Achieving high-performance perovskite light-emitting diodes (PeLEDs) with pure-red electroluminescence for practical applications remains a critical challenge because of the problematic luminescence property and spectral instability of existing emitters. Herein, high-efficiency Rec. 2020 pure-red PeLEDs, simultaneously exhibiting exceptional brightness and spectral stability, based on CsPb(Br/I)(3) perovskite nanocrystals (NCs) capping with aromatic amino acid ligands featuring cation-pi interactions, are reported. It is proven that strong cation-pi interactions between the PbI6-octahedra of perovskite units and the electron-rich indole ring of tryptophan (TRP) molecules not only chemically polish the imperfect surface sites, but also markedly increase the binding affinity of the ligand molecules, leading to high photoluminescence quantum yields and greatly enhanced spectral stability of the CsPb(Br/I)(3) NCs. Moreover, the incorporation of small-size aromatic TRP ligands ensures superior charge-transport properties of the assembled emissive layers. The resultant devices emitting at around 635 nm demonstrate a champion external quantum efficiency of 22.8%, a max luminance of 12 910 cd m(-2), and outstanding spectral stability, representing one of the best-performing Rec. 2020 pure-red PeLEDs achieved so far.

Pure-red perovskite LEDs (PeLEDs) based on CsPb(Br/I)(3) nanocrystals (NCs) usually suffer from a compromise in emission efficiency and spectral stability on account of the surface halide vacancies-induced nonradiative recombination loss, halide phase segregation, and self-doping effect. Herein, a "halide-equivalent" anion of benzenesulfonate (BS-) is introduced into CsPb(Br/I)(3) NCs as multifunctional additive to simultaneously address the above challenging issues. Joint experiment-theory characterizations reveal that the BS- can not only passivate the uncoordinated Pb2+-related defects at the surface of NCs, but also increase the formation energy of halide vacancies. Moreover, because of the strong electron-withdrawing property of sulfonate group, electrons are expected to transfer from the CsPb(Br/I)(3) NC to BS- for reducing the self-doping effect and altering the n-type behavior of CsPb(Br/I)(3) NCs to near ambipolarity. Eventually, synergistic boost in device performance is achieved for pure-red PeLEDs with CIE coordinates of (0.70, 0.30) and a champion external quantum efficiency of 23.5%, which is one of the best value among the ever-reported red PeLEDs approaching to the Rec. 2020 red primary color. Moreover, the BS--modified PeLED exhibits negligible wavelength shift under different operating voltages. This strategy paves an efficient way for improving the efficiency and stability of pure-red PeLEDs.

The development of perovskite light-emitting diodes (PeLEDs) with both high efficiency and excellent stability remains challenging. Herein, a strong correlation between the lattice strain in perovskite films and the stability of resulting PeLEDs is revealed. Based on high-efficiency PeLEDs, the device lifetime is optimized by rationally tailoring the lattice strain in perovskite films. A PeLED with a high peak external quantum efficiency of 18.2% and a long lifetime of 151 h (T-70, under a current density of 20 mA cm(-2)) is realized with a minimized lattice strain in the perovskite film. In addition, an increase in the lattice strain is found during the long-time device stability test, indicating that the degradation of the local perovskite lattice structure could be one of the degradation mechanisms for long-term stable PeLEDs.

The development of highly efficient blue perovskite light-emitting diodes (PeLEDs) remains a big challenge, requiring more fundamental investigations. In this work, significant photoluminescence enhancement in mixed halide blue perovskite films is demonstrated by using a molecule, benzylphosphonic acid, which eventually doubles the external quantum efficiency to 6.3% in sky-blue PeLEDs. The photoluminescence enhancement is achieved by forming an oxide-bonded perovskite surface at grain boundaries and suppressing electron-phonon interaction, which enhances the radiative recombination rate and reduces the nonradiative recombination rate, respectively. Moreover, severe thermal quenching is observed in the blue perovskite films, which can be explained by a two-step mechanism involving exciton dissociation and electron-phonon interaction. The results suggest that enhancing the radiative recombination rate and reducing the electron-phonon interaction-induced nonradiative recombination rate are crucial for achieving blue perovskite films with strong emission at or above room temperature.

Metal halide perovskites have demonstrated impressive properties for achieving efficient monochromatic light-emitting diodes. However, the development of white perovskite light-emitting diodes (PeLEDs) remains a big challenge. Here, we demonstrate a single-emissive-layer all-perovskite white PeLED using a mixed halide perovskite film as the emissive layer. The perovskite film consists of separated mixed halide perovskite phases with blue and red emissions, which are beneficial for suppressing halide anion exchange and preventing charge transfer. As a result, the white PeLED shows balanced white light emission with Commission Internationale de L'Eclairage coordinates of (0.33, 0.33). In addition, we find that the achievement of white light emission from mixed halide perovskites strongly depends on effective modulation of the halide salt precursors, especially lead bromide and benzamidine hydrochloride in our case. Our work provides very useful guidelines for realizing single-emissive-layer all-perovskite white PeLEDs based on mixed halide perovskites, which will spur the development of high-performance white PeLEDs.