Metastable structural polymorphs can have superior properties and applications to their thermodynamically stable phases, but the rational synthesis of metastable phases is a challenge. Here, a new strategy for stabilizing metastable phases using surface functionalization is demonstrated using the example of formamidinium lead iodide (FAPbI) perovskite, which is metastable at room temperature (RT) but holds great promises in solar and light-emitting applications. We show that, through surface ligand functionalization during direct solution growth at RT, pure FAPbI in the cubic perovskite phase can be stabilized in nanostructures and thin films at RT without cation or anion alloying. Surface characterizations reveal that long-chain alkyl or aromatic ammonium (LA) cations bind to the surface of perovskite structure. Calculations show that such functionalization reduces the surface energy and plays a dominant role in stabilizing the metastable perovskite phase. Excellent photophysics and optically pumped lasing from the stabilized single-crystal FAPbI nanoplates with low thresholds were demonstrated. High-performance solar cells can be fabricated with such directly synthesized stabilized phase-pure FAPbI with a lower bandgap. Our results offer new insights on the surface chemistry of perovskite materials and provide a new strategy for stabilizing metastable perovskites and metastable polymorphs of solid materials in general.

We report the fabrication of 2D ZnIn2S4 nanosheet/1D TiO2 nanorod heterojunction arrays by a facile hydrothermal process and their use as photoelectrodes in a photoelectrochemical (PEC) cell for high-performance solar water splitting. The morphology, microstructure, and phase of pristine TiO2 and 2D ZnIn2S4 nanosheet/1D TiO2 nanorod heterojunction arrays were characterized in detail. PEC measurements showed that 2D/1D heterojunction arrays offered enhanced photocurrent density (3 times higher than that of pristine TiO2), negatively shifted onset potential from 0.05 to -0.53 V, and high light on/off cycle stability. Electrochemical impedance investigation attested to a significant improvement of the interface electron transfer kinetics in this heterojunction, thus facilitating electron-hole separation, transfer, and collection, which resulted in enhanced PEC properties.

Organic–inorganic perovskite solar cells with a planar architecture have attracted much attention due to the simple structure and easy fabrication. However, the power conversion efficiency and hysteresis behavior need to be improved for planar‐type devices where the electron transport layer is vital. SnO2 is a promising alternative for TiO2 as the electron transport layer owing to the high charge mobility and chemical stability, but the hysteresis issue can still remain despite the use of SnO2. Now, a facile and effective method is presented to simultaneously tune the electronic property of SnO2 and passivate the defects at the interface between the perovskite and SnO2. The perovskite solar cells with ammonium chloride induced coagulated SnO2 colloids exhibit a power conversion efficiency of 21.38 % with negligible hysteresis, compared to 18.71 % with obvious hysteresis for the reference device. The device stability can also be significantly improved.

The realization of multiferroics in nanostructures, combined with a large electric dipole and ferromagnetic ordering, could lead to new applications, such as high-density multistate data storage. Although multiferroics have been broadly studied for decades, ferromagnetic ferroelectricity is rarely explored, especially in two-dimensional (2D) systems. Here we report the discovery of 2D ferromagnetic ferroelectricity in layered transition-metal halide systems. On the basis of first-principles calculations, we reveal that a charged CrBr_{3} monolayer exhibits in-plane multiferroicity, which is ensured by the combination of orbital and charge ordering as realized by the asymmetric Jahn-Teller distortions of octahedral Cr─Br_{6} units. As an example, we further show that (CrBr_{3})_{2}Li is a ferromagnetic ferroelectric multiferroic. The explored phenomena and mechanism of multiferroics in this 2D system not only are useful for fundamental research in multiferroics but also enable a wide range of applications in nanodevices.

CdS nanostructures have received much attention in recent years as building blocks for optoelectronic devices due to their unique physical and chemical properties. This progress report provides an overview of recent research about rational design of CdS nanoscale photodetectors. Three kinds of photodetectors according to the metal-semiconductor contact types are discussed in detail: Ohmic contact, Schottky contact, and field enhanced transistor configuration. The focus is on the tuning of optical and electrical properties CdS nanostructures by element doping, composition and bandgap engineering, and heterojunction integration, along with thus modified device performances generated during these tuning processes. Latest concepts of photodetector design such as flexible, self-powered, plasmonic, and piezophototronic photodetectors with novel properties are introduced to demonstrate the future directions of such an exciting research field.

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Through systematic molecular dynamics simulations we theoretically investigate the potential applications of hexagonal boron nitride (h-BN) for seawater desalination. Our results indicate that the rationally designed h-BN membranes have great permeability, selectivity, and controllability for water desalination. The size and chemistry of the pores are shown to play an important role in regulating the water flux and salt rejection. Pores with only nitrogen atoms on the edges have higher fluxes than the boron-lined pores. In particular, two-dimensional h-BN with medium-sized N4 pores show 100% salt rejection with outstanding water permeability, which is several orders of magnitude higher than that of conventional reverse osmosis membranes. Furthermore, we study the mechanical strain effect on the desalination performance of monolayer h-BN with relatively small N3 pores, suggesting that water flux and salt rejection can be precisely tuned by tensile strain. The findings in the present work unambiguously propose that porous boron nitride nanosheets are quite promising as new functional membranes for water desalination.

The unprecedented applications of two-dimensional (2D) atomic sheets in spintronics are formidably hindered by the lack of ordered spin structures. Here we present first-principles calculations demonstrating that the recently synthesized dimethylmethylene-bridged triphenylamine (DTPA) porous sheet is a ferromagnetic half-metal and that the size of the band gap in the semiconducting channel is roughly 1 eV, which makes the DTPA sheet an ideal candidate for a spin-selective conductor. In addition, the robust half-metallicity of the 2D DTPA sheet under external strain increases the possibility of applications in nanoelectric devices. In view of the most recent experimental progress on controlled synthesis, organic porous sheets pave a practical way to achieve new spintronics.