Manipulating charge transfer dynamics and stabilizing lead bromide octahedra for efficient blue perovskite light-emitting diodes

Blue light-emitting diodes based on reduced-dimensional pure bromide perovskites have attracted increasing attention due to their superiority in achieving stable and efficient blue emissions. Yet, the employment of abundant insulating long-chain organic spacer cations severely limits the charge carriers transport capability and electroluminescence performance. Here, we utilize short-chain iminodi(methylphosphonic acid) ligand with two-terminated phosphonic groups that can strongly interact with the lead bromide octahedra via synergetic covalent bonds, facilitating the interlayer charge transfer and simultaneously reduces the defect density in perovskite films, thereby improving the light emission efficiency. Iminodi(methylphosphonic acid) ligand also enhances the dielectric confinement, leading to higher exciton binding energy and accelerated radiative recombination in perovskite emitters. The resulting blue light-emitting diode achieves a maximum external quantum efficiency of 25.4% and an operational lifetime exceeding 800 min, which represents a significant advancement among state-of-the-art blue light-emitting diodes based on pure bromide perovskites.