Compositional variation in hybrid organic-inorganic lead halide perovskites : kinetically- versus thermodynamically-controlled synthesis

Authors thank the Chinese Scholarship Council and the University of St Andrews for Ph.D. Studentship support (to JT, CSC No. 201603780020).The formation and study of partial solid solutions in Az1-xFAxPbBr3, using reportedly similar sized cations azetidinium (Az+) and formamidinium (FA+), was explored via mechanosynthesis and precipitation synthesis. The composition and lattice parameters of samples from both syntheses were analyzed by 1H NMR and Rietveld refinement of powder X-ray diffraction. A clear mismatch in the composition of the perovskite was found between the precipitated samples and the corresponding solutions. Such a mismatch was not observed for samples obtained via mechanosynthesis. The discrepancy suggests products are kinetically-controlled during precipitation, compared to thermodynamically controlled mechanosynthesis. Furthermore, the cell volume as a function of composition in both hexagonal, 6H (Az-rich) and cubic, 3C (FA-rich) perovskite solid solutions suggests that FA+ is actually smaller than Az+, contradicting the literature. In the 3C (Az-poor) solid solutions, the extent of Az1-xFAxPbBr3 is unexpectedly smaller than in the corresponding methylammonium (MA+) system, Az1-xMAxPbBr3, which suggests that the extent of solid solution formation in these halide perovskites is predominantly dependent on the average A-cation size while the size mismatch plays a lesser role in comparison to oxides.PostprintPeer reviewe

Perovskite heterojunction based on CH3NH3PbBr3 single crystal for high-sensitive self-powered photodetector

Perovskite single crystals exhibit extraordinary optoelectronic performances due to their advantages such as low trap-state densities, long carrier diffusion, and large absorption coefficient, and thus, photodetectors based on perovskite single crystals have attracted much research interest. Unlike the reported one-component single-crystal perovskite photodetectors, here, we have developed a facile two-step approach to fabricate a core-shell heterojunction based on the CH3NH3PbBr3 single crystal. A photodetector made of the as-prepared perovskite heterojunction renders the feature of self-power attributed to a built-in electric field in the junction and exhibits a wavelength-dependent responsivity with a peak responsivity up to 11.5 mA W−1 under 450 nm irradiation at zero bias, which is one order of magnitude higher than the CH3NH3PbBr3 single crystal and shows a maximum external quantum efficiency of 3.17%, also higher than the reported 0.2% of the CH3NH3PbBr3 single crystal. Our work may lead to more efficient self-powered heterojunction systems based on perovskite single crystals.Publisher PDFPeer reviewe

Stable 6H organic-inorganic hybrid lead perovskite and competitive formation of 6H and 3C perovskite structure with mixed A cations

We thank the Chinese Scholarship Council for Ph.D. Studentship support (to JT). Computational resources have been provided by the Consortium des Équipements de Calcul Intensif (CÉCI), funded by the Fonds de la Recherche Scientifique de Belgique (F.R.S.-FNRS) under grant no. 2.5020.11. D.B. is an FNRS Research Director.We report the synthesis and properties of a new organic–inorganic hybrid lead perovskite (OIHP), azetidinium lead bromide (AzPbBr3), possessing the 6H perovskite structure (space group P63/mmc with a = 8.745 Å and c = 21.329 Å). This compound has a band gap of 2.81 eV and remains stable for >6 months in the ambient environment. DFT simulations are in fairly good agreement with experiments and indicate that AzPbBr3 is a direct band gap semiconductor. A partial solid solution with the cubic (3C) perovskite methylammonium lead bromide (Az1–xMAxPbBr3) is possible. In Az-rich 6H compositions the lattice volume and band gap are invariant with x (≤0.3), whereas in the MA-rich 3C phase (0.8 ≤ x ≤ 1.0) the lattice parameters and band gap increase with increasing Az content. Although the relatively large band gap of AzPbBr3 makes it unsuitable for photovoltaic applications, the results indicate Az+ is a suitable alternative organic A cation for band gap tuning of OHIPs.PostprintPeer reviewe

A CRISPR/Cas12a-assisted rapid detection platform by biosensing the apxIVA of Actinobacillus pleuropneumoniae

Actinobacillus pleuropneumoniae is an important respiratory pig pathogen that causes substantial losses in the worldwide swine industry. Chronic or subclinical infection with no apparent clinical symptoms poses a challenge for preventing transmission between herds. Rapid diagnostics is important for the control of epidemic diseases. In this study, we formulated an A. pleuropneumoniae species-specific apxIVA-based CRISPR/Cas12a-assisted rapid detection platform (Card) that combines recombinase polymerase amplification (RPA) of target DNA and subsequent Cas12a ssDNase activation. Card has a detection limit of 10 CFUs of A. pleuropneumoniae, and there is no cross-reactivity with other common swine pathogens. The detection process can be completed in 1 h, and there was 100% agreement between the conventional apxIVA-based PCR and Card in detecting A. pleuropneumoniae in lung samples. Microplate fluorescence readout enables high-throughput use in diagnostic laboratories, and naked eye and lateral flow test readouts enable use at the point of care. We conclude that Card is a versatile, rapid, accurate molecular diagnostic platform suitable for use in both laboratory and low-resource settings

miR-100 Reverses Cisplatin Resistance in Breast Cancer by Suppressing HAX-1

Background/Aims: Breast cancer (BC) is the most common cancer in women worldwide. Despite great advancements in cancer therapy in recent years, surgery and chemotherapy are still the mainstays of BC treatment. However, cancer cells usually develop mechanisms to evade cell death induced by chemotherapy. Thus, strategies are needed to reverse the chemoresistance of cancer cells. Methods: We established cisplatin-resistant BC models in MDA-MB-231 and MCF-7 BC cell lines through long-term exposure to cisplatin. Quantitative reverse transcription PCR was used to examine the expression of microRNA (miR)-100. MTT cell viability assays were performed to determine cell viability. Regulation of hematopoietic cell-specific protein 1-associated protein X-l (HAX-1) targeted by miR-100 was confirmed by western blotting and luciferase reporter assays. The mitochondrial membrane potential and apoptosis were measured by flow cytometry. Release of cytochrome c from the mitochondria into the cytoplasm, HAX-1 expression, and activation of caspase-9 and caspase-3 were detected by western blotting. Results: A clear decrease in miR-100 expression was observed in cisplatin-resistant MDA-MB-231 and MCF-7 cells (MDA-MB-231/R and MCF-7/R). Overexpression of miR-100 increased the sensitivity of MDA-MB-231/R and MCF-7/R cells to cisplatin treatment and promoted cisplatin-induced mitochondrial apoptosis by targeting HAX-1 gene. Conclusions: MiR-100 targeted HAX-1 to increase the chemosensitivity of BC by mediating the mitochondrial apoptosis pathway

Protective Effect of Tetrahydroxystilbene Glucoside on 6-OHDA-Induced Apoptosis in PC12 Cells through the ROS-NO Pathway

Oxidative stress plays an important role in the pathogenesis of neurodegenerative diseases, such as Parkinson's disease. The molecule, 2,3,5,4′-tetrahydr- oxystilbene-2-O-β-D-glucoside (TSG), is a potent antioxidant derived from the Chinese herb, Polygonum multiflorum Thunb. In this study, we investigated the protective effect of TSG against 6-hydroxydopamine-induced apoptosis in rat adrenal pheochromocytoma PC12 cells and the possible mechanisms. Our data demonstrated that TSG significantly reversed the 6-hydroxydopamine-induced decrease in cell viability, prevented 6-hydroxydopamine-induced changes in condensed nuclei and decreased the percentage of apoptotic cells in a dose-dependent manner. In addition, TSG slowed the accumulation of intracellular reactive oxygen species and nitric oxide, counteracted the overexpression of inducible nitric oxide syntheses as well as neuronal nitric oxide syntheses, and also reduced the level of protein-bound 3-nitrotyrosine. These results demonstrate that the protective effects of TSG on rat adrenal pheochromocytoma PC12 cells are mediated, at least in part, by the ROS-NO pathway. Our results indicate that TSG may be effective in providing protection against neurodegenerative diseases associated with oxidative stress

Azetidinium Lead Halide Ruddlesden–Popper Phases

A family of Ruddlesden–Popper (n = 1) layered perovskite-related phases, Az2PbClxBr4−x with composition 0 ≤ x ≤ 4 were obtained using mechanosynthesis. These compounds are isostructural with K2NiF4 and therefore adopt the idealised n = 1 Ruddlesden–Popper structure. A linear variation in unit cell volume as a function of anion average radius is observed. A tunable bandgap is achieved, ranging from 2.81 to 3.43 eV, and the bandgap varies in a second-order polynomial relationship with the halide composition

Exploring azetidinium as the A-site in organic-inorganic hybrid perovskites

Organic inorganic hybrid perovskites (OIHPs) have appealing optoelectronic properties. As sample preparation is relatively straightforward, there are opportunities to investigate novel compositions and structures. This thesis concerns the synthesis, structure and optoelectrical properties of OIHPs with azetidinium as an A-site cation. Azetidinium [(CH₂)₃NH₂⁺, Az] is a four-member ring ammonium, and its size is calculated to be promising as an A-cation for OIHPs. A stable 6H hexagonal perovskite AzPbBr₃ was synthesised and analysed, and its bandgap was determined to be 2.81 eV. On cooling, AzPbBr₃ undergoes a symmetry lowering distortion which was identified by variable temperature PXRD and dielectric spectroscopy. An anisotropic change in lattice parameters on cooling marked a phase transition likely driven by the Pb⋯Pb repulsion in the face sharing octahedra. Compositional and structural analyses were performed on precipitation synthesised and mechanosynthesised OIHPs Az₁₋ₓFAₓPbBr₃ and Az₁₋ₓMAₓPbBr₃ (0 ≤ x ≤ 1). For samples obtained from precipitation synthesis, the actual FA% or MA% in the precipitate was found to be less than the nominal composition in the reaction solution. No such mismatch was found for mechanosynthesised samples. PXRD indicated partial solid solution formation for Az-rich and MA- or FA-rich compositions, separated by an intermediate two-phase region. The result suggests the extent of the solid solution of halide perovskites is dependent only on the average A-cation size; the size mismatch is less of an influence. This is in contrast to solid solution formation observed in oxide perovskites. A tuneable bandgap was achieved ranging from 2.00 eV (AzPbI₃) to 3.41 eV (AzPbCl₃) for the mixed halide perovskite AzPbBr₃₋ₓXₓ (X = Cl or I, 0 ≤ x ≤ 3). The structural analyses revealed a complete 6H solid solution for AzPbBr₃₋ₓClₓ in comparison to the structural progression from 6H, 4H to 9R polytypes, when varying the halide composition from Br (x = 0) to I (x = 3) in AzPbBr₃₋ₓIₓ. A linear variation in unit cell volume as a function of anion average radius was observed not only within the solid solution of each polytype (following Vegard’s law) but continuously across all three polytypes. Preliminary results on the synthesis and structural analysis indicate that Az₂PbBr₄ adopts the = 1 Ruddlesden-Popper structure while azetidinium bismuth bromide has a 1D chain structure. Detailed structural and optical analysis are planned in future projects."My PhD Studentship was supported by the Chinese Scholarship Council and the University of St Andrews (CSC No. 201603780020)." -- Fundin

Size Isn’t Everything - Compositional Variation in Hybrid Organic-Inorganic Lead Halide Perovskites: Kinetically- versus Thermodynamically-controlled Synthesis

The formation and study of a partial solid solution Az1-xFAxPbBr3, using ‘similar’ sized cations azetidinium (Az+) and formamidinium (FA+), was explored via mechanosynthesis and precipitation synthesis. The composition and lattice parameters of samples from both syntheses were analysed by 1H NMR and Rietveld refinement of the powder X-ray diffraction. A clear mismatch in the composition of the perovskite was found between the precipitated samples and the corresponding solutions. Such a mismatch was not observed for samples obtained via mechanosynthesis. The discrepancy suggests products are kinetically-controlled during precipitation, compared to thermodynamically-controlled mechanosynthesis. Furthermore, the cell volume as a function of composition in both 6H (Az-rich) and 3C (FA-rich) solid solutions suggests that FA+ is actually smaller than Az+, contradicting the literature. In the 3C (Az-poor) solid solutions, the extent of Az1-xFAxPbBr3 is unexpectedly smaller than Az1-xMAxPbBr3, again in contradiction to the expectation based on the reported cation sizes. These results indicate that other factors, as yet unidentified, must also contribute to the solid solution formation of organic-inorganic hybrid perovskites, not simply the relative sizes of the A-site cations.</p