Concerns about the toxicity of lead-based perovskites have aroused great interest for the development of alternative lead-free perovskite-type materials. Recently, theoretical calculations predict that Pb 2+ cations can be substituted by a combination of Cu 2+ and Sb 3+ cations to form a vacancy-ordered layered double perovskite structure with superior optoelectronic properties. However, accessibilities to this class of perovskite-type materials remain inadequate, hindering their practical implementations in various applications. Here, we report the first colloidal synthesis of Cs 4 CuSb 2 Cl 12 perovskite-type nanocrystals (NCs). The resulting NCs exhibit a layered double perovskite structure with ordered vacancies and a direct band gap of 1.79 eV. A composition−structure−property relationship has been established by investigating a series of Cs 4 Cu x Ag 2−2x Sb 2 Cl 12 perovskite-type NCs (0 ≤ x ≤ 1). The composition induced crystal structure transformation, and thus, the electronic band gap evolution has been explored by experimental observations and further confirmed by theoretical calculations. Taking advantage of both the unique electronic structure and solution processability, we demonstrate that the Cs 4 CuSb 2 Cl 12 NCs can be solution-processed as high-speed photodetectors with ultrafast photoresponse and narrow bandwidth. We anticipate that our study will prompt future research to design and fabricate novel and high-performance lead-free perovskite-type NCs for a range of applications.

Photocatalytic water splitting has received much attention for the production of renewable hydrogen from water, and two-dimensional (2D) materials show great potential for use as efficient photocatalysts. In this paper, the stabilities and electronic and optical properties of Janus group-III monochalcogenide M2XY (M = Ga and In and X/Y = S, Se, and Te) monolayers were investigated using first-principles calculations. The band gaps of the Janus M2XY monolayers are in the range of 1.54–2.98 eV, which satisfies the minimum band gap requirement of photocatalysts for overall water splitting. Indirect-to-direct band gap transitions occur in the M2XTe (M = Ga and In and X = S and Se) monolayers. These transitions were induced by the valence band maximum at the Γ point, being composed of the p x and p y orbitals of the M and Y atoms in M2XTe instead of the p z orbitals of the M and X atoms in the MX and other M2XY monolayers. The Janus M2XY monolayers have a considerable optical absorption coefficient (∼3 × 104/cm) in the visible light region and an even larger absorption coefficient (∼105/cm) in the near ultraviolet region. This study not only highlights the efficient photocatalytic performance of the 2D MX and M2XY monolayers but also provides an approach for tuning the band structures of 2D photocatalysts by forming Janus structures.

Semiconductor quantum dots (QDs) have attracted tremendous attention in the field of photocatalysis, owing to their superior optoelectronic properties for photocatalytic reactions, including high absorption coefficients and long photogenerated carrier lifetimes. Herein, by choosing 2‐(3,4‐dimethoxyphenyl)‐3‐oxobutanenitrile as a model substrate, we demonstrate that the stereoselective (>99 %) C−C oxidative coupling reaction can be realized with a high product yield (99 %) using zwitterionic ligand capped CsPbBr3 perovskite QDs under visible light illumination. The reaction can be generalized to different starting materials with various substituents on the phenyl ring and varied functional moieties, producing stereoselective dl‐isomers. A radical mediated reaction pathway has been proposed. Our study provides a new way of stereoselective C−C oxidative coupling via a photocatalytic means using specially designed perovskite QDs.

The mechanical and electronic properties of Janus monolayer transition metal dichalcogenides MXY (M  =  Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W; X/Y  =  S, Se, Te) were investigated using density functional theory. Results show that breaking the out-of-plane structural symmetry can be used to tune the electronic and mechanical behavior of monolayer transition metal dichalcogenides. The band gaps of monolayer WXY and MoXY are in the ranges of 0.16-1.91 and 0.94-1.69 eV, respectively. A semiconductor to metallic phase transition occurred in Janus monolayer MXY (M  =  Ti, Zr and Hf). The monolayers MXY (M  =  V, Nb, Ta and Cr) show metallic characteristics, which show no dependence on the structural symmetry breaking. The mechanical properties of MXY depended on the composition. Monolayer MXY (M  =  Mo, Ti, Zr, Hf and W) showed brittle characteristic, whereas monolayer CrXY and VXY are with ductile characteristic. The in-plane stiffness of pristine and Janus monolayer MXY are in the range between 22 and 158 N m. The tunable electronic and mechanical properties of these 2D materials would advance the development of ultra-sensitive detectors, nanogenerators, low-power electronics, and energy harvesting and electromechanical systems.

Lead-free perovskites and their analogues have been extensively studied as a class of next-generation luminescent and optoelectronic materials. Herein, we report a new synthesis of colloidal Cs4M(II)Bi2Cl12 (M(II) = Cd,...

Janus transition-metal dichalcogenides have been predicted to be promising candidates for hydrogen evolution reaction (HER) due to their inherent structural asymmetry. However, the effect of intrinsic defects, including vacancies, antisites, and grain boundaries, on their catalytic activity is still unknown. MoSSe provides an ideal platform for studying such defects, since theoretical calculation has indicated that the formation energies of point defects and grain boundaries on MoSSe were lower than that of pristine MoS2 monolayer. In this work, density functional theory is utilized to study all of the possible intrinsic defects on the MoSSe monolayer for HER. The MoSSe monolayer with 4|4, 4|8a, 5|7b, 8|10a GBs, vacancies (VS, VSe, VSSe, VMo, VMoS3 ), and antisite defects (MoSSe, SeMo, SMo) shows enhanced HER performance. The adsorption behavior of hydrogen on defects were explained by using a “states-filling” model. The adsorption energy of hydrogen during catalysis changes linearly with the work required to fill unoccupied electronic states within the catalysts. This work could provide a more comprehensive understanding of all of the possible active sites of Janus transition-metal dichalcogenides for HER.

Lead‐free double perovskites have emerged as a promising class of materials with potential to be integrated into a wide range of optical and optoelectronic applications. Herein, the first synthesis of 2D Cs2AgInxBi1‐xCl6 (0 ≤ x ≤ 1) alloyed double perovskite nanoplatelets (NPLs) with well controlled morphology and composition is demonstrated. The obtained NPLs show unique optical properties with the highest photoluminescence quantum yield of 40.1%. Both temperature dependent spectroscopic studies and density functional theory calculation results reveal that the morphological dimension reduction and In–Bi alloying effect together boost the radiative pathway of the self‐trapped excitons of the alloyed double perovskite NPLs. Moreover, the NPLs exhibit good stability under ambient conditions and against polar solvents, which is ideal for all solution‐processing of the materials in low‐cost device manufacturing. The first solution‐processed light‐emitting diodes is demonstrated using the Cs2AgIn0.9Bi0.1Cl6 alloyed double perovskite NPLs as the sole emitting component, showing luminance maximum of 58 cd m−2 and peak current efficiency of 0.013 cd A−1. This study sheds light on morphological control and composition‐property relationships of double perovskite nanocrystals, paving the way toward ultimate utilizations of lead‐free perovskite materials in diverse sets of real‐life applications.

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