Shiling Dong

Abstract:

Lead-free perovskite-inspired materials have emerged as promising candidates for direct X-ray detection. However, in the early exploration of emerging materials, the focus was on large single crystals. Herein, we report a facile, scalable, single-step synthesis of high-quality Cs3Bi2I9 nanocrystals (NCs) directly from their precursor powders through an ultrasonication approach. The large-scale synthesis of the NCs allowed for the production of 0.78 cm2 pellets used in the fabrication of X-ray detection devices, which exhibit a high bulk resistivity of 1 × 1011 Ω cm and a low dark current density of 3.3 nA cm–2 under an applied bias of 50 V (357 V cm–1 electric field). These devices achieve a limit detection of 108 nGyair s–1, an order of magnitude improvement over the a-Se used in commercial medical imaging, along with stable current under continuous X-ray exposure with a peak energy of 35 keVp. Finally, we demonstrate the scale-up of these detectors by producing thick films 9 cm2 in area, achieving a performance comparable to that of the detectors based on pellets.

Abstract:

Efforts to develop lead-free and stable alternatives to halide perovskites have thus far mostly yielded materials with power conversion efficiencies (PCEs) well below 10% in solar cells. Recently, photovoltaics based on CsBiSCl2 were reported to achieve 10.38% PCE. Still, the crystal structure is unknown, and it is unclear whether the reported thin film synthesis method could realize thin films with the desired phase and stoichiometry. Herein, we use ab initio Random Structure Searching (AiRSS) with a bespoke machine learned interatomic potential to explore the potential energy surface of CsBiSCl2, finding the previously-proposed cubic perovskite structure to be implausible. The lowest-energy structure we find is a four formula unit orthorhombic structure (Pnma space group) that lies 2.4 meV per atom above the convex hull. There is strong competition in the Cs–Bi–S–Cl family, which can lead to phase impurities. By examining the reported solution synthesis method, we find that it is challenging to obtain the dimethylammonium bismuth sulfide intermediate product, and that Bi2S3 with dimethylammonium iodide on the surface likely forms instead. The significant I-containing residues in this intermediate results in Cs3Bi2I9 being preferentially formed in thin films instead of CsBiSCl2. Solid state synthesis without I present leads to phase impurities, consistent with the lowest-energy CsBiSCl2 phase being metastable. Taking these experimental and computational results together, it is unlikely that >10%-efficient CsBiSCl2 solar cells have been achieved.

Abstract:

Raw data for all the figures in the main text and SI for this paper

Abstract:

Raw data for all the figures in the main text and SI for this paper

Abstract:

Electrospinning has been applied to produce ceramic fibers using sol gel-based spinning solutions consisting of ceramic precursors, a solvent, and a polymer to control the viscosity of the solution. However, the addition of polymers to the spinning solution makes the process more complex, increases the processing time, and results in porous mechanically weak ceramic fibers. Herein, we develop a coelectrospinning technique, where a nonspinnable sol (<10 mPa s) consisting of only the ceramic precursor(s) and solvent(s) is encapsulated inside a polymeric shell, forming core-shell precursor fibers that are further calcined into ceramic fibers with reduced porosity, decreased surface defects, uniform crystal packing, and controlled diameters. We demonstrate the versatility of this method by applying it to a series of nonspinnable sols and creating high-quality ceramic fibers containing TiO₂, ZrO₂, SiO₂, and Al₂O₃. The polycrystalline TiO₂ fibers possess excellent flexibility and a high Young's modulus reaching 54.3 MPa, solving the extreme brittleness problem of the previously reported TiO₂ fibers. The single-component ZrO₂ fibers exhibit a Young's modulus and toughness of 130.5 MPa and 11.9 KJ/m³, respectively, significantly superior to the counterparts prepared by conventional sol-gel electrospinning. We also report the creation of ceramic fibers in micro- and nanospring morphologies and examine the formation mechanisms using thermomechanical simulations. The fiber assemblies constructed by the helical fibers exhibit a density-normalized toughness of 3.5-5 times that of the straight fibers due to improved fracture strain. This work expands the selection of the electrospinning solution and enables the development of ceramic fibers with more attractive properties.