Anisotropy of Anion Diffusion in All-Inorganic Perovskite Single Crystals.

Ion diffusion is a fundamentally important process in understanding and manipulating the optoelectronic properties of semiconductors. Most current studies on ionic diffusion have been focusing on perovskite polycrystalline thin films and nanocrystals. However, the random orientation and grain boundaries can heavily interfere with the kinetics of ion diffusion, where the experimental results only reveal the average ion exchange kinetics and the actual ion diffusion mechanisms perpendicular to the direction of individual crystal facets remain unclear. Here, the anion (Cl, I) diffusion anisotropy on (111) and (100) facets of CsPbBr3 single crystals is demonstrated. The as-grown single crystals with (111) and (100) facets exhibit anisotropic growth with different halide incorporation, which lead to different resulting optoelectronic properties. Combined experimental characterizations and theoretical calculations reveal that the (111) CsPbBr3 shows a faster anion diffusion behavior compared with that of the (100) CsPbBr3, with a lower diffusion energy barrier, a larger built-in electric field, and lower inverse defect formation energy. The work highlights the anion diffusion anisotropic mechanisms perpendicular to the direction of individual crystal facets for optimizing and designing perovskite optoelectronic devices.

Sizeable square CsPb2Br5 nanosheets for photodetection.

All-inorganic perovskites have garnered significant attention in optoelectronics. Herein, square CsPb2Br5 nanosheets, with lateral dimensions of up to 200 µm and a thickness of less than 50 nm, were successfully synthesized via a straightforward aqueous method using HBr as a morphology-tailoring agent. A photodetector composed of a single nanosheet was subsequently fabricated and exhibited remarkable photodetection capabilities, demonstrating a detectivity of 5.98 × 109 Jones. These findings offer new perspectives on the synthesis and utilization of CsPb2Br5 and other perovskite nanostructures in optoelectronic devices.

Nitrogen-doped hollow carbon@tin disulfide as a bipolar dynamic host for lithium-sulfur batteries with enhanced kinetics and cyclability.

Lithium-sulfur batteries (LSBs) are promising next-generation electrochemical energy storage systems owing to high theoretical specific capacity (1675 mAh/g) and low cost. However, the shuttling effect of soluble polysulfides with slow conversion kinetics has deferred their commercial applications. The feasible design and synthesis of composite cathode hosts offer a promise solution to improving their electrochemical performances. In this work, tin disulfide (SnS2) nanosheets were anchored on nitrogen-doped hollow carbon with mesoporous shells, forming a bipolar dynamic host ("SnS2@NHCS"). It can efficiently confine the polysulfides and promote their conversion during (dis)charge. The as-assembled LSBs delivered a high capacity, superior rate and cyclability. This work presents a new view on the exploration of novel composite electrode materials for various rechargeable batteries with emerging applications.

Engineering electronic structures and optical properties of a MoSi2N4 monolayer via modulating surface hydrogen chemisorption.

Recently, a MoSi2N4 monolayer has been successfully synthesized by a delicately designed chemical vapor deposition (CVD) method. It exhibits promising (opto)electronic properties due to a relatively narrow bandgap (∼1.94 eV), high electron/hole mobility, and excellent thermal/chemical stability. Currently, much effort is being devoted to further improving its properties through engineering defects or constructing nanocomposites (e.g., van der Waals heterostructures). Herein, we report a theoretical investigation on hydrogenation as an alternative surface functionalization approach to effectively manipulate its electronic structures and optical properties. The calculation results suggested that chemisorption of H atoms on the top of N atoms on MoSi2N4 was energetically most favored. Upon H chemisorption, the band gap values gradually decreased from 1.89 eV (for intrinsic MoSi2N4) to 0 eV (for MoSi2N4-16H) and 0.25 eV (for MoSi2N4-32H), respectively. The results of optical properties studies revealed that a noticeable enhancement in light absorption intensity could be realized in the visible light range after the surface hydrogenation process. Specifically, full-hydrogenated MoSi2N4 (MoSi2N4-32H) manifested a higher absorption coefficient than that of semi-hydrogenated MoSi2N4 (MoSi2N4-16H) in the visible light range. This work can provide theoretical guidance for rational engineering of optical and optoelectronic properties of MoSi2N4 monolayer materials via surface hydrogenation towards emerging applications in electronics, optoelectronics, photocatalysis, etc.

Mesoporous Pt@Pt-skin Pt3Ni core-shell framework nanowire electrocatalyst for efficient oxygen reduction.

The design of Pt-based nanoarchitectures with controllable compositions and morphologies is necessary to enhance their electrocatalytic activity. Herein, we report a rational design and synthesis of anisotropic mesoporous Pt@Pt-skin Pt3Ni core-shell framework nanowires for high-efficient electrocatalysis. The catalyst has a uniform core-shell structure with an ultrathin atomic-jagged Pt nanowire core and a mesoporous Pt-skin Pt3Ni framework shell, possessing high electrocatalytic activity, stability and Pt utilisation efficiency. For the oxygen reduction reaction, the anisotropic mesoporous Pt@Pt-skin Pt3Ni core-shell framework nanowires demonstrated exceptional mass and specific activities of 6.69 A/mgpt and 8.42 mA/cm2 (at 0.9 V versus reversible hydrogen electrode), and the catalyst exhibited high stability with negligible activity decay after 50,000 cycles. The mesoporous Pt@Pt-skin Pt3Ni core-shell framework nanowire configuration combines the advantages of three-dimensional open mesopore molecular accessibility and compressive Pt-skin surface strains, which results in more catalytically active sites and weakened chemisorption of oxygenated species, thus boosting its catalytic activity and stability towards electrocatalysis.

All-Inorganic Perovskite Single-Crystal Photoelectric Anisotropy.

Engineering surface structure can precisely and effectively tune the optoelectronic properties of halide perovskites, but are incredibly challenging. Herein, the design and fabrication of uniform all-inorganic CsPbBr3 cubic/tetrahedral single-crystals are reported with precise control of the (100) and (111) surface anisotropy, respectively. By combining with theoretical calculations, it is demonstrated that the preferred (100) surface engineering of the CsPbBr3 single-crystals enables a lowest surface bandgap energy (2.33 eV) and high-rate carrier mobility up to 241 µm2  V-1  s-1 , inherently boosting their light-harvesting and carrier-transport capability. Meanwhile, the polar (111) surface induces ≈0.16 eV upward surface-band bending and ultrahigh surface defect density of 1.49 × 1015  cm-3 , which is beneficial for enhancing surface-defects-catalyzed reactions. The work highlights the anisotropic surface engineering for boosting perovskite optoelectronic devices and beyond.