Exploiting Photohalide Generation in Shape and Multichromatic Color Patterning of Polymer-Perovskite Nanocomposites

The ability to arrange brightly fluorescent nanoscale materials into well-defined patterns is critically important in advanced optoelectronic structures. Traditional methods for doing so generally involve depositing different color quantum dot "inks," irradiating reactive (e.g., cross-linkable) ligands at their surface, and then lifting off the unexposed sections in a developer solvent. Here, we outline a fundamentally different approach for directly patterning the emission color of nanocomposite thin films utilizing mask-based lithographic techniques and laser scanning methods. In this system, a polymer film containing cesium lead halide nanocrystals (NCs) is embedded with an organohalide─termed a "photohalide generator"─which undergoes a light-triggered, perovskite-catalyzed reduction and release of halide anion for uptake by the NC lattice, markedly shifting its band gap. In this manner, a blue emitting (CsPbBr_1.5Cl_1.5) film becomes green and/or red in the exposed areas of a photomask, replicating the mask features as a multichromatic array (e.g., green, red, etc. colors against a blue background). The resolution limits of this materials system were probed using laser scanning tools capable of writing intricate patterns with feature sizes approaching a single micron─more than an order of magnitude smaller than the most comparable methods based on inkjet printing. Lastly, these methods are extended to a combined shape and color patterning process for making free-standing filamentous structures with striped and alternating fluorescence emission along their length.