Dual Confinement Modulation in Perovskite Nanocrystals Enabled Near‐Standard‐Green Emission With Invariant Chromaticity

Quantum and dielectric confinement critically govern the intrinsic emission wavelength of perovskite nanocrystals, however achieving precise and simultaneous control over both remains challenging. Here, we report a surface‐driven reconstruction strategy for in situ‐formed nanocrystals on the substrate, enabling dual confinement modulation. In this process, the originally attached bulky organic ammonium ligands reorganize to promote crystal growth, whereas the subsequently introduced covalently bound phosphonic acid ligands control particle size and co‐assemble into a compact dielectric shell. Spectroscopic ellipsometry reveals an increased dielectric permittivity of the ligand shell, indicating enhanced dielectric screening that modulates Coulomb interactions and induces band‐edge renormalization, enabling finely tunable redshifts into the near‐standard green emission regime. The emission followed an empirical bandgap relation governed by nanocrystal size and the local dielectric environment, revealing that surface‐driven reconstruction of substrate‐grown in situ nanocrystals provides deterministic control over both quantum and dielectric confinement. Devices exhibited near‐standard‐green emission at (0.177, 0.769) with exceptionally small chromaticity deviation of Δ u′v′ ≤0.0014 across the operating voltage range and ≤0.0027 from over a viewing range of 0°–80°, far outperforming the tolerances required for advanced display (≤0.02), medical imaging systems (≤0.01) and AR/VR devices of 0.007.