Highly Efficient Pure-Blue Perovskite Light-Emitting Diode Leveraging CsPbBr_xCl_3−x/Cs₄PbBr_xCl_6−x Nanocomposite Emissive Layer with Shallow Valence Band

Metal-halide perovskite light-emitting diodes (PeLEDs) have shown great advancement in green, red, and near-infrared regions with external quantum efficiencies (EQEs) exceeding 20%. However, blue PeLEDs, an essential part of displays and lightings, show limited progress compared to the other color counterparts. Herein, a highly efficient pure-blue PeLED is demonstrated by leveraging a novel CsPbBr_xCl_3-x/Cs₄PbBr_xCl_6-x nanocomposite perovskite film as an emissive layer. The Cs₄PbBr_xCl_6-x phase, the derived phase of CsPbBr₃ perovskite with a mixed halide system, effectively passivates defects in CsPbBr_xCl_3-x, leading to high luminescence efficiency due to the significant reduction of nonradiative recombination. Furthermore, experimental and computational results confirmed that the compositionally optimized nanocomposite layer possesses a shallower valence band maximum (≈5.5 eV) than the pristine perovskite layer (≈5.9 eV), which is very advantageous in hole injection for device operation. The combined effects of the CsPbBr_xCl_3-x/Cs₄PbBr_xCl_6-x nanocomposite render the fabricated blue PeLED to exhibit a pure-blue emission at 470 nm with a maximum EQE of 5.3%.