Efficient and spectrally stable pure-red perovskite light-emitting diodes (PeLEDs) are still rare and urgently needed for high-definition display. The traditional color tuning method by varying halide composition undergoes phase segregation and has spectral instability issues. Instead of halide mixing, we fabricate pure-red PeLEDs based on quasi-two-dimensional (quasi-2D) perovskites by simultaneously incorporating phenethylammonium (PEA) and 1-naphthylmethylammonium (NMA) cations. The control of PEA and NMA cospacer ratio modulates the phase distribution and the resulting different color emission. The PeLEDs with PEA:NMA molar ratio of 5:5 exhibit a pure-red (635 nm) electroluminescence (EL) with a CIE coordinate (0.709, 0.285) approaching the Rec. 2020 specification. Meanwhile, the optimized devices exhibit an external quantum efficiency (EQE) of 12.41% and a maximum brightness of 1452.6 cd m–2, which are among the best-performing pure-red PeLEDs based on quasi-2D perovskite to date. Additionally, our PeLEDs demonstrate stable EL spectra under different operating voltages and continuous operation.

Quasi-2D perovskite light-emitting diodes (PeLEDs) have attracted significant attention for their promising light-emitting applications. However, quasi-2D perovskite films typically consist of a broad phase distribution and small grains with a large surface area to volume ratio, leading to inferior color purities and higher defect densities. Herein, a bifunctional additive ((l)-tryptophan bromide, l-TrpBr) was introduced into a quasi-2D perovskite film. The CO moiety of l-TprBr formed hydrogen bonds with S-MBA+, retarding the coordination between S-MBABr and [PbBr6]4– and suppressing the formation of small-n phases. The CO moiety also coordinated with unsaturated Pb2+ sites to passivate the defects. Finally, the PeLEDs with l-TrpBr exhibited a significantly improved EQE of 14.32% compared to the control devices (7.88%) and the narrowest fwhm (17 nm) for green quasi-2D PeLEDs reported to date. Our work provides a practical approach to controlling the phase distribution and passivating the defects in quasi-2D perovskite films, toward high-efficiency and color-pure quasi-2D PeLEDs.

Adjustable zero-phase delay and equiphase control are demonstrated in single and multilayer dielectric particle arrays with high index and low loss. The polarization-independent near-zero permeability is the origin of the wave control near the first Mie magnetic resonance. The proposed design paves the way for subwavelength devices and opens up new avenues for the miniaturization and integration of THz and optical components.