Multifunctional-Ligand Enabled Stable CsPbI3 Quantum Dots for Highly Efficient Pure-Red Light-Emitting Diodes

High-performance pure-red perovskite light-emitting diodes (PeLEDs) are promising candidates for optoelectronic applications due to their remarkable photophysical properties. However, the unstable surface and insulating long-chain capping ligands of perovskite quantum dots (QDs) pose challenges to their commercialization by compromising stability and performance. Here, a simple but effective approach was demonstrated to synthesize highly stable red CsPbI3 QDs by introducing a multifunctional molecule, phenformin hydrochloride (PhenHCl), as an additive ligand. While the biguanide functional group in PhenHCl formed multiple hydrogen-bond interactions with the lead halide octahedron, the excess Cl– anions compensated for the iodine vacancies and eliminated trap states in the CsPbI3 QDs. The synergistic effect of the biguanide functional group and halogen compensation significantly passivated surface defects of the red CsPbI3 QDs, yielding a photoluminescence (PL) quantum yield of 98.6% and excellent ambient stability with 90% PL intensity retention over 80 days. The resulting pure-red PeLEDs based on the PhenHCl-treated CsPbI3 QDs were demonstrated to show a remarkable enhancement in the electroluminescence performance at around 649 nm, with an external quantum efficiency of 13.38%, and a maximum luminance of 2159 cd m–2. Our findings in this work provide an avenue by modulating the surface chemistry of CsPbI3 QDs to enhance the performance of pure-red PeLEDs.