. Alvarez, and Richard A. Cairncross, Langmuir 2023 39 (46), 16231-16243, 10.1021/acs.langmuir.3c01469