Artificial Coater: An In Situ Self-Driving Lab Reveals Design Rules and Mechanisms for Ambient Perovskite Film Fabrication

Ambient solution-processing of metal halide perovskites remains highly sensitive to subtle variations in environment, formulation, and human technique, often leading to unpredictable outcomes and limited mechanistic understanding. Despite rapid advances in materials and device performance, researchers continue to rely heavily on manual and intuition-driven optimization, inconsistent fabrication protocols, and subjective film quality evaluation. These challenges persist across diverse coating methods, including but not limited to antisolvent dripping, which is especially sensitive to ambient manufacturing. In this work, we present the Artificial Coater, a self-driving laboratory platform that integrates closed-loop Bayesian optimization, in situ UV-Vis and photoluminescence spectroscopy, and machine vision to optimize thin film fabrication autonomously, reveal film formation mechanisms, and underlying root causes of unsuccessful fabrication. To enable scalable and unbiased interpretation of in situ spectral evolution, we apply non-negative matrix factorization across thousands of spectra, revealing latent spectral features associated with successful versus failed coatings. Using the benchmark composition FA₀.₈₃Cs₀.₁₇Pb(I₀.₈₃Br₀.₁₇)₃, we identify critical processing parameters governing crust formation, nucleation uniformity, and phase evolution. Our approach uncovers mechanistic insights into the formation of compact and uniformly converted perovskite thin films versus films exhibiting visibly rough morphologies across the coated area, links variations in morphology to solvent extractionmediated crystallization and reveals antisolvent drip design rules. This study establishes a dataintensive in situ framework with materials processing transparency, providing reusable and interpretable data for broader applications, including for potential transferability to other fabrication platforms and materials prepared using antisolvent drip.