Navigating the vast, high-dimensional chemical space of colloidal nanocrystals remains a formidable challenge, as non-additive compositional and surface interactions render one-variable-at-a-time experimentation fundamentally insufficient for rational design with targeted optical properties. Autonomous, closed-loop synthesis platforms have emerged as powerful tools to address this, yet existing approaches are limited by optimizing crude reaction mixtures whose optical properties bear little resemblance to purified, processed material.

Here we present a closed-loop robotic platform based on our house-built Robowski ^[1,2], uniquely integrating automated synthesis, purification, post-synthetic passivation, and photophysical characterization within a single workflow, producing fully processed nanocrystals at a throughput exceeding 200 formulations per day. We apply this platform to the targeted discovery of highly photoluminescent deep blue-emitting mixed CsPbBr_3-xCl_x nanocrystals (λ_em < 465 nm), the most demanding color band for perovskite light-emitting diodes.

Robowski synthesizes monodisperse spheroidal CsPbBr₃ NCs via ligand-assisted nucleation at room temperature ^[3], followed by metal chloride exchange to blue-shift emission toward the target range. Twelve metal chlorides are systematically screened, seeding a closed-loop Bayesian optimization campaign, in which each cycle the platform synthesizes suggested compositions, acquires their photophysical data, and feeds the results back to the model to guide the next batch.

Navigating through a theoretical space of ~100,000 multi-metal co-dopant compositions, just 278 experiments across four iterative cycles successfully uncover a Zn-dominant domain as the most photoluminescent region. Subsequent exploration across ten post-synthetic passivation agents spanning inorganic cations, small organic ammoniums, and long-chain ammonium salts reveals that a synergistic combination of primary and quaternary long-chain ammonium salts achieves surface reconstruction inaccessible to either agent alone.

Manual validation of the champion formulation yields a near-unity photoluminescence quantum yield of 94.7% at λ_em = 458 nm even after three washing cycles, compared with 14.9% for untreated sample. Ranking among the highest reported PLQYs for deep blue-emitting perovskite nanocrystals, this work demonstrates the potential of accelerated, closed-loop robotic platforms as a powerful and enabling strategy for the targeted discovery of high-performance functional nanomaterials.