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 CsPbI3 PQDs. The as-synthesized CsPbI3 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 CsPbI3 PQDs after two purification washes, improving the optoelectronic properties of CsPbI3 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.