Photoprotection in metal halide perovskites by ionic defect formation

Photostability is critical for long-term solar cell operation. While light-triggered defects are usually reported as evidence of material degradation, we reveal that the formation of certain defects in metal halide perovskites is crucial for protection against intense or prolonged light exposure. We identify an inherent self-regulating cycle of formation and recovery of ionic defects under light exposure that mitigates the overheating of the lattice due to hot carrier cooling, which allows exposure to several thousand suns without degrading. The excess energy instead dissipates by forming defects, which in turn alters the optoelectronic properties of the absorber, resulting in a temporary reduction of photon absorption. Defects gradually recover to restore the original optoelectronic properties of the absorber. Photoprotection is a key feature for the photostability in plants. Thus, finding a protection mechanism in metal halide perovskites similar to those in nature is encouraging for the development of long-term sustainable solar cells

Promising Perspectives on the Use of Fullerenes as Efficient Containers for Beryllium Atoms

The possibility of using fullerenes as containers for toxic beryllium atoms is studied by a multi-scale approach in which first-principles and classical molecular dynamics simulations are combined. By studying the energetics, electronic and spectroscopic properties of Be-fullerene systems and by simulating their interaction at finite temperature in vacuo and in representative biological environments it is concluded that: i) Be endohedral complexes can be obtained by implanting Be atoms at energies >2.3 eV that is consistent with laser implantation technologies; ii) it is in principle possible to distinguish stable endohedral complexes from metastable exohedral ones by optical absorption, suggesting that optical spectroscopy can be a valuable a non-destructive technique to assist the synthesis and the control of implanted films iii) the Be-endohedral complexes are long-lived and thermodynamically stable and can confine beryllium both in vacuo and in aqueous solution; iv) Be@C60 complexes are likely unable to penetrate the selectivity filters of a prototypical protein showing that fullerene prevents undesired interactions with biomolecules and toxicity effects of Be2+ related to replacement of the Ca2+. Overall, these results provide an assessment on the possibility to encapsulate Be atoms into fullerenes by ion implantation to synthesize inert and highly stable and safe molecular containers for toxic beryllium radionuclides. Great opportunities are expected for the realization and application of Be-C60 complexes to nanotechnology and nanomedicine with particularly appealing perspectives in the field of neutron capture therapy of cancer

Dynamic Local Structure in Caesium Lead Iodide: Spatial Correlation and Transient Domains

Metal halide perovskites are multifunctional semiconductors with tunable structures and properties. They are highly dynamic crystals with complex octahedral tilting patterns and strongly anharmonic atomic behaviour. In the higher temperature, higher symmetry phases of these materials, several complex structural features have been observed. The local structure can differ greatly from the average structure and there is evidence that dynamic two-dimensional structures of correlated octahedral motion form. An understanding of the underlying complex atomistic dynamics is, however, still lacking. In this work, the local structure of the inorganic perovskite CsPbI$_3$ is investigated using a new machine learning force field based on the atomic cluster expansion framework. Through analysis of the temporal and spatial correlation observed during large-scale simulations, we reveal that the low frequency motion of octahedral tilts implies a double-well effective potential landscape, even well into the cubic phase. Moreover, dynamic local regions of lower symmetry are present within both higher symmetry phases. These regions are planar and we report the length and timescales of the motion. Finally, we investigate and visualise the spatial arrangement of these features and their interactions, providing a comprehensive picture of local structure in the higher symmetry phases

Dynamic Local Structure in Caesium Lead Iodide: Spatial Correlation and Transient Domains

Metal halide perovskites are multifunctional semiconductors with tunable structures and properties. They are highly dynamic crystals with complex octahedral tilting patterns and strongly anharmonic atomic behavior. In the higher temperature, higher symmetry phases of these materials, several complex structural features are observed. The local structure can differ greatly from the average structure and there is evidence that dynamic 2D structures of correlated octahedral motion form. An understanding of the underlying complex atomistic dynamics is, however, still lacking. In this work, the local structure of the inorganic perovskite CsPbI3 is investigated using a new machine learning force field based on the atomic cluster expansion framework. Through analysis of the temporal and spatial correlation observed during large-scale simulations, it is revealed that the low frequency motion of octahedral tilts implies a double-well effective potential landscape, even well into the cubic phase. Moreover, dynamic local regions of lower symmetry are present within both higher symmetry phases. These regions are planar and the length and timescales of the motion are reported. Finally, the spatial arrangement of these features and their interactions are investigated and visualized, providing a comprehensive picture of local structure in the higher symmetry phases

Radiomic Features from Post-Operative 18F-FDG PET/CT and CT Imaging Associated with Locally Recurrent Rectal Cancer: Preliminary Findings

Locally Recurrent Rectal Cancer (LRRC) remains a major clinical concern, it rapidly invades pelvic organs and nerve roots, causing severe symptoms. Curative-intent salvage therapy offers the only potential for cure but it has a higher chance of success when LRRC is diagnosed at an early stage. Imaging diagnosis of LRRC is very challenging due to fibrosis and inflammatory pelvic tissue which can mislead even the most expert reader. This study exploited a radiomic analysis to enrich, through quantitative features, the characterization of tissue properties, thus favouring an accurate detection of LRRC by Computed Tomography (CT) and 18F-FDG-Positron Emission Tomography/CT (PET/CT). Of 563 eligible patients, undergoing radical resection (R0) of primary RC, 57 patients with suspected LRRC were included, 33 of which histologically confirmed. After manually segmenting suspected LRRC in CT and PET/CT, 144 radiomic features (RFs) were generated, and RFs were investigated for univariate significant discriminations (Wilcoxon rank-sum test, p<0.050) of LRRC from NO LRRC. Five RFs in PET/CT (p<0.017) and 2 in CT (p<0.022) enabled, individually, a clear distinction of the groups, and one RF was shared by PET/CT and CT. Besides confirming the potential role of radiomics to advance LRRC diagnosis, the aforementioned shared RF describes LRRC as tissues having high local inhomogeneity due to evolving tissue’s properties

Ag/In lead‐free double perovskites

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