Switchable Anion Exchange in Polymer-Encapsulated APbX3 Nanocrystals Delivers Stable All-Perovskite White Emitters

We report a one-step synthesis of halide perovskite nanocrystals embedded in amphiphilic polymer (polyacrylic acid-block-polystyrene, PAA-b-PS) micelles, based on injecting a dimethylformamide solution of PAA-b-PS, PbBr₂, ABr (A=Cs, formamidinium, or both) and “additive” molecules in toluene. These bi-functional or tri-functional short chain organic molecules improve the nanocrystals-polymer compatibility, increasing the nanocrystal stability against polar solvents and high flux irradiation. If the nanocrystals are suspended in toluene, the coil state of the polymer allows the nanocrystals to undergo halide exchange, enabling emission color tunability. If the NCs are suspended in methanol, or dried as powders, the polymer is in the globule state, and they are inert to halide exchange. The nanocrystals retain almost 80% of their photoluminescence after one hour of 3.2 w/cm² irradiation. By mixing three primary colors we could prepare stable, multicolor emissive samples (for example white emitting powders) and a UV-to-white color converting layer for light-emitting diodes made of fully perovskite nanocrystals.