Synthesis of Lead‐free CsGeI3 Perovskite Colloidal Nanocrystals and Electron Beam‐induced Transformations

Colloidal nanocrystals (NCs) of metal halide perovskite have recently aroused great research interest, due to their remarkable optical and electronic properties. We report a solution synthesis of a new member in this category, that is, all‐inorganic lead‐free cesium germanium iodine (CsGeI₃) perovskite NCs. These CsGeI₃ colloidal NCs are confirmed to adopt a rhombohedral structure. Moreover, the electron beam‐induced transformations of these lead‐free perovskite NCs have been investigated for the first time. The fracture of single‐crystalline CsGeI₃ nanocubes occurs first, followed by the emergence and growth of cesium iodine (CsI) single crystals and the final fragmentation into small debris with random orientations. Notably, the electron‐reduced Ge species in CsGeI₃ nanocubes exhibit a distinctive transformation path, compared to heavier Pb atoms in lead halide perovskite NCs.     

Lead‐Free Halide Perovskite Nanocrystals: Crystal Structures,Synthesis, Stabilities,and Optical Properties

In recent years, there have been rapid advances in the synthesis of lead halide perovskite nanocrystals (NCs) for use in solar cells, light emitting diodes, lasers, and photodetectors. These compounds have a set of intriguing optical, excitonic, and charge transport properties, including outstanding photoluminescence quantum yield (PLQY) and tunable optical band gap. However, the necessary inclusion of lead, a toxic element, raises a critical concern for future commercial development. To address the toxicity issue, intense recent research effort has been devoted to developing lead‐free halide perovskite (LFHP) NCs. In this Review, we present a comprehensive overview of currently explored LFHP NCs with an emphasis on their crystal structures, synthesis, optical properties, and environmental stabilities (e.g., UV, heat, and moisture resistance). In addition, strategies for enhancing optical properties and stabilities of LFHP NCs as well as the state‐of‐the‐art applications are discussed. With the perspective of their properties and current challenges, we provide an outlook for future directions in this rapidly evolving field to achieve high‐quality LFHP NCs for a broader range of fundamental research and practical applications.     

Electron Beam‐Based Functionalization of Poly(ethersulfone) Membranes

Poly(ethersulfone) membranes were surface modified in a one‐step procedure. For this purpose, the membranes were soaked with aqueous solutions of different low‐molecular weight molecules bearing diverse hydrophilic functionalities and subject to electron beam treatment. No catalysts, photoinitiators, organic solvents or other toxic reagents were used, and no additional synthetic or purification steps were required.

     

Near‐Unity Photoluminescence Quantum Efficiency for All CsPbX3 (X=Cl,Br, and I) Perovskite Nanocrystals: A Generic Synthesis Approach

In a generic synthesis approach, all three CsPbX₃ (X=Cl, Br and I) perovskite nanocrystals having near unity quantum yields is reported. This has been achieved by injecting the desired amount of preformed alkylammonium halide salts which acted as a dual source providing halide ions and the capping agent to an equimolar amount of non‐halide Pb and Cs precursors in a reaction flask at an optimized reaction temperature. The composition sensitivity of Pb to Cs ratio, high temperature reaction, and injection of ammonium halide remained the key parameters for obtaining the high quantum yields. Details of the reaction process, use of different reagents and setting up the reaction parameters are reported.     

Colloidal Synthesis and Charge‐Carrier Dynamics of Cs2AgSb1−yBiyX6 (X: Br,Cl; 0 ≤y ≤1) Double Perovskite Nanocrystals

A series of lead‐free double perovskite nanocrystals (NCs) Cs₂AgSb_1?yBi_yX₆ (X: Br, Cl; 0≤y≤1) is synthesized. In particular, the Cs₂AgSbBr₆ NCs is a new double perovskite material that has not been reported for the bulk form. Mixed Ag–Sb/Bi NCs exhibit enhanced stability in colloidal solution compared to Ag–Bi or Ag–Sb NCs. Femtosecond transient absorption studies indicate the presence of two prominent fast trapping processes in the charge‐carrier relaxation. The two fast trapping processes are dominated by intrinsic self‐trapping (ca. 1–2 ps) arising from giant exciton–phonon coupling and surface‐defect trapping (ca. 50–100 ps). Slow hot‐carrier relaxation is observed at high pump fluence, and the possible mechanisms for the slow hot‐carrier relaxation are also discussed.     

Cover Picture: Reverse‐Selective Microporous Membrane for Gas Separation (Chem. Asian J. 7/2009)

Reverse‐selective membranes , through which bigger molecules selectively permeate, are attractive for developing chemical processes utilizing hydrogen because they can maintain the high partial pressure of hydrogen required for further downstream utilization. Although several of these chemical processes are operated above 473 K, membranes with outstanding reverse‐selective separation performance at these temperatures are still to be reported. M. Matsukata et al. propose a new adsorption‐based reverse‐selective membrane that utilizes a Na cation occluded in a zeolitic framework. The membrane developed in this work enables selective permeation and separation of bigger polar molecules, such as methanol and water, from hydrogen above 473 K. For more information, see their Full Paper on page 1070 ff.