Ligand-Pinning Induced Size Modulation of CsPbI₃ Perovskite Quantum Dots for Red Light-Emitting Diodes

Perovskite quantum dots (PQDs) show high potential for new-generation light-emitting diodes (LEDs) due to their outstanding optoelectronic properties. Even though the red PQD-LEDs can be realized through mixing halide in the PQDs to tune their spectroscopies, the PQDs may suffer from phase separation under a high electric field, predominantly affecting LED applications. Herein, a ligand-pinning-assisted approach is reported to tune the spectroscopies of CsPbI₃ PQDs, in which vinyl phosphonic acid (VPA) is applied as function ligands to regulate the nucleation and growth of PQDs during the synthesis. Systematically experimental studies and theoretical calculations are conducted to comprehensively understand the functions of the VPA ligands during the PQD synthesis, which reveals that the VPA ligands with high binding energy with Pb²⁺ cations could firmly anchor on the surface matrix of PQDs without desorption, regulating the growth of PQDs and thus resulting in tunable spectroscopies being realized. Meanwhile, VPA could also renovate the defective surface matrix of PQDs, substantially diminishing trap-induced nonradiative recombination. Consequently, red PQD-LEDs deliver a high external quantum efficiency of 22.83%, which is significantly improved compared with the control devices. This work provides a new avenue to tune the spectroscopies of PQDs toward high-performing LEDs.