Sequential Ligand Exchange of All-Inorganic CsPbI₃ Perovskite Quantum Dots for Pure-Red Light-Emitting Diodes

Metal halide perovskite quantum dots (PQDs) are promising for next-generation optical displays, yet challenges persist in achieving pure-red emission (620–640 nm) due to a lack of effective ligand exchange methods for enhancing charge carrier transfer and stabilizing the PQDs structure/size during post-treatment. Herein, we report spectrally stable and efficient pure-red light-emitting diodes (LEDs) realized through sequential ligand post-treatment of all-inorganic CsPbI 3 PQDs. The as-synthesized CsPbI 3 PQDs (∼4 nm) undergo sequential purification steps, employing trioctylphosphine oxide (TOPO) and guanidinium iodide (GUAI) as ligands. This approach preserves the size and structure of the CsPbI 3 PQDs after two purification washes, improving the optoelectronic properties of CsPbI 3 PQD films and enables a stable electroluminescent emission centered at 640 nm with an external quantum efficiency (EQE) peaking near 15%. Our sequential ligand post-treatment successfully prevents the aggregation and coarsening of PQDs, presenting a novel approach toward enhancing the stability and efficiency of PQD-based LED technologies.