Explore the vast range of titles available.

Lead halide perovskites (LHPs) in the form of nanometre-sized colloidal crystals, or nanocrystals (NCs), have attracted the attention of diverse materials scientists due to their unique optical versatility, high photoluminescence quantum yields and facile synthesis. LHP NCs have a ‘soft’ and predominantly ionic lattice, and their optical and electronic properties are highly tolerant to structural defects and surface states. Therefore, they cannot be approached with the same experimental mindset and theoretical framework as conventional semiconductor NCs. In this Review, we discuss LHP NCs historical and current research pursuits, challenges in applications, and the related present and future mitigation strategies explored.

The strong interaction of individual quantum emitters with resonant cavities is of fundamental interest for understanding light–matter interactions. Plasmonic cavities hold the promise of attaining the strong coupling regime even under ambient conditions and within subdiffraction volumes. Recent experiments revealed strong coupling between individual plasmonic structures and multiple organic molecules; however, strong coupling at the limit of a single quantum emitter has not been reported so far. Here we demonstrate vacuum Rabi splitting, a manifestation of strong coupling, using silver bowtie plasmonic cavities loaded with semiconductor quantum dots (QDs). A transparency dip is observed in the scattering spectra of individual bowties with one to a few QDs, which are directly counted in their gaps. A coupling rate as high as 120 meV is registered even with a single QD, placing the bowtie-QD constructs close to the strong coupling regime. These observations are verified by polarization-dependent experiments and validated by electromagnetic calculations. Strong coupling at the limit of a single quantum emitter has not been reported. Here, Santhosh et al. show a transparency dip is observed in the scattering spectra of individual silver bowties with one to a few quantum dots, placing the plasmonic bowtie-quantum dot constructs close to the strong coupling regime.

Artificial photosynthesis of H 2 O 2 from H 2 O and O 2 , as a spotless method, has aroused widespread interest. Up to date, most photocatalysts still suffer from serious salt-deactivated effects with huge consumption of photogenerated charges, which severely limit their wide application. Herein, by using a phenolic condensation approach, carbon dots, organic dye molecule procyanidins and 4-methoxybenzaldehyde are composed into a metal-free photocatalyst for the photosynthetic production of H 2 O 2 in seawater. This catalyst exhibits high photocatalytic ability to produce H 2 O 2 with the yield of 1776 μmol g −1 h −1 ( λ  ≥ 420 nm; 34.8 mW cm −2 ) in real seawater, about 4.8 times higher than the pure polymer. Combining with in-situ photoelectrochemical and transient photovoltage analysis, the active site and the catalytic mechanism of this composite catalyst in seawater are also clearly clarified. This work opens up an avenue for a highly efficient and practical, available catalyst for H 2 O 2 photoproduction in real seawater. It is a challenge to produce hydrogen peroxide in seawater by photocatalysis. Here, the authors design and synthesize a metal-free photocatalyst based on carbon dots with a salt-protective electron sink effect, which exhibits enhanced hydrogen peroxide photoproduction in real seawater.

The external quantum efficiency of state-of-the-art quantum dot light-emitting diodes is limited by the low photon out-coupling efficiency. Light-emitting diodes using oriented nanostructures such as nanorods, nanoplatelets and dot-in-disc nanocrystals favour photon out-coupling; however, their internal quantum efficiency is often compromised and thus achieving a net gain has proved challenging. Here we report isotropic-shaped quantum dots featuring a mixed-crystallographic structure composed of wurtzite and zinc blende phases. The wurtzite phase promotes dipole–dipole interactions that orient quantum dots in solution-processed films, whereas the zinc blende phase helps lift the electronic state degeneracy to enable directional light emission. These combined features improve photon out-coupling without compromising internal quantum efficiency. Fabricated light-emitting diodes exhibit an external quantum efficiency of 35.6% and can be continuously operated with an initial brightness of 1,000 cd m – 2 for 4.5 years with a minimal performance loss of about 5%. Dipole–dipole interactions in mixed-phase CdZnSeS quantum dots enable the effective orientation of the quantum dots and improved photon out-coupling when employed in a light emitting diode.

Deformable full-colour light-emitting diodes with ultrafine pixels are essential for wearable electronics, which requires the conformal integration on curvilinear surface as well as retina-like high-definition displays. However, there are remaining challenges in terms of polychromatic configuration, electroluminescence efficiency and/or multidirectional deformability. Here we present ultra-thin, wearable colloidal quantum dot light-emitting diode arrays utilizing the intaglio transfer printing technique, which allows the alignment of red–green–blue pixels with high resolutions up to 2,460 pixels per inch. This technique is readily scalable and adaptable for low-voltage-driven pixelated white quantum dot light-emitting diodes and electronic tattoos, showing the best electroluminescence performance (14,000 cd m −2 at 7 V) among the wearable light-emitting diodes reported up to date. The device performance is stable on flat, curved and convoluted surfaces under mechanical deformations such as bending, crumpling and wrinkling. These deformable device arrays highlight new possibilities for integrating high-definition full-colour displays in wearable electronics. Deformable and high-resolution LEDs have attracted great interest for wearable electronics, but full-colour display is still challenging. Using a stamp printing technology, Choi et al . build ultra-thin RGB quantum dot pixel arrays with luminous efficiency of 14,000 cd m −2 operated at low voltage of 7 V.

The thermal quenching of light emission is a critical bottleneck that hampers the real-world application of lead halide perovskite nanocrystals in both electroluminescent and down-conversion light-emitting diodes. Here, we report CsPbBr3 perovskite nanocrystals with a temperature-independent emission efficiency of near unity and constant decay kinetics up to a temperature of 373 K. This unprecedented regime is obtained by a fluoride post-synthesis treatment that produces fluorine-rich surfaces with a wider energy gap than the inner nanocrystal core, yielding suppressed carrier trapping, improved thermal stability and efficient charge injection. Light-emitting diodes incorporating these fluoride-treated perovskite nanocrystals show a low turn-on voltage and spectrally pure green electroluminescence with an external quantum efficiency as high as 19.3% at 350 cd m−2. Importantly, nearly 80% of the room-temperature external quantum efficiency is preserved at 343 K, in contrast to the dramatic drop commonly observed for standard CsPbBr3 perovskite nanocrystal light-emitting diodes. These results provide a promising pathway for high-performance, practical light-emitting diodes based on perovskite nanostructures.Fluoride-treated CsPbBr3 nanocrystals emit light with near unity efficiency at temperatures of up to 373 K.

Light-emitting diodes (LEDs) based on perovskite quantum dots (QDs) have produced external quantum efficiencies (EQEs) of more than 25% with narrowband emission 1 , 2 , but these LEDs have limited operating lifetimes. We posit that poor long-range ordering in perovskite QD films—variations in dot size, surface ligand density and dot-to-dot stacking—inhibits carrier injection, resulting in inferior operating stability because of the large bias required to produce emission in these LEDs. Here we report a chemical treatment to improve the long-range order of perovskite QD films: the diffraction intensity from the repeating QD units increases three-fold compared with that of controls. We achieve this using a synergistic dual-ligand approach: an iodide-rich agent (aniline hydroiodide) for anion exchange and a chemically reactive agent (bromotrimethylsilane) that produces a strong acid that in situ dissolves smaller QDs to regulate size and more effectively removes less conductive ligands to enable compact, uniform and defect-free films. These films exhibit high conductivity (4 × 10 −4  S m −1 ), which is 2.5-fold higher than that of the control, and represents the highest conductivity recorded so far among perovskite QDs. The high conductivity ensures efficient charge transportation, enabling red perovskite QD-LEDs that generate a luminance of 1,000 cd m −2 at a record-low voltage of 2.8 V. The EQE at this luminance is more than 20%. Furthermore, the stability of the operating device is 100 times better than previous red perovskite LEDs at EQEs of more than 20%. Improving the long-range order of the quantum dots in perovskite LEDs can markedly enhance their operational stability.

With the ever-growing demand for a greater number of pixels, next-generation displays have challenging requirements for resolution as well as colour gamut. Here, to meet this need, quantum-dot light-emitting diodes (QLEDs) with an ultrahigh pixel resolution of 9,072–25,400 pixels per inch are realized via transfer printing combined with the Langmuir–Blodgett film technology. To reduce the leakage current of the devices, a honeycomb-patterned layer of wide-bandgap quantum dots is embedded between the light-emitting quantum-dot pixels as a non-emitting charge barrier layer. Red and green QLEDs are demonstrated. Notably, the red devices achieve a brightness of up to 262,400 cd m−2 at an applied voltage of 8 V and a peak external quantum efficiency of 14.72%. This work provides a promising way for achieving ultrahigh-resolution QLED devices with high performance.The demonstration of high-resolution quantum-dot light-emitting diodes by transfer printing could prove useful for next-generation displays.

Colloidal quantum dots (QDs) stand at the forefront of a variety of photonic applications given their narrow spectral bandwidth and near-unity luminescence efficiency. However, integrating luminescent QD films into photonic devices without compromising their optical or transport characteristics remains challenging. Here we devise a dual-ligand passivation system comprising photocrosslinkable ligands and dispersing ligands to enable QDs to be universally compatible with solution-based patterning techniques. The successful control over the structure of both ligands allows the direct patterning of dual-ligand QDs on various substrates using commercialized photolithography (i-line) or inkjet printing systems at a resolution up to 15,000 pixels per inch without compromising the optical properties of the QDs or the optoelectronic performance of the device. We demonstrate the capabilities of our approach for QD-LED applications. Our approach offers a versatile way of creating various structures of luminescent QDs in a cost-effective and non-destructive manner, and could be implemented in nearly all commercial photonics applications where QDs are used.A dual-ligand passivation system comprising photocrosslinkable ligands and dispersing ligands enables quantum dots to be universally compatible with solution-based patterning techniques.

Quantum dot (QD) light-emitting diodes (LEDs) are ideal for large-panel displays because of their excellent efficiency, colour purity, reliability and cost-effective fabrication 1 – 4 . Intensive efforts have produced red-, green- and blue-emitting QD-LEDs with efficiencies of 20.5 per cent 4 , 21.0 per cent 5 and 19.8 per cent 6 , respectively, but it is still desirable to improve the operating stability of the devices and to replace their toxic cadmium composition with a more environmentally benign alternative. The performance of indium phosphide (InP)-based materials and devices has remained far behind those of their Cd-containing counterparts. Here we present a synthetic method of preparing a uniform InP core and a highly symmetrical core/shell QD with a quantum yield of approximately 100 per cent. In particular, we add hydrofluoric acid to etch out the oxidative InP core surface during the growth of the initial ZnSe shell and then we enable high-temperature ZnSe growth at 340 degrees Celsius. The engineered shell thickness suppresses energy transfer and Auger recombination in order to maintain high luminescence efficiency, and the initial surface ligand is replaced with a shorter one for better charge injection. The optimized InP/ZnSe/ZnS QD-LEDs showed a theoretical maximum external quantum efficiency of 21.4 per cent, a maximum brightness of 100,000 candelas per square metre and an extremely long lifetime of a million hours at 100 candelas per square metre, representing a performance comparable to that of state-of-the-art Cd-containing QD-LEDs. These as-prepared InP-based QD-LEDs could soon be usable in commercial displays. A method of engineering efficient and stable InP/ZnSe/ZnS quantum dot light-emitting diodes (QD-LEDs) has improved their performance to the level of state-of-the-art cadmium-containing QD-LEDs, removing the problem of the toxicity of cadmium in large-panel displays.