Controlling Parasitic Nucleation in Methylamine‐Treated Perovskite Films via Artificial Seeding and Phase‐Field Simulations

Large perovskite crystals with reduced defect density enable superior charge transport and stability. Therefore, controlling their nucleation and growth is key to advancing high‐performance optoelectronic devices based on perovskite semiconductors. Through the combination of a methylamine treatment and artificial nucleation sites, we demonstrate for the first time the preparation of hundreds‐of‐micrometer large perovskite crystals in a predefined spatial pattern. Nonetheless, certain configurations may lead to unwanted parasitic nucleation. To predict and mitigate this effect, we employ phase‐field simulations and develop an analytical model. Their predictive capability is demonstrated across three distinct material–substrate systems, enabling precise control over nucleation and subsequent crystal growth. Notably, the only material‐specific input required is the nucleation density (i.e., the number of crystals nucleated per unit area on an unpatterned substrate). This generality makes the models broadly applicable to diverse material systems for achieving controlled 2D crystallization for improved optoelectronic device performance.