A recent University at Buffalo (SUNY) study has shown that a fluorinated multifunctional ligand can dramatically improve both efficiency and stability in deep-blue CsPb(Br/Cl)₃ perovskite nanocrystal LEDs by suppressing defect formation and halide ion migration.
Deep-blue PeLEDs require emission in the 460-470 nm range, which can be realized either with mixed-halide CsPb(Br/Cl)₃ nanocrystals or with strongly quantum-confined CsPbBr₃ nanoplatelets. Quantum-confined CsPbBr₃ NPLs have demonstrated 461 nm emission with a 13 nm FWHM and 96% PLQY, enabling REC.2020-compliant deep blue (CIE (0.135, 0.046)), but EQE remains below 7%. Mixed-halide CsPb(Br/Cl)₃ offers a more direct compositional route, yet is prone to halide vacancies and instability, as seen in formamidinium-doped CsPb(Cl₀.₅Br₀.₅)₃ PeNCs that reach 1452 cd m⁻² but only 5% EQE and a peak at 474 nm, slightly red of the target window. In the new work, HFPA-engineered CsPb(Br/Cl)₃ emitters are tuned specifically for operation in the 460-470 nm pure-blue range, directly targeting display-relevant color coordinates.
The central advance is replacing conventional oleic acid/oleylamine ligands with (1H,1H,2H,2H-heptadecafluorodec-1-yl)phosphonic acid (HFPA), a short, strongly binding fluorinated phosphonic acid that passivates the CsPb(Br/Cl)₃ nanocrystal surface through multiple interactions. Standard OA/OAm are relatively labile and electrically insulating, leaving the surface vulnerable to dynamic ligand loss, defect formation and inefficient charge transfer under bias. In contrast, HFPA’s phosphonate groups coordinate under-coordinated Pb²⁺ sites, hydrogen bonding stabilizes nearby halide ions, and the fluorinated segment further stabilizes the halide octahedra, as supported by DFT analysis. The ligand’s short length preserves efficient charge transfer between the nanocrystals and transport layers while stabilizing surface halides and suppressing ion migration and Cl⁻ vacancy formation.
In otherwise identical device architectures, HFPA treatment increases EQE, maximum luminance and operational half-life by factors of 9, 10 and 13, respectively, compared to OA/OAm-capped references. It also effectively “locks” the emission wavelength: unmodified devices show the typical red-shift at higher drive voltages, whereas HFPA-modified devices maintain a stable spectrum, indicating strongly reduced halide migration.
Taken together, these metrics place the HFPA-based devices beyond the previously reported EQE–luminance Pareto front for deep-blue PeLEDs, indicating a genuine performance step. Although the absolute lifetime remains short (half-life below six minutes in a glove box) and still far from commercial requirements, the work positions multifunctional fluorinated phosphonic acids as a powerful handle to simultaneously optimize surface passivation, halide stability and charge transfer in mixed-halide deep-blue emitters.
