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

The 5d→4f transition of Ce³⁺ 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 Ce³⁺ in CsPbCl_3-xBr_x (0 ≤ x ≤ 3) perovskite nanocrystals (PeNCs) are systematically revealed. It's observed that the 5d-4f broadband emission of Ce³⁺ is greatly improved by optimizing the Cl:Br ratio due to the efficient energy transfer from excitons to Ce³⁺. 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_1.5Br_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 Ce³⁺-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 Ce³⁺-doped perovskites in optoelectronic devices.