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The performance of quasi-2D perovskite light emitting diodes (LEDs) with mixed small cations, cesium and formamidinium (FA), is significantly affected by their ratio. The best devices obtained for Cs:FA ratio of 1:1 exhibit a maximum external quantum efficiency (EQE) of 12.1%, maximum luminance of 15 070 cd m−2 and maximum current efficiency of 46.1 cd A−1, which is significantly higher (about 3 times) compared to devices with FA only (maximum EQE of 4.1%, maximum luminance of 4521 cd m−2) and Cs-only (maximum EQE of 4.0%, maximum luminance of 4886 cd m−2). The photoluminescence quantum yield of the Cs:FA 1:1 sample is similarly enhanced, 21.3% compared 5.4% and 6%, for FA-only and Cs-only samples, respectively. It can be observed that the Cs:FA ratio significantly affects the crystallization of the perovskite, with the optimal 1:1 ratio resulting in the formation of tetragonal Cs0.5FA0.5PbBr3 phase (different from cubic FAPbBr3 and orthorhombic CsPbBr3) with pronounced preferential orientation as well as a significant reduction in the trap density, which leads to a substantial improvement in the light- emitting performance.

Bismuth chalcogenides are promising materials for thermoelectric (TE) application due to their high power factor (product of the square of the Seebeck coefficient and electrical conductivity). However, their high thermal conductivity is an issue of concern. Single doping has proven to be useful in improving TE performance in recent years. Here, it is shown that dual isovalent doping shows the synergistic effect of thermal conductivity reduction and electron density control. The insertion of large atoms in the layered Bi2Te3 structure distorts the crystal lattice and contributes significantly to phonon scattering. The ultralow thermal conductivity (KT = 0.35 W m−1 K−1 at 473 K) compensates for the low power factor and thus enhances TE performance. The density functional theory electronic structure calculation results reveal deep defects states in the valence band, which influences the electronic transport properties of the system. Therefore, the dual dopants (indium and antimony) show a coupled effect of improvement in the density of state near the Fermi level and reduction in the conduction band minimum, thus enhancing electron density. Numerically, it is demonstrated that the dual doping favors acoustic phonon scattering and thus drastically reduces the thermal conductivity.

An ionic-liquid-based Zn salt electrolyte is demonstrated to be an effective route to solve both the side-reaction of the hydrogen evolution reaction (HER) and Zn-dendrite growth in Zn-ion batteries. The developed electrolyte enables hydrogen-free, dendrite-free Zn plating/stripping over 1500 h cycle (3000 cycles) at 2 mA cm-2 with nearly 100% coulombic efficiency. Meanwhile, the oxygen-induced corrosion and passivation are also effectively suppressed. These features bring Zn-ion batteries an unprecedented long lifespan over 40 000 cycles at 4 A g-1 and high voltage of 2.05 V with a cobalt hexacyanoferrate cathode. Furthermore, a 28.6 µm thick solid polymer electrolyte of a poly(vinylidene fluoride-hexafluoropropylene) film filled with poly(ethylene oxide)/ionic-liquid-based Zn salt is constructed to build an all-solid-state Zn-ion battery. The all-solid-state Zn-ion batteries show excellent cycling performance of 30 000 cycles at 2 A g-1 at room temperature and withstand high temperature up to 70 °C, low temperature to -20 °C, as well as abuse test of bending deformation up to 150° for 100 cycles and eight times cutting. This is the first demonstration of an all-solid-state Zn-ion battery based on a newly developed electrolyte, which meanwhile solves the deep-seated hydrogen evolution and dendrite growth problem in traditional Zn-ion batteries.

A novel, facile, self-assembly approach, based on a gas-bubble-template model and assisted by graphene oxide, is developed to fabricate hollow 3D mesoporous CoFe2O4 nanospheres (NSs) and graphene composites. During the hydrothermal process, the oxygen-containing functional groups and defect sites on the graphene sheets act as nucleation centers to anchor released gas bubbles, providing a soft template for the aggregation of nanosized CoFe2O4 crystallite building blocks to form NSs. Benefiting from the synergistic effect between the hollow 3D mesoporous CoFe2O4 NSs and graphene, the electrode exhibited remarkable electrochemical performance with a high reversible capacity (≈1030 mA h g−1 after 60 cycles at 100 mA g−1), enhanced rate capability (≈970, ≈850, ≈555 mA h g−1 at 100, 500, 5000 mA g−1, respectively), and superior cyclic stability (≈805 mA h g−1 after 305 cycles at 2000 mA g−1 with a high coulombic efficiency of ≈99.5 %); these composites are thus high-performance anode materials for lithium ion batteries.

We have studied the properties of organic and organometallic polymers based on a similar chemical structure to elucidate the influence of the metal center on the optical and electronic properties of the polymers as well as their photovoltaic performance. Detailed characterization of the optical properties of both polymers is performed and film morphology and photovoltaic performance are compared. Metal-containing polymers exhibit red-shifted absorption and under optimal processing conditions exhibit different film morphology compared with the metal-free ones. Our results indicate that organometallic polymers represent a promising class of compounds for improved performance in photovoltaic cells.

Bundles of homogeneously alloyed Cu 2 − x (S y Se 1 − y ) nanowires with various compositions (0 ≤ y ≤ 1) are controllably prepared via a simple water-evaporation method under mild conditions. It is found that the nanowire bundles have similar copper contents (0.37 ≤ x ≤ 0.44) and morphologies, and the same face centered cubic (fcc) crystal structure and growth orientation of [110] over the entire composition range of y . To the best of the authors’ knowledge, this is the fi rst report on cubic phased ternary Cu 2 − x (S y Se 1 − y ) compounds. It is found that lattice parameter of the Cu 2 − x (Sy Se 1 − y ) compound changes linearly with the S content. It is also shown that the direct and the indirect bandgaps of the nanowires vary quadratically with the S content and have bowing parameters of 0.20 and 0.21 eV respectively. Energy-gap-tuning via compositional change is achieved for both the direct (1.48 − 1.87 eV) and the indirect (0.50 − 0.90 eV) bandgaps. The trends of lattice parameter and bandgap variations are consistent with those described by Vegard’s Law.

Zinc oxide arrays of conical and hexagonal back-tapered nanocolumns with well-developed, flat and horizontal (0001) facets were synthesized on gold-coated (100) silicon substrates by a thermal evaporation process. Evolution of these conical and back-tapered structures was investigated by analysis of their morphological and chemical structures in different growth phases employing scanning electron microscopy, energy-dispersive X-ray spectroscopy and cathodoluminescence imaging. This study reveals that an ultrathin gold film predeposited on silicon is required to provide nucleation sites and form ZnO grains that progressively grow to vertical nanostructures. The growth process is assisted by carbon-reduced zinc droplets deposited from the gas phase on the ZnO grains that evolve into back-tapered nanocanonical and hexagonal columns. These nanostructures are shown to be effective in the degradation of organic dyes. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Znx Cd1-x S single-crystal nanoribbons of controlled composition (where 0 ≤ x ≤ 1) can be synthesized by combining laser ablation with thermal evaporation. The nanoribbons exhibit lasing emission that can be continuously tuned within the ranges of 340-390 nm and 485-515 nm. These results suggest that Znx Cd1-x S nanoribbon lasers of pre-selected "tunable" wavelengths between 340 and 515 nm may be achievable by tailoring the value of x.

Arrays of well-aligned single-crystal zinc oxide (ZnO) nanowires of uniform diameter and length have been synthesized on a (100) silicon substrate via a simple horizontal double-tube system using chemical vapor transport and condensation method. X-ray diffraction and transmission electron microscopy (TEM) characterizations showed that the as-grown nanowires had the single-crystal hexagonal wurtzite structure with detectable defects and a growth direction. Raman spectra revealed phonon confinement effect when compared with those of ZnO bulk powder, nanoribbons, and nanoparticles. Photoluminescence exhibited strong ultraviolet emission at 3.29 eV under 355 nm excitation and green emission at 2.21 eV under 514.5 nm excitation. No catalyst particles were found at the tip of the nanowires, suggesting that the growth mechanism followed a self-catalyzed and saturated vapor–liquid–solid (VLS) model. Self-alignment of nanowires was attributed to the local balance and steady state of vapor flow at the substrate. The growth technique would be of particular interest for direct integration in the current silicon-technology-based optoelectronic devices.

Semiconductor-sensitized solar cells (SSCs) are emerging as promising devices for achieving efficient and low-cost solar-energy conversion. The recent progress in the development of ZnO-nanostructure-based SSCs is reviewed here, and the key issues for their efficiency improvement, such as enhancing light harvesting and increasing carrier generation, separation, and collection, are highlighted from aspects of surface-engineering techniques. The impact of other factors such as electrolyte and counter electrodes on the photovoltaic performance is also addressed. The current challenges and perspectives for the further advance of ZnO-based SSCs are discussed.

Research Grants Council of Hong Kong SAR, China [CityU101608]; City University of Hong Kong [7002275]; National Basic Research Program of China [2006CB933000, 2007CB936000]; National Natural Science Foundation of China [50825304, 50903059]