Stabilization of γ-CsPbI₃ Nanoplatelets via Tailored Surface Coordination for High-Performance Rec. 2020 Pure-Red...

Pure-red perovskite light-emitting diodes (PeLEDs) are critical for next-generation displays, while existing systems based on mixed Br/I compositions, quasi-2D phases, or colloidal 0D quantum dots are still facing challenges in fulfilling the requirements of the Recommendation BT.2020 (Rec. 2020) red standard. CsPbI₃ nanoplatelets (NPLs) whose bandgap depends on thickness-size are a promising candidate for pure-red light-emitting emitters, but their practical use as LEDs has been hampered by the metastability of the emissive CsPbI₃ cubic phase. Here, we report the synthesis of stabilized γ-CsPbI₃ NPLs with a tailored surface coordination by incorporating a trace amount of dimethyl sulfoxide (DMSO) and N,N'-dimethylpropyleneurea (DMPU) into the precursor. These ligands selectively coordinate with undercoordinated Pb²⁺ sites in [PbI₆]^4- octahedra through Lewis acid-base interactions, redistributing the electron density at Pb centers and inducing lattice distortion by the Pb-I-Pb bond angle torsion, thereby stabilizing the γ-phase. The complementary effect of the polarities and the coordination capacities of DMSO/DMPU guide anisotropic growth along the [100] direction, enabling atomic-precision control of the NPL thickness (4 monolayers) to tailor the quantum-confined pure-red emission. The resultant pure-red PeLEDs achieve Commission Internationale de l'Eclairage (CIE) coordinates of (0.708, 0.292), 100% compliance with the Rec. 2020 specification, as well as an external quantum efficiency (EQE) of over 12% and a superior operational lifetime with a half-lifetime (T₅₀) of 360 min, representing the highest reported values for CsPbI₃ NPL-based PeLEDs.