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.