Folic Acid Passivated Efficient Cerium Doped Perovskite Nanocrystals for High‐Performance Light‐Emitting Diodes

The 5d → 4f transition of Ce 3+ is allowed by the electric dipole and the parity selection rule and the position/intensity of the 5d excited state is strongly dependent on the materials’ composition and atomic structure. Herein, the composition‐dependent luminescence properties of Ce 3+ in CsPbCl 3‐x Br x (0 ≤ x ≤ 3) perovskite nanocrystals (PeNCs) are systematically revealed. It's observed that the 5d ‐ 4f broadband emission of Ce 3+ is greatly improved by optimizing the Cl:Br ratio due to the efficient energy transfer from excitons to Ce 3+ . Folic acid, a vitamin which is an extremely important cofactor, is introduced to regulate the film formation by interacting with uncoordinated ions. The modified CsPbCl 1.5 Br 1.5 PeNCs with photoluminescence quantum yield of 91% represent a novel and extremely efficient white nanophosphor. Then, white light‐emitting diodes (WLEDs) are constructed by combining Ce 3+ ‐doped PeNCs with 400‐nm ultraviolet chips with a luminous efficiency of 120.3 lm W −1 , which is the most efficient perovskite single‐component WLED. Moreover, the blue‐violet LEDs are fabricated with external quantum efficiency of 0.84%, representing extremely high level of 400–435 nm perovskite LEDs. This work demonstrates the strategy in realizing high‐efficiency wavelength‐tunable PeNCs, motivating the further exploration of Ce 3+ ‐doped perovskites in optoelectronic devices.