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Halide perovskites have attracted considerable attention in next‐generation solid‐state lighting and displays owing to their outstanding optoelectronic properties. Over the past few years, perovskite light‐emitting diodes (LEDs) have achieved high external quantum efficiencies of >20% with active layers showing photoluminescence quantum efficiencies close to unity. This paper reviews the historical breakthroughs and recent advancements in perovskite LEDs with near‐infrared, red, green, and blue emission colors. Critical challenges, including device stability and material toxicity, are discussed. Finally, an outlook on white emission and lasing applications based on perovskite materials is presented.

Binary metal oxides offer improved anode materials in lithium ion batteries owing to enhanced electrical conductivity but suffer from large volume expansion on lithiation. A novel route to hollow Co3O4 nanospheres doped with ZnCo2O4 is demonstrated that mitigates the expansion issue and shows excellent performance at high current densities. The synthetic route is based on the pyrolysis of binary metal-organic-frameworks (MOFs) with the controlled loss of zinc tuning the micro and nanostructure of the material through a thermal vapor mechanism. The optimal structures, that contain hollow Co3O4 spheres of ca. 50 nm diameter doped with ZnCo2O4, show a specific capacity of 890 mAh g−1 at a current rate of 0.1 A g−1 and show a similar specific capacity at 1 A g−1 after 120 cycles at high current densities. The kinetics of lithiation/delithiation changes from diffusion-controlled to a surface-controlled process by the nanosizing of the particles. The resultant faster ion diffusion and capacitive storage for lithium ions are responsible for the extraordinary high-rate performance of the hollow structures.

International audience; Grain size in polycrystalline halide perovskite films is known to have an impact on the optoelectronic properties of the films, but its influence on their soft structural properties and phase transitions is unclear. Here, temperature-dependent X-ray diffraction, absorption, and macro- and micro-photoluminescence measurements are used to investigate the tetragonal to orthorhombic phase transition in thin methylammonium lead iodide films with grain sizes ranging from the micrometer scale down to the tens of nanometer scale. It is shown that the phase transition nominally at approximate to 150 K is increasingly suppressed with decreasing grain size and, in the smallest grains, the first evidence of a phase transition is only seen at temperatures as low as approximate to 80 K. With decreasing grain size, an increasing magnitude of the hysteresis is also seen in the structural and optoelectronic properties when cooling to, and then upon heating from, 100 K. This work reveals the remarkable sensitivity of the optoelectronic, physical, and phase properties to the local environment of the perovskite structure, which will have large ramifications for phase and defect engineering in operating devices.

Perovskite semiconductors are an exciting class of materials due to their promising performance outputs in photovoltaic devices. To boost their efficiency further, researchers introduce additives during sample synthesis, such as KI. However, it is not well understood how KI changes the material and, often, leaves precipitants. To fully resolve the role of KI, multiple microscopy techniques are applied and the electrical and chemical behavior of a Reference (untreated) and a KI‐treated perovskite are compared. Upon correlation between electrical and chemical nanoimaging techniques, it is discovered that these local properties are linked to the macroscopic voltage enhancement of the KI‐treated perovskite. The heterogeneity revealed in both the local electrical and chemical responses indicates that the additive partially migrates to the surface, yet surprisingly does not deteriorate the performance locally, rather, the voltage response homogeneously increases. The research presented within provides a diagnostic methodology, which connects the nanoscale electrical and chemical properties of materials, relevant to other perovskites, including multication and Pb‐free alternatives.

Quantum-confined CsPbBr3 nanoplatelets (NPLs) are extremely promising for use in low-cost blue light-emitting diodes, but their tendency to coalesce in both solution and film form, particularly under operating device conditions with injected charge-carriers, is hindering their adoption. We show that employing a short hexyl-phosphonate ligand (C6H15O3P) in a heat-up colloidal approach for pure, blue-emitting quantum-confined CsPbBr3 NPLs significantly suppresses these coalescence phenomena compared to particles capped with the typical oleyammonium ligands. The phosphonate-passivated NPL thin films exhibit photoluminescence quantum yields of ∼40% at 450 nm with exceptional ambient and thermal stability. The color purity is preserved even under continuous photoexcitation of carriers equivalent to LED current densities of ∼3.5 A/cm2. 13C, 133Cs, and 31P solid-state MAS NMR reveal the presence of phosphonate on the surface. Density functional theory calculations suggest that the enhanced stability is due to the stronger binding affinity of the phosphonate ligand compared to the ammonium ligand.