Researchers from Shaanxi University of Science & Technology, Henan Academy of Sciences and North China Electric Power University have developed a dual-active-site ligand strategy to address one of the most persistent challenges in mixed-halide perovskite nanocrystal LEDs: halide ion migration and the resulting spectral instability.
Mixed Br/I CsPbI₃₋ₓBrₓ nanocrystals are widely considered the most viable route to achieving pure-red emission in the 620-650 nm range required by the Rec. 2020 display standard (CIE coordinates ~0.708, 0.292). However, under an applied electric field, mobile halide ions (Br⁻ and I⁻) readily migrate through vacancy-mediated hopping pathways. This leads to phase segregation into bromide-rich and iodide-rich domains, causing irreversible spectral shifts, efficiency loss, and device degradation. While external quantum efficiencies (EQEs) of pure-red perovskite LEDs have exceeded 20% in recent years, operational spectral stability remains a key bottleneck.
To tackle this, the team introduced tris(1-chloro-2-propyl) phosphate (TCPP) via an in-situ ligand coordination approach. TCPP features two complementary active sites: phosphoryl (P=O) groups and chloride ions. These enable synergistic binding at the nanocrystal surface, forming strong interfacial interactions with the perovskite lattice. Mechanistically, this dual-site coordination plays two critical roles. First, it passivates surface defects and suppresses nonradiative recombination, improving radiative efficiency. Second - and more importantly - it creates a dense ion-blocking layer that inhibits halide vacancy formation and ion migration at both surface and interface regions, effectively suppressing phase segregation under electrical bias.
As a result, the fabricated CsPb(Br/I)₃ PeLEDs exhibit stable pure-red electroluminescence centered at 650 nm, closely matching Rec. 2020 color specifications. The devices achieve a maximum EQE of 24.62%, along with a peak luminance of 3319 cd m⁻² and an operational lifetime (T₅₀) of 248 minutes. Notably, the emission maintains CIE coordinates of (0.708, 0.292) during operation, confirming excellent spectral stability.
This work highlights the importance of simultaneously addressing defect passivation and ion migration. By integrating both functions into a single ligand system, the study provides a practical pathway toward high-efficiency, color-stable pure-red perovskite LEDs suitable for next-generation display technologies.
