Functional Polymer Ligands Modulate Phase Transitions and Photoluminescence of Cesium Copper Iodide Nanocrystals

Cesium copper(I) halide nanocrystals (NCs), such as those with Cs₃Cu₂I₅ stoichiometry, are high quantum yield broadband emitters that are enticing prospects for applications as lead-free perovskite NCs, such as in light-emitting displays and X-ray scintillation constructs. Combined with their favorable sustainability owing to the absence of lead, the photoluminescence emission of these NCs uniquely transitions from blue (the Cs₃Cu₂I₅ phase) to yellow (the CsCu₂I₃ phase) upon exposure to water or alcohols, yielding NCs composed of mixed phases that emit white light. Here, we describe nanocomposites of Cs₃Cu₂I₅ NCs with ligand-bearing polymers that provide distinct control over the phase transitions. The selection of functional groups in the polymer ligands─e.g., carboxylates, tertiary amines, and N-oxides─uniquely altered NC phase transitions, ranging from preventing such transitions to facilitating them and, in some cases, enabling reversibility between phases. These findings led to the implementation of ligand-functionalized polymers in combination with silicone stamps to produce patterned films of different shapes and emission wavelengths.