Field-Driven Ion Migration and Color Instability in Red-Emitting Mixed Halide Perovskite Nanocrystal Light-Emitting Diodes

Perovskite nanocrystals have shown great promise as the basis of a new family of nanocrystal light-emitting diodes (LEDs). However, the external quantum efficiency and color stability of these materials still lag behind those of well-established technologies. Producing stable efficient red emitters with electroluminescence (EL) in the "pure" red range of 620–650 nm is a particular challenge. Here we present mixed halide CsPbBr3–xXx (X = I or Cl) peNC organic LEDs using peNC emitters with photoluminescence across the visible region to produce LEDs displaying EL across the visible spectrum. By focusing on the yellow-orange to deep red (560–680 nm) visible regime, we present evidence that field-driven halide separation in CsPbBr3–xIx peNCs is responsible for the observed red-shifting and splitting of the EL peaks. Greater compositional stability is demonstrated to be the key to higher efficiency, long-lived devices for deep red-emitting mixed halide peNCs with higher compositional concentrations of iodide.