Structural and vibrational properties of Sb2S3: Practical methodologies for accelerated research and application of this low dimensional material.

Recently, the interest for the family of low dimensional materials has increased significantly due to the anisotropic nature of their fundamental properties. Among them, antimony sulfide (Sb2S3) is considered a suitable material for various solid-state devices. Although the main advantages and physicochemical properties of Sb2S3 are known, some doubtful information remains in literature and methodologies to easily assess its critical properties are missing. In this study, an advanced characterization of several types of Sb2S3 samples, involving the Rietveld refinement of structural properties, and Raman spectroscopy analysis, completed with lattice dynamics investigations reveal important insights into the structural and vibrational characteristics of the material. Based on the gathered data, fast, non-destructive, and non-invasive methodologies for assessment of the crystallographic orientation and point defect concentration of Sb2S3 are proposed. With a high resolution in-sample and in-situ assessment, these methodologies will serve for accelerating the research and application of Sb2S3 in the research field.

Accelerating the Development of Thin Film Photovoltaic Technologies: An Artificial Intelligence Assisted Methodology Using Spectroscopic and Optoelectronic Techniques.

Thin film photovoltaic (TFPV) materials and devices present a high complexity with multiscale, multilayer, and multielement structures and with complex fabrication procedures. To deal with this complexity, the evaluation of their physicochemical properties is critical for generating a model that proposes strategies for their development and optimization. However, this process is time-consuming and requires high expertise. In this context, the adoption of combinatorial analysis (CA) and artificial intelligence (AI) strategies represents a powerful asset for accelerating the development of these complex materials and devices. This work introduces a methodology to facilitate the adoption of AI and CA for the development of TFPV technologies. The methodology covers all the necessary steps from the synthesis of samples for CA to data acquisition, AI-assisted data analysis, and the extraction of relevant information for research acceleration. Each step provides details on the necessary concepts, requirements, and procedures and are illustrated with examples from the literature. Then, the application of the methodology to a complex set of samples from a TFPV production line highlights its ability to rapidly glean significant insights even in intricate scenarios. The proposed methodology can be applied to other types of materials and devices beyond PV and using different characterization techniques.

Overcoming Limitations in Water-Ethanol Sprayed Superstrate Solar Cells by Compositional Engineering of Cu2CdSn(S,Se)4.

The increasing demand for solar energy requires materials from earth-abundant elements to ensure cost-effective production. One such light harvester Cu2CdSn(S,Se)4 fulfills this property. We report the development of functional solar cells based on Cu2CdSn(S,Se)4, which has been previously unreported. Furthermore, we deposited the thin films of Cu2CdSn(S,Se)4 by spray pyrolysis using environmentally benign solvents, in a superstrate architecture, reducing the potential cost of upscaling, the environmental hazards, and enabling its use in semitransparent or tandem solar cells. We analyze the Cu2CdSn(S,Se)4 and its optoelectronic characteristics with different sulfur and selenium ratios in the composition. We noted that Se is homogeneously distributed in the absorber and electron transport layer, forming a Cd(S,Se) phase that impacts the optoelectronic properties. The introduction of Se, up to 30%, is found to have a positive impact on the solar cell performance, largely improving the fill factor and absorption in the infrared region, while the voltage deficit is reduced. The device with a Cu2CdSn(S2.8Se1.2) composition had a 3.5% solar-to-electric conversion efficiency, which is on par with the reported values for chalcogenides and the first report using Cu2CdSn(S,Se)4. We identified the critical factors that limit the efficiency, revealing pathways to further reduce the losses and improve the performance. This work provides the first proof of concept of a novel material, paving the way for developing cost-efficient solar cells based on earth-abundant materials.

Coinfecciones y sobreinfecciones en pacientes con diagnóstico de COVID-19 ingresados en terapia del Hospital Hermanos Ameijeiras / Behavior of coinfections and superinfections in COVID-19 patients admitted to the intensive care unit at Hermanos Ameijeiras Hospital

Introducción: La enfermedad COVID-19 se ha asociado a un incremento de los ingresos en terapia intensiva. La probabilidad de muerte se eleva con las coinfecciones y sobreinfecciones. Objetivo: Determinar la presencia de coinfecciones y aparición de sobreinfecciones en pacientes con COVID-19 ingresados en terapia, los factores asociados a esta y su relación con la mortalidad. Métodos: Se realizó un estudio analítico transversal donde se estudió a 79 pacientes positivos al virus SARS-CoV-2 en 8 meses en el servicio de la terapia del Hospital Hermanos Ameijeiras. Se estudiaron variables demográficas, clínicas y de manejo en terapia. Las variables categóricas se expresaron en frecuencias absoluta y relativa. Las variables cuantitativas se describieron según la mediana y sus rangos intercuartílicos. Se empleó la prueba de rangos de Wilcoxon, ji al cuadrado de Pearson y el modelo de regresión logística multinomial para determinar las variables predictoras independientes de la sobreinfección. Resultados: Presentaron sobreinfección 34 pacientes (43 %). Hubo una mortalidad del 43 % con 34 pacientes, de estos se sobreinfectaron 18 pacientes. Se obtuvo una asociación causal entre la sobreinfección y la estadía hospitalaria (OR: 1,56; IC: 95 %: 1,26-2,08; p < 0,001), el uso de ventilación mecánica invasiva (OR: 3,28; IC: 95 %: 1,30-8,73; p = 0,014) y el tiempo de empleada esta (OR: 1,37; IC: 95 %: 1,15-1,71; p< 0,001). Conclusiones: No se encontró asociación estadística entre la mortalidad y la sobreinfección en los pacientes estudiados. Hubo poca representación de coinfecciones. La estadía en terapia, el uso de ventilación mecánica invasiva y el tiempo de empleada esta fueron variables predictoras en la aparición de sobreinfección.

Introduction: COVID-19 is associated with an increase in the number of admissions to the intensive care units. The likelihood of fatality cases increases with coinfections and superinfections. Objective: To determine the presence of coinfections and the occurrence of superinfections in COVID-19 patients admitted to the intensive care unit, its associated factors and its relationship with mortality. Methods: It was conducted a cross-sectional analytic study in 79 patients with positive SARS-CoV-2 tests during eight months in the intensive care units at Hermanos Ameijeiras Hospital. Demographic, clinical and management variable were studied. Categorical variables were expressed in terms of absolute and relative frequencies. Quantitative variables were described based on their median and their interquartile ranges. The Wilcoxon rank test, Pearson's chi-squared test and the multinomial logistic regression model were used to determine the independent predictor variables of superinfection. Results: Superinfection occurred in 34 patients (43%). The mortality rate was 43% with 34 patients, of which 18 had superinfections. A causal association was established between superinfection and hospital stay (OR: 1.56; CI: 95%: 1.26-2.08; p < 0.001), the use of invasive mechanical ventilation (OR: 3.28; CI: 95%: 1.30-8.73; p = 0.014) and the time this procedure was used (OR: 1.37; CI: 95%: 1.15-1.71; p < 0.001). Conclusions: No statistical association was found between mortality and superinfection in the patients under study. There was low presence of coinfections. The stay in the intensive care unit, the use of invasive mechanical ventilation and the time this procedure was used were predictive variables for the occurrence of superinfection.

Transition-Metal Oxides for Kesterite Solar Cells Developed on Transparent Substrates.

Fabrication on transparent soda-lime glass/fluorine-doped tin oxide (FTO) substrates opens the way to advanced applications for kesterite solar cells such as semitransparent, bifacial, and tandem devices, which are key to the future of the PV market. However, the complex behavior of the p-kesterite/n-FTO back-interface potentially limits the power conversion efficiency of such devices. Overcoming this issue requires careful interface engineering. This work empirically explores the use of transition-metal oxides (TMOs) and Mo-based nanolayers to improve the back-interface of Cu2ZnSnSe4, Cu2ZnSnS4, and Cu2ZnSn(S,Se)4 solar cells fabricated on transparent glass/FTO substrates. Although the use of TMOs alone is found to be highly detrimental to the devices inducing complex current-blocking behaviors, the use of Mo:Na nanolayers and their combination with n-type TMOs TiO2 and V2O5 are shown to be a very promising strategy to improve the limited performance of kesterite devices fabricated on transparent substrates. The optoelectronic, morphological, structural, and in-depth compositional characterization performed on the devices suggests that the improvements observed are related to a combination of shunt insulation and recombination reduction. This way, record efficiencies of 6.1, 6.2, and 7.9% are obtained for Cu2ZnSnSe4, Cu2ZnSnS4, and Cu2ZnSn(S,Se)4 devices, respectively, giving proof of the potential of TMOs for the development of kesterite solar cells on transparent substrates.

Progress and Perspectives of Thin Film Kesterite Photovoltaic Technology: A Critical Review.

The latest progress and future perspectives of thin film photovoltaic kesterite technology are reviewed herein. Kesterite is currently the most promising emerging fully inorganic thin film photovoltaic technology based on critical raw-material-free and sustainable solutions. The positioning of kesterites in the frame of the emerging inorganic solar cells is first addressed, and the recent history of this family of materials briefly described. A review of the fast progress achieved earlier this decade is presented, toward the relative slowdown in the recent years partly explained by the large open-circuit voltage (VOC ) deficit recurrently observed even in the best solar cell devices in the literature. Then, through a comparison with the close cousin Cu(In,Ga)Se2 technology, doping and alloying strategies are proposed as critical for enhancing the conversion efficiency of kesterite. In the second section herein, intrinsic and extrinsic doping, as well as alloying strategies are reviewed, presenting the most relevant and recent results, and proposing possible pathways for future implementation. In the last section, a review on technological applications of kesterite is presented, going beyond conventional photovoltaic devices, and demonstrating their suitability as potential candidates in advanced tandem concepts, photocatalysis, thermoelectric, gas sensing, etc.

Resonant Raman scattering based approaches for the quantitative assessment of nanometric ZnMgO layers in high efficiency chalcogenide solar cells.

This work reports a detailed resonant Raman scattering analysis of ZnMgO solid solution nanometric layers that are being developed for high efficiency chalcogenide solar cells. This includes layers with thicknesses below 100 nm and compositions corresponding to Zn/(Zn + Mg) content rations in the range between 0% and 30%. The vibrational characterization of the layers grown with different compositions and thicknesses has allowed deepening in the knowledge of the sensitivity of the different Raman spectral features on the characteristics of the layers, corroborating the viability of resonant Raman scattering based techniques for their non-destructive quantitative assessment. This has included a deeper analysis of different experimental approaches for the quantitative assessment of the layer thickness, based on (a) the analysis of the intensity of the ZnMgO main Raman peak; (b) the evaluation of the changes of the intensity of the main Raman peak from the subjacent layer located below the ZnMgO one; and (c) the study of the changes in the relative intensity of the first to second/third order ZnMgO peaks. In all these cases, the implications related to the presence of quantum confinement effects in the nanocrystalline layers grown with different thicknesses have been discussed and evaluated.

Structural Polymorphism in "Kesterite" Cu2ZnSnS4: Raman Spectroscopy and First-Principles Calculations Analysis.

This work presents a comprehensive analysis of the structural and vibrational properties of the kesterite Cu2ZnSnS4 (CZTS, I4̅ space group) as well as its polymorphs with the space groups P4̅2c and P4̅2m, from both experimental and theoretical point of views. Multiwavelength Raman scattering measurements performed on bulk CZTS polycrystalline samples were utilized to experimentally determine properties of the most intense Raman modes expected in these crystalline structures according to group theory analysis. The experimental results compare well with the vibrational frequencies that have been computed by first-principles calculations based on density functional theory. Vibrational patterns of the most intense fully symmetric modes corresponding to the P4̅2c structure were compared with the corresponding modes in the I4̅ CZTS structure. The results point to the need to look beyond the standard phases (kesterite and stannite) of CZTS while exploring and explaining the electronic and vibrational properties of these materials, as well as the possibility of using Raman spectroscopy as an effective technique for detecting the presence of different crystallographic modifications within the same material.

Role of S and Se atoms on the microstructural properties of kesterite Cu2ZnSn(S(x)Se(1-x))4 thin film solar cells.

Microstructural properties of Cu2ZnSn(S(x)Se(1-x))4 kesterite solid solutions were investigated using grazing incidence X-ray diffraction for the full interval of anion compositions in order to explore the influence of S and Se atoms on the thin film morphology. Thin films were prepared by sputtering deposition of metallic precursors, which were then submitted to a high temperature sulfo-selenization process. By adjusting process parameters samples from sulfur- to selenium-pure (0 ≤ x ≤ 1) were made. Microstructural analysis shows a strong dependence of domain size and microstrain on composition. Both values increase with higher sulfur content, and depth profile analysis by grazing incidence X-ray diffraction shows selenium-rich films tend to have a more homogeneous depth distribution of domain size. The increasing trend in domain size of S-rich absorbers can be related to lower formation energies of the sulfur binary phases leading to formation of kesterites, while the increase in the microstrain is explained by the substitution of larger Se atoms with smaller S atoms in the host lattice and the presence of secondary phases.

Impact of Na Dynamics at the Cu2ZnSn(S,Se)4/CdS Interface During Post Low Temperature Treatment of Absorbers.

Cu2SnZn(S,Se)4 (CZTSSe) solar cells based on earth abundant and nontoxic elements currently achieve efficiencies exceeding 12%. It has been reported that, to obtain high efficiency devices, a post thermal treatment of absorbers or devices at temperatures ranging between 150 and 400 °C (post low temperature treatment, PLTT) is advisable. Recent findings point toward a beneficial passivation of grain boundaries with SnOx or Cu-depleted surface and grain boundaries during the PLTT process, but no investigation regarding alkali doping is available, even though alkali dynamics, especially Na, are systematically reported to be crucial within the field. In this work, CZTSSe absorbers were subjected to the PLTT process under different temperatures, and solar cells were completed. We found surprisingly behavior in which efficiency decreased to nearly 0% at 200 °C during the PLTT process, being recovered or even improved at temperatures above 300 °C. This unusual behavior correlates well with the Na dynamics in the devices, especially with the in-depth distribution of Na in the active CZTSSe/CdS interface region, indicating the key importance of Na spatial distribution on device properties. We present an innovative model for Na dynamics supported by theoretical calculations and additional specially designed experiments to explain this behavior. After optimization of the PLTT process, a Se-rich CZTSSe solar cell with 8.3% efficiency was achieved.

Polarized Raman scattering study of kesterite type Cu2ZnSnS4 single crystals.

A non-destructive Raman spectroscopy has been widely used as a complimentary method to X-ray diffraction characterization of Cu2ZnSnS4 (CZTS) thin films, yet our knowledge of the Raman active fundamental modes in this material is far from complete. Focusing on polarized Raman spectroscopy provides important information about the relationship between Raman modes and CZTS crystal structure. In this framework the zone-center optical phonons of CZTS, which is most usually examined in active layers of the CZTS based solar cells, are studied by polarized resonant and non-resonant Raman spectroscopy in the range from 60 to 500 cm(-1) on an oriented single crystal. The phonon mode symmetry of 20 modes from the 27 possible vibrational modes of the kesterite structure is experimentally determined. From in-plane angular dependences of the phonon modes intensities Raman tensor elements are also derived. Whereas a strong intensity enhancement of the polar E and B symmetry modes is induced under resonance conditions, no mode intensity dependence on the incident and scattered light polarization configurations was found in these conditions. Finally, Lyddane-Sachs-Teller relations are applied to estimate the ratios of the static to high-frequency optic dielectric constants parallel and perpendicular to c-optical axis.

Impact of Sn(S,Se) secondary phases in Cu2ZnSn(S,Se)4 solar cells: a chemical route for their selective removal and absorber surface passivation.

The control and removal of secondary phases is one of the major challenges for the development of Cu2ZnSn(S,Se)4 (CZTSSe)-based solar cells. Although etching processes have been developed for Cu(S,Se), Zn(S,Se), and CuSn(S,Se) secondary phases, so far very little attention has been given to the role of Sn(S,Se). In this paper, we report a chemical route using a yellow (NH4)2S solution to effectively remove Sn(S,Se). We found that Sn(S,Se) can form on the surface either because of stoichiometric deviation or by condensation. After etching, the efficiency of devices typically increases between 20 and 65% relative to the before etch efficiencies. We achieved a maximum 5.9% efficiency in Se-rich CZTSSe-based devices. It is confirmed that this feature is related not only to the removal of Sn(S,Se) but also to the unexpected passivation of the surface. We propose a phenomenological model for this passivation, which may open new perspectives for the development of CZTSSe-based solar cells.

Structural study and Raman scattering analysis of Cu2ZnSiTe4 bulk crystals.

Bulk crystals of Cu(2)ZnSiTe(4) (CZSiTe) have been prepared by modified Bridgman method and have been investigated by single crystal X-ray method, Energy Dispersive X-Ray analysis and Raman scattering techniques. The structural studies revealed that the CZSiTe compounds crystallizes in the tetragonal space group I4¯2m, with a = b = 5.9612(1) Å and c = 11.7887(4) Å at 293 K. The Raman spectrum characteristic of the crystals exhibits nine peaks, with two dominant peaks at approximately 134 cm(-1) and 151 cm(-1) that can be used as fingerprint peaks for the identification of this compound. The Raman peaks were analyzed on the basis of the derived irreducible representation for the zone center phonons and by comparison with experimental and theoretical data from close related semiconductors as Cu(2)FeSnS(4) and Cu(2)ZnSnSe(4).

ZnSe etching of Zn-rich Cu2ZnSnSe4: an oxidation route for improved solar-cell efficiency.

Cu2ZnSnSe4 kesterite compounds are some of the most promising materials for low-cost thin-film photovoltaics. However, the synthesis of absorbers for high-performing devices is still a complex issue. So far, the best devices rely on absorbers grown in a Zn-rich and Cu-poor environment. These off-stoichiometric conditions favor the presence of a ZnSe secondary phase, which has been proved to be highly detrimental for device performance. Therefore, an effective method for the selective removal of this phase is important. Previous attempts to remove this phase by using acidic etching or highly toxic organic compounds have been reported but so far with moderate impact on device performance. Herein, a new oxidizing route to ensure efficient removal of ZnSe is presented based on treatment with a mixture of an oxidizing agent and a mineral acid followed by treatment in an aqueous Na2S solution. Three different oxidizing agents were tested: H2O2, KMnO4, and K2Cr2O7, combined with different concentrations of H2SO4. With all of these agents Se(2-) from the ZnSe surface phase is selectively oxidized to Se(0), forming an elemental Se phase, which is removed with the subsequent etching in Na2S. Using KMnO4 in a H2SO4-based medium, a large improvement on the conversion efficiency of the devices is observed, related to an improvement of all the optoelectronic parameters of the cells. Improvement of short-circuit current density (J(sc)) and series resistance is directly related to the selective etching of the ZnSe surface phase, which has a demonstrated current-blocking effect. In addition, a significant improvement of open-circuit voltage (V(oc)), shunt resistance (R(sh)), and fill factor (FF) are attributed to a passivation effect of the kesterite absorber surface resulting from the chemical processes, an effect that likely leads to a reduction of nonradiative-recombination states density and a subsequent improvement of the p-n junction.

The three A symmetry Raman modes of kesterite in Cu2ZnSnSe4.

We investigate CZTSe films by polarization dependent Raman spectroscopy. The main peaks at 170 cm(-1), and 195 cm(-1) are found to have A symmetry. The Raman signal at 170 cm(-1) is found to be composed of two modes at 168 cm(-1) and 172 cm(-1). We attribute these three Raman peaks to the three A symmetry modes predicted for kesterite ordered Cu(2)ZnSnSe(4). The main Raman peak is asymmetrically broadened towards lower energies. Possible sources of the broadening are tested through temperature and depth dependent measurements. The broadening is attributed to phonon confinement effects related to the presence of lattice defects.

Antimony-based ligand exchange to promote crystallization in spray-deposited Cu2ZnSnSe4 solar cells.

A multistrategy approach to overcome the main challenges of nanoparticle-based solution-processed Cu2ZnSnSe4 thin film solar cells is presented. We developed an efficient ligand exchange strategy, using an antimony salt, to displace organic ligands from the surface of Cu2ZnSnS4 nanoparticles. An automated pulsed spray-deposition system was used to deposit the nanoparticles into homogeneous and crack-free films with controlled thickness. After annealing the film in a Se-rich atmosphere, carbon-free and crystalline Cu2ZnSnSe4 absorber layers were obtained. Not only was crystallization promoted by the complete removal of organics, but also Sb itself played a critical role. The Sb-assisted crystal growth is associated with the formation of a Sb-based compound at the grain boundaries, which locally reduces the melting point, thus promoting the film diffusion-limited crystallization.

Single-step sulfo-selenization method to synthesize Cu2ZnSn(S(y)Se(1-y))4 absorbers from metallic stack precursors.

Pentenary Cu2ZnSn(S(y)Se(1-y))4 (kesterite) photovoltaic absorbers are synthesized by a one-step annealing process from copper-poor and zinc-rich precursor metallic stacks prepared by direct-current magnetron sputtering deposition. Depending on the chalcogen source--mixtures of sulfur and selenium powders, or selenium disulfide--as well as the annealing temperature and pressure, this simple methodology permits the tuning of the absorber composition from sulfur-rich to selenium-rich in one single annealing process. The impact of the thermal treatment variables on chalcogenide incorporation is investigated. The effect of the S/(S+Se) compositional ratio on the structural and morphological properties of the as-grown films, and the optoelectronic parameters of solar cells fabricated using these absorber films is studied. Using this single-step sulfo-selenization method, pentenary kesterite-based devices with conversion efficiencies up to 4.4 % are obtained.

Development of a selective chemical etch to improve the conversion efficiency of Zn-rich Cu2ZnSnS4 solar cells.

Improvement of the efficiency of Cu(2)ZnSnS(4) (CZTS)-based solar cells requires the development of specific procedures to remove or avoid the formation of detrimental secondary phases. The presence of these phases is favored by the Zn-rich and Cu-poor conditions that are required to obtain device-grade layers. We have developed a selective chemical etching process based on the use of hydrochloric acid solutions to remove Zn-rich secondary phases from the CZTS film surface, which are partly responsible for the deterioration of the series resistance of the cells and, as a consequence, the conversion efficiency. Using this approach, we have obtained CZTS-based devices with 5.2% efficiency, which is nearly twice that of the devices we have prepared without this etching process.

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Aspectos eticos y legales de la reproduccion asistida / Ethical and legal aspects of assisted reproduction

La infertilidad constituye un problema que puede afectar a ambos miembros de la pareja. Con el tiempo, el conflicto puede agravarse y llegar a constituir un motivo de disolución del vínculo afectivo, con la repercusion psicosocial que estas rupturas traen aparejadas. Aunque la superpoblación es un problema mucho más apremiante que los transtornos de la reprodución, no por ello estos últimos dejan de ser una preocupación creciente para la sociedad. Con la aplicación a nivel mundial de las nuevas técnicas de reprodución o concepción asistida, han surgido, nuevos y graves problemas de índole ético legal