Pure-red electroluminescence of quantum-confined CsPbI3 perovskite nanocrystals obtained by the gradient purification method

Pure-red emission light-emitting diodes (LEDs) are highly desirable for display and lighting applications. Here, we present a synergistic approach to fabricate pure-red emission LEDs based on quantum-confined CsPbI3 nanocrystals (NCs). By introducing ZnI2 acting as a co-precursor and passivating agent into the synthesis, and applying a gradient post-synthesis purification method allowing us to obtain size-selected fractions with precisely adjusted emission colors, we obtained uniform and small (about 6 nm), quantum-confined CsPbI3 NCs exhibiting high stability in ambient conditions and a superior photoluminescence quantum yield of up to 88%. These NCs exhibited the tendency to undergo oriented attachment, resulting in self-assembled superstructures with a pure-red emission at 629 nm. Importantly, partial recrystallization into fused superstructures led to removal of the insulating ligand barriers between NCs. LEDs based on the CsPbI3 NCs showed pure-red electroluminescence at 633 nm, with an external quantum efficiency of 14.7% and a luminance of over 1000 cd/m2. Our study reveals the mechanism behind the oriented attachment and assembly of small, quantum-confined CsPbI3 NCs, and contributes to the development of pure-red electroluminescent LEDs.