Solid-state light-emitting devices based on direct-bandgap semiconductors have, over the past two decades, been utilized as energy-efficient sources of lighting. However, fabrication of these devices typically relies on expensive high-temperature and high-vacuum processes, rendering them uneconomical for use in large-area displays. Here, we report high-brightness light-emitting diodes based on solution-processed organometal halide perovskites. We demonstrate electroluminescence in the near-infrared, green and red by tuning the halide compositions in the perovskite. In our infrared device, a thin 15 nm layer of CH3NH3PbI(3-x)Cl(x) perovskite emitter is sandwiched between larger-bandgap titanium dioxide (TiO2) and poly(9,9'-dioctylfluorene) (F8) layers, effectively confining electrons and holes in the perovskite layer for radiative recombination. We report an infrared radiance of 13.2 W sr(-1) m(-2) at a current density of 363 mA cm(-2), with highest external and internal quantum efficiencies of 0.76% and 3.4%, respectively. In our green light-emitting device with an ITO/PEDOT:PSS/CH3NH3PbBr3/F8/Ca/Ag structure, we achieved a luminance of 364 cd m(-2) at a current density of 123 mA cm(-2), giving external and internal quantum efficiencies of 0.1% and 0.4%, respectively. We show, using photoluminescence studies, that radiative bimolecular recombination is dominant at higher excitation densities. Hence, the quantum efficiencies of the perovskite light-emitting diodes increase at higher current densities. This demonstration of effective perovskite electroluminescence offers scope for developing this unique class of materials into efficient and colour-tunable light emitters for low-cost display, lighting and optical communication applications.

Solar cells comprising methylammonium lead iodide perovskite (MAPI) are notorious for their sensitivity to moisture. We show that hydrated crystal phases are formed when MAPI is exposed to water vapour at room temperature and that these phase changes are fully reversed when the material is subsequently dried. The reversible formation of CH 3 NH 3 PbI 3 •H 2 O followed by (CH 3 NH 3 ) 4 PbI 6 •2H 2 O (upon long exposure times) was observed using time resolved XRD and ellipsometry of thin films prepared using 'solvent engineering', single crystals, and state of the art solar cells. In contrast to water vapour, the presence of liquid water results in the irreversible decomposition of MAPI to form PbI 2 . MAPI changes from dark brown to transparent on hydration; the precise optical constants of CH 3 NH 3 PbI 3 •H 2 O formed on single crystals were determined, with a bandgap at 3.1 eV. Using the single crystal optical constants and thin film ellipsometry measurements, the time dependent changes to MAPI films exposed to moisture were modelled. The results suggest that the mono-hydrate phase forms independently of the depth in the film suggesting rapid transport of water molecules along grain boundaries. Vapour phase hydration of an unencapsulated solar cell (initially J sc ≈ 19 mA cm -2 and V oc ≈ 1.05 V at 1 sun) resulted in more than a 90 % drop in short circuit photocurrent and around 200 mV loss in open circuit potential, but these losses were fully reversed after the cell was exposed to dry nitrogen for 6 hours. Hysteresis in the current-voltage characteristics was significantly increased after this dehydration, which may be related to changes in the defect density and morphology of MAPI following recrystallization from the hydrate. Based on our observations we suggest that irreversible decomposition of MAPI in the presence of water vapour only occurs significantly once a grain has been fully converted to the hydrate phase.

Double-ended aryl dithiols [alpha,alpha'-xylyldithiol (XYL) and 4,4'-biphenyldithiol] formed self-assembled monolayers (SAMs) on gold(111) substrates and were used to tether nanometer-sized gold clusters deposited from a cluster beam. An ultrahigh-vacuum scanning tunneling microscope was used to image these nanostructures and to measure their current-voltage characteristics as a function of the separation between the probe tip and the metal cluster. At room temperature, when the tip was positioned over a cluster bonded to the XYL SAM, the current-voltage data showed "Coulomb staircase" behavior. These data are in good agreement with semiclassical predictions for correlated single-electron tunneling and permit estimation of the electrical resistance of a single XYL molecule (approximately18 ± 12 megohms).

Covalent organic frameworks (COFs) are crystalline porous polymers formed by a bottom‐up approach from molecular building units having a predesigned geometry that are connected through covalent bonds. They offer positional control over their building blocks in two and three dimensions. This control enables the synthesis of rigid porous structures with a high regularity and the ability to fine‐tune the chemical and physical properties of the network. This Feature Article provides a comprehensive overview over the structures realized to date in the fast growing field of covalent organic framework development. Different synthesis strategies to meet diverse demands, such as high crystallinity, straightforward processability, or the formation of thin films are discussed. Furthermore, insights into the growing fields of COF applications, including gas storage and separations, sensing, electrochemical energy storage, and optoelectronics are provided.

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Nanosized mesoporous silica particles with high colloidal stability attract growing attention as drug delivery systems for targeted cancer treatment and as bioimaging devices. This Perspective describes recent breakthroughs in mesoporous silica nanoparticle design to demonstrate their high potential as multifunctional drug delivery nanocarriers. These types of nanoparticles can feature a well-defined and tunable porosity at the nanometer scale, high loading capacity, and multiple functionality for targeting and entering different types of cells. We focus on the requirements for an efficient stimuli-responsive and thus controllable release of cargo into cancer cells and discuss design principles for smart and autonomous nanocarrier systems. Mesoporous silica nanoparticles are viewed as a promising and flexible platform for numerous biomedical applications.

Cs2AgBiBr6 double perovskite thin films were prepared and incorporated into photovoltaic devices featuring power conversion efficiencies close to 2.5%.

Conducting filaments of polyaniline have been prepared in the 3-nanometer-wide hexagonal channel system of the aluminosilicate MCM-41. Adsorption of aniline vapor into the dehydrated host, followed by reaction with peroxydisulfate, leads to encapsulated polyaniline filaments. Spectroscopic data show that the filaments are in the protonated emeraldine salt form, and chromatography indicates chain lengths of several hundred aniline rings. The filaments have significant conductivity while encapsulated in the channels, as measured by microwave absorption at 2.6 gigahertz. We have demonstrated previously the encapsulation of several different conjugated polymers such as polypyrrole and pyrolyzed polyacrylonitrile in the well-defined channels of zeolite molecular sieves (7-10). The template synthesis of conducting polymers in the much larger, random pores (about 0.1 to 1 pm) of insulating host membranes has also been described (11). Networks of poly(3-methylthiophene) dendrites have been grown between electrodes (12). We have now achieved the stabilization of conducting polyaniline filaments in the ordered, 3-nm-wide hexagonal channels of the mesoporous aluminosilicate host (13, 14) MCM-41. We were able to demonstrate the ac conductivity of such encapsulated filaments of nanometer dimensions.A distinctive feature of polyaniline among the conducting polymers is that its conductivity is not only controlled by the degree of chain oxidation but also by the level of protonation in {l (-B-NH-B-NH-)y (-B-N=Q=N-)1-yl (HA)Q,, (15,16 (Fig. 2). The similarity of the ring and C-H bending modes between PANI-loaded host (PANI-MCM) and emeraldine salt, seen in their Raman spectra (Fig. 3) 4.6, 3.4 (shoulder), and 1.6 eV, typical for the band-gap and polaron transitions of emeraldine salt (20). The encapsulated, evacuated polymer shows a single, fairly broad (8 G) electron spin resonance line at g = 2.0032, suggesting slightly lower protonation levels than in emeraldine salt (21) or dipolar interactions with the MCM channel walls.The relative chain length of intrachannel polyaniline [versus polystyrene (PS) (Fig. 4). If we assume a polymer density of 1.3 g/cm3 (23), the loading of 0.28 g per gram of host closely corresponds to the change in poros- Fig. 1. Reaction scheme for the encapsulation of polyaniline in the channels of