29 research outputs found
Chirality-induced spin selectivity and chiroptical properties in layered halide perovskites
No full textInternational audience3-dimensional (3D) halide perovskites AMX3 (A: organic cation, M: metal ion, X: halide) have shown spectacular results in optoelectronic devices. However, they offer limited choice of metals and organic cations, which limits the chemical design of optimal materials. This is not the case of lower dimensional materials, e.g. layered (2D) halide perovskites (LHPs) [1], that impose far less constraints over the organic spacer. It then become possible to associate the exceptional optoelectronic properties of halide perovskites with chiral cations to reach promising materials for chiroptical and magnetochiral applications [2].Here, we report joint experimental and theoretical investigations of LHPs with exceptional (i) chiroptical, and (ii) magnetochiral properties. Firstly, the enantiopure 3BrMBA2PbI4 (MBA = methylbenzylammonium) perovskite thin films exhibit external photoluminescence quantum efficiency as high as 39% and circularly polarized photoluminescence up to 52%, at room temperature [3]. Next, we consider a series of chiral lead-bromide networks which crystallize in enantiomorphic polar space groups P41212 and P43212 for the R and S enantiomers, respectively [4]. Chirality-induced spin selectivity (CISS) effect measurements performed over those materials by magnetic conducting-probe atomic force microscopy (mc-AFM) reveal a spin polarization of about 40% [4].We use a set of experimental characterizations (e.g. single-crystal x-ray diffraction), and theoretical tools (semi-empirical modeling and density-functional theory based calculations) to describe the chiral-related properties of these LHPs and help the cation engineering of efficient chiral halide perovskites.Acknowledgment. The work was performed with funding from Agence Nationale pour la Recherche under grant ANR-18-CE05-0026 (MORELESS project), the European Union’s Horizon 2020 program, through an innovation action under grant agreement no. 861985 (PeroCUBE) and a FET Open research and innovation action under the grant agreement no. 899141 (PoLLoC). This work was granted access to the HPC resources of TGCC under the allocations 2022-A0130907682 made by GENCI.[1]B. Saparov, D. B. Mitzi, Chem. Rev. 2016, 116, 4558; L. Pedesseau, M.K. et al., ACS Nano 2016, 10, 9776; C. Katan, N. Mercier, J. Even, Chem. Rev. 2019, 119, 3140.[2]Y.-H. Kim et al., Science 2021, 371, 1129 ; M. K. Jana et al., Nat. Commun. 2021, 12, 4982 ; G. Long et al., Nat. Rev. Mater. 2020, 5, 423 ; H. Lu, Z. V. Vardeny, M. C. Beard, Nat. Rev. Chem. 2022, 6, 470.[3]S. Liu, M.K. et al., submitted manuscript.[4]A. Abhervé, M.K. et al., submitted manuscript
Photoluminescence and spin selectivity in chiral layered halide perovskites
No full textInternational audienceIf 3-dimensional (3D) halide perovskites AMX3 (A: organic cation, M: metal ion, X: halide) have shown spectacular results in optoelectronic devices, they offer limited choice of metals and organic cations. This is not the case of the other shapes that impose far less constraints over the chemical design of the organic spacer, such as layered (2D) halide perovskites (LHPs) [1]. The optical properties of those materials are marked by strong excitonic features that can be tuned by materials engineering over the chemical nature of the metals [2] or the organic spacer [3]. Excitonic properties can also be modified by controlling the structural properties of LHPs guided by the concept of lattice mismatch recently proposed [4]. Finally, the optical properties of LHPs can be enriched by substituting the optically-inert organic spacer by a chiral cation, leading to high responses for circularly polarized absorption and emission, but also spin selectivity through the materials [5]. Here, we will show how modeling and computational investigations can contribute to the writing of guidelines for the design of optimized LHPs for optoelectronic and spintronic applications.Acknowledgment. The work at ISCR and Institut FOTON was performed with funding from the European Union’s Horizon 2020 program, through an innovation action under grant agreement no. 861985 (PeroCUBE) and through a FET Open research and innovation action under the grant agreement no. 899141 (PoLLoC). This work was granted access to the HPC resources of TGCC under the allocations 2022-A0130907682 made by GENCI.[1]B. Saparov, D. B. Mitzi, Chem. Rev. 2016, 116, 4558; L. Pedesseau, M.K. et al., ACS Nano 2016, 10, 9776; C. Katan, N. Mercier, J. Even, Chem. Rev. 2019, 119, 3140.[2]P. Fu, M.K. et al., J. Am. Chem. Soc. 2023, in press.[3]E. S. Vasileiadou, M.K. et al., J. Am. Chem. Soc. 2022, 144, 6390.[4]M. Kepenekian et al., Nano Lett. 2018, 18, 5603; E. S. Vasileiadou, M.K. et al., Chem. Mater. 2021, 33, 5085.[5]S. Liu, M.K. et al., submitted manuscript; A. Abhervé, M.K. et al., submitted manuscript
Pulsed laser/ electrodeposited CuBi2O4/BiVO4 p-n heterojunction for solar water splitting
No full textLight-induced optical orientation of magnetic moments in transition-metal doped hybrid metal halide perovskites
No full textUsing optical orientation to manipulate magnetic moments in matter with light is a key objective in opto-spintronics, however, realizations of such control on ultrafast timescales are limited. Here, we report ultrafast optical control of magnetic moment orientation in magnetically doped metal halide perovskites. Employing intense pulses of circularly polarized light, we inject populations of spin-polarized charge carriers in pristine and manganese-doped MAPbBr3 thin films. Using transient Faraday rotation spectroscopy, we probe the ultrafast magnetic moment dynamics following photoexcitation and find that light-induced magnetization in doped samples is increased by a factor of 10. We attribute this to photoexcited carriers acting on the magnetic moments of manganese dopant-ions via the sp-d exchange interaction, which forces them to align on picosecond timescales. Our findings open new avenues for device structures that use hybrid metal halide perovskites for ultrafast optical manipulation and read-out of magnetic order with the potential for high switching rates
Comparative analysis of six nutritional scores in predicting prognosis of COVID-19 patients
No full textBackgroundIdentifying nutritional risk in COVID-19 patients poses a challenge due to the unique qualities of every nutritional screening instrument. The objective was to assess the efficacy of six nutritional scores, including the Nutritional Risk Screening 2002 (NRS-2002) score, the NUTRIC (nutrition risk in the critically ill) score, the modified NUTRIC score, the prognostic nutritional index (PNI), controlling nutritional status (CONUT) score, TCB index (TCBI), predicting prognosis of COVID-19 patients.MethodsClinical data were collected from COVID-19 patients admitted to the First Affiliated Hospital of Wenzhou Medical University between December 2022 and February 2023. Participants in this research were divided into two groups: all patients and those specifically from the intensive care unit (ICU). Each group was further stratified into two groups: survivors and non-survivors.Result506 COVID-19 patients and 190 COVID-19 patients in intensive care unit (ICU) were evaluated. In all COVID-19 patients, we found that NRS-2002 (p < 0.001) and TCBI (p = 0.002) were statistically significant independent predictors in multivariate analyses, while APACHE II score (p = 0,048) and the mNUTRIC score (p = 0.025) were statistically significant independent predictors in multivariate analyses in ICU patients. The NRS-2002 demonstrated a higher AUC value (0.687) than other nutritional scores in all patients, with an optimum cut-off value of 3, translating into a corresponding sensitivity of 66.2% and specificity of 68.7%. With an optimum cut-off value of 4, the mNUTRIC score demonstrated a higher AUC value (0.884) in ICU patients, resulting in a sensitivity of 88.4% and a specificity of 76.9%. By using the discrimination and clinical application (DCA) curve, NRS-2002 demonstrated the greatest net benefit in all patients, while NUTRIC score and mNUTRIC score offered the more significant overall advantage than other nutritional scores in ICU patients. Kaplan–Meier analyses showed lower survival rates in patients in low nutritional risk.ConclusionMalnutrition was common in COVID-19 patients. The mNUTRIC score and NRS-2002 were, respectively, more effctive scoring systems of prognosis in all COVID-19 patients and severe or critical COVID-19 patients of the intensive care unit (ICU)
Regulation of the Psoriatic Chemokine CCL20 by E3 Ligases Trim32 and Piasy in Keratinocytes
No full textPsoriasis is an inflammatory skin disorder with aberrant regulation of keratinocytes and immunocytes. Although it is well known that uncontrolled keratinocyte proliferation is largely driven by proinflammatory cytokines from the immunocytes, the functional role of keratinocytes in the regulation of immunocytes is poorly understood. Recently, we found that tripartite motif-containing protein 32 (Trim32), an E3-ubiquitin ligase, is elevated in the epidermal lesions of human psoriasis. We previously showed that Trim32 binds to the protein inhibitor of activated STAT-Y (Piasy) and mediates its degradation through ubiquitination. Interestingly, the Piasy gene is localized in the PSORS6 susceptibility locus on chromosome 19p13, and Piasy negatively regulates the activities of several transcription factors, including NF-κB, STAT, and SMADs, that are implicated in the pathogenesis of psoriasis. In this study, we show that Trim32 activates, and Piasy inhibits, keratinocyte production of CC chemokine ligand 20 (CCL20), a psoriatic chemokine essential for recruitment of DCs and T helper (Th)17 cells to the skin. Further, Trim32/Piasy regulation of CCL20 is mediated through Piasy interaction with the RelA/p65 subunit of NF-κB. As CCL20 is activated by Th17 cytokines, the upregulation of CCL20 production by Trim32 provides a positive feedback loop of CCL20 and Th17 activation in the self-perpetuating cycle of psoriasis
Electrically‐Switchable Gain in Optically Pumped CsPbBr Lasers With Low Threshold at Nanosecond Pumping
No full textMetal halide perovskites hold promise for nonepitaxial laser diodes, yet, continuous-wave (CW) optically pumped (photonic) lasing in CsPbBr remains elusive despite its superior thermal- and photo-stability among the perovskite family. This work reports on CsPbBr vertical cavity surface emitting lasers with low lasing thresholds (1.3 µJ cm) at nanosecond pumping and remarkable lasing stability. Furthermore, the electrically switchable gain is achieved in CsPbBr electrically assisted optically pumped laser (EAOPL) devices by leveraging ion migration. Applying a small positive DC voltage to the EAOPL device significantly reduces the lasing threshold under nanosecond laser excitation and enhances the cavity mode intensity at CW laser excitation. These findings present a novel strategy, combining a small DC voltage with an electrical pulse, for exploring electrical injection lasing in CsPbBr3 perovskites
Morphological Insights into the Degradation of Perovskite Solar Cells under Light and Humidity
No full textPerovskite solar cells (PSCs) have achieved competitive
power conversion
efficiencies compared with established solar cell technologies. However,
their operational stability under different external stimuli is limited,
and the underlying mechanisms are not fully understood. In particular,
an understanding of degradation mechanisms from a morphology perspective
during device operation is missing. Herein, we investigate the operational
stability of PSCs with CsI bulk modification and a CsI-modified buried
interface under AM 1.5G illumination and 75 ± 5% relative humidity,
respectively, and concomitantly probe the morphology evolution with
grazing-incidence
small-angle X-ray scattering. We find that volume expansion within
perovskite grains, induced by water incorporation, initiates the degradation
of PSCs under light and humidity and leads to the degradation of device
performance, in particular, the fill factor and short-circuit current.
However, PSCs with modified buried interface degrade faster, which
is ascribed to grain fragmentation and increased grain boundaries.
In addition, we reveal a slight lattice expansion and PL redshifts
in both PSCs after exposure to light and humidity. Our detailed insights
from a buried microstructure perspective on the degradation mechanisms
under light and humidity are essential for extending the operational
stability of PSCs
Ligand-Induced Crystallization Control in MAPbBr3 Hybrid Perovskites for High Quality Nanostructured Films [Research Data]
No full textControlling the formation of hybrid perovskite thin films is crucial in obtaining high-performance optoelectronic devices, since factors like morphology and film thickness have a profound impact on a film’s functionality. For light-emitting applications grain sizes in the sub-micrometer-range have previously shown enhanced brightness. It is therefore crucial to develop simple, yet reliable methods to produce such films. Here, a solution-based synthesis protocol for the on-substrate formation of MAPbBr3 (MA = methylammonium) nanostructures by adding the bifunctional rac-3-aminobutyric acid to the precursor solution is reported. This synthesis route improves key optical properties such as photoluminescence quantum yields and life times of excited states by inducing a controlled slow-down of the film formation and suppressing agglomeration effects. In-situ spectroscopy reveals a delayed and slowed down crystallization process, which achieves synthesis of perovskite structures with much reduced defect densities. Further, aggregation can be controlled by the amount of amino acid added and adjusting the synthesis protocol allows to produce cubic crystallites with targeted size from nanometer to micrometer scales. The nanocrystalline MAPbBr3 samples show enhanced amplified spontaneous emission (ASE) intensities, reduced ASE thresholds and purer ASE signals, compared to pristine films, even under intense optical driving, making them promising structures for lasing applications
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Ligand‐Induced Crystallization Control in MAPbBr3 Hybrid Perovskites for High Quality Nanostructured Films
No full textAbstract Controlling the formation of hybrid perovskite thin films is crucial in obtaining high‐performance optoelectronic devices, since factors like morphology and film thickness have a profound impact on a film's functionality. For light‐emitting applications grain sizes in the sub‐micrometer‐range have previously shown enhanced brightness. It is therefore crucial to develop simple, yet reliable methods to produce such films. Here, a solution‐based synthesis protocol for the on‐substrate formation of MAPbBr 3 (MA = methylammonium) nanostructures by adding the bifunctional rac ‐3‐aminobutyric acid to the precursor solution is reported. This synthesis route improves key optical properties such as photoluminescence quantum yields and life times of excited states by inducing a controlled slow‐down of the film formation and suppressing agglomeration effects. In situ spectroscopy reveals a delayed and slowed down crystallization process, which achieves synthesis of perovskite structures with much reduced defect densities. Further, aggregation can be controlled by the amount of amino acid added and adjusting the synthesis protocol allows to produce cubic crystallites with targeted size from nanometer to micrometer scales. The nanocrystalline MAPbBr 3 samples show enhanced amplified spontaneous emission (ASE) intensities, reduced ASE thresholds and purer ASE signals, compared to pristine films, even under intense optical driving, making them promising structures for lasing applications
