# Multifunctional ligand engineering enables high-performance CsPb(Br/Cl)3 nanocrystals toward efficient and stable pure-blue perovskite LEDs

## TL;DR

Researchers developed a new method to improve the performance and stability of pure-blue perovskite LEDs using a special passivation molecule.

## Contribution

A novel passivation strategy using a multifunctional fluorinated phosphonic acid molecule enhances the performance and stability of pure-blue perovskite LEDs.

## Key findings

- HFPA passivation leads to a 14.8% external quantum efficiency in pure-blue PeLEDs.
- Device half-life is improved 13-fold compared to unmodified nanocrystals.
- Ion migration is effectively suppressed, enhancing device stability.

## Abstract

The development of pure-blue perovskite light-emitting diodes (PeLEDs) still lags behind that of green and red-emitting PeLEDs. Mixed halide (Br/Cl) perovskite nanocrystals (PeNCs) are commonly employed for blue emission but suffer from halide vacancies and ion migration. Here, we present a passivation strategy using the multifunctional fluorinated phosphonic acid molecule (1H,1H,2H,2H-heptadecafluorodec-1-yl)phosphonic acid (HFPA), which possesses active functional groups that improve the stability and electroluminescence performance of CsPb(Br/Cl)3 NCs. The HFPA molecule is shown to interact with uncoordinated Pb2+ on the PeNC surface through the phosphonate groups, concurrently establishing hydrogen bonds with adjacent halide ions. Moreover, the presence of fluorine atoms promotes ionic bond formation with the halide octahedra, thereby stabilizing the octahedral structure. The fabricated PeNC-LEDs exhibited a spectrally stable pure-blue emission peak at 467 nm, achieving a significantly improved external quantum efficiency (14.8%, 9-fold higher), maximum luminance (1052 cd·m-2, 10-fold higher), and half-life (342 s, 13-fold higher) compared to the device fabricated with unmodified CsPb(Br/Cl)3 NCs. Furthermore, the effective passivation of surface vacancies and stabilization of halogen ions by the HFPA molecules successfully suppressed ion migration in the PeNC-LEDs, thereby significantly enhancing the stability of the device.

Multifunctional fluorinated phosphonic acid passivates CsPb(Br/Cl)3 perovskite nanocrystals via phosphonate-Pb2+ coordination and hydrogen bond formation, achieving spectrally stable pure-blue LEDs with 14.8% EQE and 13-fold enhanced stability