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Light-emitting diodes (LEDs) with different emission spectra are widely used in daily life for a variety of applications. However, due to fundamental restrictions of light-emitting materials, the development of near-infrared LEDs (NIR-LEDs) is still modest. Recently, solution-processed tin-halide perovskites (THPs) have emerged as one of the most promising light-emitting materials for NIR-LED applications. In this Perspective, we start with discussing the peculiarities of THP semiconductors and how their electronic properties affect the light emission efficiency. We then summarize the current efforts in material engineering to design and master the electronic properties of THP films. Finally we give an outlook on the future challenges and technical roadmap for tin-based perovskite LEDs., Funding Agencies|H2020 European Research Council [771528, 101105123]; ERC; Distinguished Scientist Fellowship Program (DSFP) of King Saud University, Riyadh, Saudi Arabia

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., Funding Agencies|Swedish Energy Agency Energimyndigheten [48758-1]; China Postdoctoral Science Foundation [2020M673055]; NSFC [61774077]; Research and Development Program in Key Areas of Guangdong Province [2019B1515120073, 2019B090921002, 2019B010132004]; [895679]

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., Funding Agencies|ERC Starting Grant [717026]; Swedish Foundation for International Cooperation in Research and Higher Education [CH2018-7736]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; European Union [823717 - ESTEEM3]; [895679]

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., Funding Agencies|This work was supported by the National Key Ramp;D Program of China (2022YFB3603003), the Swedish Research Council Vetenskapsrdet (grant 2020-03564), and the Swedish Government Strategic Research Area in Materials Science on Functional Materials at [2022YFB3603003]; National Key Ramp;D Program of China [2020-03564]; Swedish Research Council Vetenskapsrdet [2009-00971]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkping University [214-0364]; Olle Engkvists Byggmstare Stiftelse [61774077]; National Natural Science Foundation of China Project [2019B1515120073, 2019B090921002, G20200019046]; Key Projects of Joint Fund of Basic and Applied Basic Research Fund of Guangdong Province [KFVE20200006]; Guangzhou Key Laboratory of Vacuum Coating Technologies and New Energy Materials Open Projects Fund [12074347, 61935009]; National Natural Science Foundation of China [212300410019]; Science Foundation for Distinguished Young Scholars of Henan Province [2020A1515110527, 2020A1515110384]; Guangdong Basic and Applied Basic Research Foundation

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., Funding Agencies|Guangdong Basic and Applied Basic Research Foundation [2020A1515110527, 2020A1515110384]; National Natural Science Foundation of China [61774077, 62104083, 51625301, 91733302, 51861145301, 12074347, 61935009]; Key Projects of Joint Fund of Basic and Applied Basic Research Fund of Guangdong Province [2019B1515120073, 2019B090921002]; Research Fund of Guangdong-Hong Kong-Macao Joint Laboratory for Intelligent Micro-Nano Optoelectronic Technology [2020B1212030010]; Science Foundation for Distinguished Young Scholars of Henan Province [212300410019]