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The certified power conversion efficiency of state-of-the-art organic–inorganic hybrid perovskite solar cells has surpassed 25%, showing promising potential for commercialization. Compared with vol...

Background Cadmium uptake by cacao plants can affect plant growth, consumer health and commercialisation. To develop mitigation strategies, it is essential to identify the soil characteristics that could influence this absorption. To determine the relationships between cadmium absorption and the soil characteristics of cacao areas, the responses at concentrations of 0, 2, 5, 10 and 20 μg g-1 of cadmium in three soils of these areas and an andisol were evaluated, using 120-day-old seedlings of four cultivars of Theobroma cacao L. Results In the present study, several relationships were found between chemical and physical soil characteristics and available cadmium, such as real and bulk densities, as well as contents of iron, sand, magnesium, potassium, sodium and copper. Additionally, moderate to strong correlations between potassium (r2 = -0.56) and real density (r2 = 0.42), with foliar cadmium, were found. Moreover, a differential deleterious effect on cacao growth in variables such as biomass was corroborated in cadmium concentrations from 5 μg g-1 in soils. There were no statistical differences between cultivars with respect to cadmium uptake or plant growth. Finally, a multiple linear regression model is proposed to estimate the foliar cadmium content (r2 = 0.878). Conclusion Some soil characteristics such as density, as well as sand, clay, aluminium, potassium and iron contents, should be considered before establishing cacao crops to avoid cadmium accumulation. The correlation between potassium with foliar cadmium indicated that potassium could be significant in cadmium uptake mitigation strategies. The high correlation between available cadmium and foliar cadmium indicates that the quantification methodology developed using ethylenediaminetetraacetic acid extractant may be a useful diagnostic tool. © 2021 Society of Chemical Industry.

The commercial feasibility of perovskite solar cells (PSCs) is not guaranteed as long as lead (Pb) is present in the active material, halide perovskites. Mixed halide tin (Sn)-based alloyed perovsk...

Over the past decade, lead halide perovskite materials have emerged as a promising candidate for third-generation solar cells and have progressed extremely rapidly. The tunable band gap, strong absorption, high power conversion efficiency, and low cost of perovskite solar cells makes them highly competitive compared to current commercialized silicon-based and thin film-based photovoltaic technologies. However, commercial products unavoidably result in large amounts of waste and end-of-life devices which can cause serious environmental impacts. To address this issue, recycle and recovery technologies of perovskite solar cells should be researched and developed proactively. In this review, the development of perovskite solar cells and their necessary materials are first introduced. Subsequently, the potential environmental impacts of perovskite solar cells are discussed, including their stability and lifetime, use of critical materials (i.e., indium, tin, and lead), and toxicity. Accordingly, the present recycle and recovery technologies are reviewed, providing information and recommendations of key strategies for recycling and recovering. Finally, future works and strategies for recycling and recovering perovskite solar cells are proposed.

This review focuses on the advancements in stability of perovskite solar cells under stress from ambient moisture, high temperatures, and UV light exposure. Moisture stability has been improved by utilizing several polymeric encapsulation methods, moisture-resistant hole transport layers (HTLs), CF4 plasma treatments, and perovskite grain crosslinking. Fluorinated encapsulation methods have proven especially successful, producing cells that maintained their PCE after 75 days at 50% RH and 5 mW cm−2 of UV radiation. Temperature destabilization has been hypothesized to occur as a result of perovskite phase transitions and the HTL dopant migration to the mesoporous TiO2 surface. Temperature-sensitive perovskites have been stabilized by tuning the Goldschmidt tolerance factor and introducing thermally resistant HTLs embedded in a polymeric matrix with polycarbonate acting as an effective thermal insulating matrix. UV light instabilities have also been shown to occur due to the photocatalysis of TiO2 and the TiO2 perovskite interface. The introduction of a Sb2S3 buffer or CsBr clusters as interface modifiers can stabilize the interface of TiO2 perovskite. Herein, we aim at highlighting the main processes that prevent perovskite degradation using polymers and interfacial modifiers.

One of the organic components in the perovskite photo-absorber, the methylammonium cation, has been suggested to be a roadblock to the long-term operation of organic–inorganic hybrid perovskite-based solar cells. In this work we systematically explore the crystallographic and optical properties of the compositional space of mixed cation and mixed halide lead perovskites, where formamidinium (FA+) is gradually replaced by cesium (Cs+), and iodide (I−) is substituted by bromide (Br−), i.e., CsyFA1−yPb(BrxI1−x)3. Higher tolerance factors lead to more cubic structures, whereas lower tolerance factors lead to more orthorhombic structures. We find that while some correlation exists between the tolerance factor and structure, the tolerance factor does not provide a holistic understanding of whether or not a perovskite structure will fully form. By screening 26 solar cells with different compositions, our results show that Cs1/6FA5/6PbI3 delivers the highest efficiency and long-term stability among the I-rich compositions. This work sheds light on the fundamental structure–property relationships in the CsyFA1−yPb(BrxI1−x)3 compositional space, providing vital insight to the design of durable perovskite materials. Our approach provides a library of structural and optoelectronic information for this compositional space.

Resumen Introducción. Staphylococcus aureus resistente a la meticilina (SARM) es un microorganismo que coloniza las fosas nasales y diferentes partes del cuerpo, lo cual se considera un factor de riesgo para adquirir infecciones invasivas, especialmente en pacientes sometidos a cirugía cardiovascular. Objetivo. Determinar la colonización nasal por SARM y establecer las características clínicas en pacientes programados para cirugía cardiovascular. Materiales y métodos. Se hizo un estudio descriptivo entre febrero y diciembre de 2015. Se incluyeron pacientes adultos programados para cirugía cardiovascular en el Hospital Universitario San Ignacio de Bogotá. La colonización se identificó mediante reacción en cadena de la polimerasa (Polymerase Chain Reaction, PCR) en tiempo real en muestras obtenidas mediante hisopados nasales. Los pacientes fueron descolonizados con mupirocina al 2,0 % intranasal dos veces al día y baños con gluconato de clorhexidina al 4 % del cuello hacía abajo durante cinco días, al cabo de lo cual se hizo una PCR de control. Resultados. Se incluyeron 141 pacientes, 52 hospitalizados y 89 ambulatorios. Del total, 19 (13,4 %) tenían colonización nasal por SARM, correspondientes a 9 (17,3 %) de los 52 hospitalizados y 10 (11,2 %) de los 89 ambulatorios. Todos los pacientes sometidos a descolonización tuvieron resultado negativo en la PCR al final del proceso y ninguno presentó infección del sitio operatorio por S. aureus. Conclusiones. Se demostró colonización nasal por SARM tanto en los pacientes hospitalizados como en los ambulatorios. La descolonización con mupirocina fue efectiva para erradicar el estado de portador a corto plazo, lo que podría tener efecto en las tasas de infección del sitio operatorio en las cirugías cardiovasculares. Abstract Introduction: Methicillin-resistant Staphylococcus aureus (MRSA) is a microorganism that colonizes nostrils and different parts of the body, which is considered a risk factor to acquire invasive infections, especially in cardiovascular surgery patients. Objective: To determine the frequency of nasal colonization by MRSA and to establish the clinical characteristics in patients scheduled for cardiovascular surgery. Materials and methods: This was a descriptive study conducted between February and December, 2015. We included adult patients scheduled for cardiovascular surgery at the Hospital Universitario San Ignacio in Bogotá, Colombia. Colonization was identified by real-time PCR from nasal swabs. Colonized patients were treated with mupirocin 2.0% intranasally twice a day and bathed with chlorhexidine 4% from the neck downwards for five days. At the end of this treatment, PCR control was carried out. Results: We included 141 patients with a percentage of nasal colonization of 13.4% (19/141). There were 52 hospitalized patients and 89 outpatients with a percentage of nasal colonization of 17.3% (9/52), and 11.2% (10/89), respectively. All colonized patients who received treatment had a negative PCR at the end of the regime and none of the participating patients had a surgical site infection by S. aureus at the end of the study. Conclusions: Nasal colonization was observed both in hospitalized patients and outpatients. Decolonization treatment with mupirocin was effective to eradicate the carrier state in the short term, which could impact the rates of surgical wound infection associated with cardiovascular surgery.

Perovskite solar cells have been at the center of intense research over the past decade. Efficiencies have gone from single digits to a certified 25.2%, an unprecedented improvement for any solar cell technology. At this stage, stability remains a concern regarding the suitability of these solar cells for commercialization. Here, we review recent developments in the use of carbon materials to improve the stability of perovskite solar cells. Incorporating carbon materials into perovskite solar cells promises to be revolutionary in the solar cell field, as degradation mechanisms are alleviated to achieve long-term stability making them attractive for commercialization.

Background: One of the most used and effective preservation strategies in foods is drying. However, there are problems with the rheological properties, color, and viability of lactic acid bacteria in the yogurt once reconstituted when applying such conservation strategies. Objectives: Determine the concentration of the type of texture improver and drying that minimizes the negative effect on the rheological, color, and microbiological properties of a reconstituted yogurt powder. Methods: Intended to determine the texture improver which increases rheological properties of reconstituted yogurt powder, a mixture type experimental design was applied where three texture improvers were assessed; carboxymethylcellulose (CMC) (mass fraction 0 - 1), pectin (mass fraction 0 - 1), and xanthan gum (mass fraction 0 - 1). The rheological parameters; consistency index (K), flow behavior (n), viscosity at 100s-1 (η), the storage (G') and loss (G'') modules, and the phase shift angle (δ) of each of the reconstitutions were considered as design-dependent variables. Secondly, a central composite design (face-centered) was used for assessing the effectiveness of the drying (convection, spray-drying, and freeze-drying), the concentration of the texture improver (0.0 - 1.0 %), and the yogurt powder concentration (8.0 - 15.0 %). The above-mentioned rheological parameters, color, and viability of the lactic acid bacteria from each reconstituted yogurt powder were considered as the dependent variables. Optimization sought to match the parameters of reconstituted yogurt powder that approximated the conditions of fresh yogurt. Results: The independent variables in their lineal expression and some interactions between them had statistically significant differences (p < 0.05). At a concentration of 10.59 % with 0.03 % xanthan gum, the reconstitution of freeze-dried yogurt powder was the optimized condition (p < 0.05) and obtained the rheological, color, and microbiological parameters closest to fresh yogurt. Conclusions: The drying of the yogurt by freeze-drying mixed with xanthan gum as a texture improver allowed to obtain a reconstituted yogurt with properties close to the fresh product for direct consumption. Resumen Antecedentes: Una de las estrategias de conservación más utilizadas y efectivas en los alimentos es el secado. Sin embargo, existen problemas en las propiedades reológicas, el color y la viabilidad de bacterias ácido lácticas en el yogur una vez reconstituido al aplicar tales estrategias de conservación. Objetivos: Determinar la concentración del tipo de mejorador de textura y secado que minimiza el efecto negativo sobre las propiedades reológicas, de color y microbiológicas de un yogur en polvo reconstituido. Métodos: Para determinar el mejorador de textura que aumente las propiedades reológicas del yogur en polvo reconstituido, se aplicó un diseño experimental de tipo de mezcla donde se evaluaron tres mejoradores de textura; carboximetilcelulosa (CMC) (fracción de masa 0 -1), pectina (fracción de masa 0 -1) y goma xantan (fracción de masa 0 -1); los parámetros reológicos: índice de consistencia (K), comportamiento de flujo (n), viscosidad a 100s-1 (η), módulos de almacenamiento (G ') y pérdida (G' '), y ángulo de desfase (δ) de cada una de las reconstituciones fueron considerados como variables dependientes. En segundo lugar, se utilizó un diseño central compuesto (centrado a las caras) para evaluar el efecto del tipo de secado (convección, secado por aspersión y liofilización), la concentración del mejorador de textura (0.0 - 1.0 %) y concentración del yogur en polvo (8.0 - 15.0 %). Como variables dependientes se consideraron los parámetros reológicos mencionados anteriormente, el color y la viabilidad de las bacterias ácido lácticas de cada yogur en polvo reconstituido. La optimización buscó igualar los parámetros del yogur en polvo reconstituido que se aproximaran a las condiciones del yogur fresco. Resultados: Las variables independientes en su expresión lineal y algunas interacciones entre ellas tuvieron diferencias estadísticamente significativas (p < 0.05). La reconstitución de yogur liofilizado en polvo a una concentración de 10.59 % con 0.03 % de goma xantan, fueron las condiciones optimizadas (p < 0.05) que obtuvieron los parámetros reológicos, de color y microbiológicos más cercanos al yogur fresco. Conclusión: El secado del yogur por liofilización mezclado con goma xantan como mejorador de la textura, permitió obtener un yogur reconstituido con propiedades cercanas al producto fresco para consumo directo.

Summary We investigate the rubrene triplet sensitization by perovskite thin films based on methylammonium formamidinium lead triiodide (MAFA) of varying thicknesses. The power-law dependence of both the MAFA photoluminescence (PL) intensity and upconverted emission is tracked as a function of the incident power density. Bimolecular triplet-triplet annihilation (TTA) exhibits a unique power-law dependence with a slope change from quadratic-to-linear at the threshold Ith. The underlying MAFA PL power-law dependence dictates the power law of the upconverted PL: (1) below Ith, the slope of the upconverted PL is twice the value of the MAFA PL; (2) above Ith, it follows the same power law as the underlying recombination of mobile electrons and holes in the MAFA films. We find that the Ith shifts to subsolar incident laser powers when increasing the MAFA thickness above 30 nm. For the thickest MAFA film of 380 nm we find an upconversion threshold of Ith = 7.1 mW/cm2.

In this study, the efficiency of gaseous ozone (O3) injected in the soil as an oxidizing agent for the inactivation of F. oxysporum was evaluated under laboratory conditions. The results sh...

The role electron-transport layers (ETLs) play in perovskite solar cells (PSCs) is still widely debated. Conduction band alignment at the perovskite/ETL interface has been suggested to be an import...

This paper presents the design, development and preliminary results of a sensor system that georeferences and measures atmospheric variables, polluting gases and particle pollution on ground level and lower troposphere using an unmanned aerial vehicle. The system can measure dioxide and monoxide of carbon, methane, ozone, different-diameter particle pollution, and variables such as temperature, humidity, among others. Data is registered and processed by a microcontroller system, is saved in a SD card and sent to a ground station using an Xtend radiofrequency system. Atmospheric and pollution data is published in real time on a website; reports could be generated. Some tests were performed in Envigado, Antioquia-Colombia, because the special geographic characteristics of this area increase the concentration of polluting gases in Medellin City troposphere. This equipment facilitates terrestrial and aerial measurements because is a compact and versatile device that allows optimizing predictive models of pollutant gases.

Cheese is considered one of the most important products from milk production worldwide, and its world production has long been growing due to the high and constant demand for dairy products. However, cheese yield has always been a main problematic for cheesemakers from an economic viewpoint because of low values. This research aimed to determine the effect of the type of enzyme and its addition time on the composition, yields, texture, and microstructure of a semi-soft fresh cheese. A multi-factor categorical design was used. Type of enzyme: transglutaminase at 10 g/100L, phospholipase at 6.52 mL/100L, or the interaction between them. And, its time addition were: before, simultaneously or after the addition of rennet. The type of enzyme and its addition time affect statistically the chemical composition of the cheese, yield and texture. Whereas, the addition of transglutaminase together with phospholipase after rennet showed the highest moisture-adjusted yield cheese value (Yma:15.460 g/100L). It is worth noting that an increase of up to 3.89% in the yield was achieved when transglutaminase and phospholipase were used. The addition of transglutaminase together with phospholipase after rennet presented most of the best adjusted yields, suggesting an economical application of the enzyme in cheese making.

This study explores the reprocessing behavior of polypropylene-sugarcane bagasse biocomposites using neat and chemically treated bagasse fibers (20 wt.%). Biocomposites were reprocessed 5 times using the extrusion process followed by injection molding. The mechanical properties indicate that microfibers bagasse fibers addition and chemical treatments generate improvements in the mechanical properties, reaching the highest performance in the third cycle where the flexural modulus and flexural strength increase 57 and 12% in comparison with neat PP. differential scanning calorimetry (DSC) and TGA characterization show that bagasse fibers addition increases the crystallization temperature and thermal stability of the biocomposites 7 and 39 &deg, C respectively, without disturbing the melting process of the PP phase for all extrusion cycles. The rheological test shows that viscosity values of PP and biocomposites decrease progressively with extrusion cycles, however, Cole&ndash, Cole plots, dynamic mechanical analysis (DMA), width at half maximum of tan delta peaks and SEM micrographs show that chemical treatments and reprocessing could improve fiber dispersion and fiber&ndash, matrix interaction. Based on these results, it can be concluded that recycling potential of polypropylene-sugarcane bagasse biocomposites is huge due to their mechanical, thermal and rheological performance resulting in advantages in terms of sustainability and life cycle impact of these materials.

In this study, the properties of a polyolefin blend matrix (PP-HDPE) were evaluated and modified through the addition of raw coir coconut fibers-(CCF). PP-HDPE-CCF biocomposites were prepared using melt blending processes with CCF loadings up to 30% (w/w). CCF addition generates an increase of the tensile and flexural modulus up to 78% and 99% compared to PP-HDPE blend. This stiffening effect is caused by a decrease in the polymeric chain mobility due to CCF, the higher mechanical properties of the CCF compared to the polymeric matrix and could be an advantage for some biocomposites applications. Thermal characterizations show that CCF incorporation increases the PP-HDPE thermal stability up to 63 &deg, C, slightly affecting the melting behavior of the PP and HDPE matrix. DMA analysis shows that CCF improves the PP-HDPE blend capacity to absorb higher external loads while exhibiting elastic behavior maintaining its characteristics at higher temperatures. Also, the three-dimensional microscopy study showed that CCF particles enhance the dimensional stability of the PP-HDPE matrix and decrease manufacturing defects as shrinkage in injected specimens. This research opens a feasible opportunity for considering PP-HDPE-CCF biocomposites as alternative materials for the design and manufacturing of sustainable products by injection molding.

Halide perovskites are a strong candidate for the next generation of photovoltaics. Chemical doping of halide perovskites is an established strategy to prepare the highest efficiency and most stable perovskite-based solar cells. In this study, we unveil the doping mechanism of halide perovskites using a series of alkaline earth metals. We find that low doping levels enable the incorporation of the dopant within the perovskite lattice, whereas high doping concentrations induce surface segregation. The threshold from low to high doping regime correlates to the size of the doping element. We show that the low doping regime results in a more n-type material, while the high doping regime induces a less n-type doping character. Our work provides a comprehensive picture of the unique doping mechanism of halide perovskites, which differs from classical semiconductors. We proved the effectiveness of the low doping regime for the first time, demonstrating highly efficient methylammonium lead iodide based solar cells in both n-i-p and p-i-n architectures.

The commercial feasibility of perovskite solar cells (PSCs) is not guaranteed as long as lead (Pb) is present in the active material, halide perovskites. Mixed halide Tin (Sn)-based alloyed perovskites with optimal band gaps ranging from 1.15 to 3.55 eV are excellent alternatives to Pb-based perovskites. In this work, we find that the addition of bulky phenylethyl ammonium (PEA) cation in the precursor solution leads to improved solar cell performance and optoelectronic properties. A prolonged laser exposure is found to induce a redshift the sample absorption for the control and no shift for the PEA-added sample, as shown by transient absorption spectroscopy. Further, we show that the addition of PEA improves band alignment of the perovskite with phenyl-C61-butyric acid methyl ester (PCBM), which aids in electron injection and therefore increases photocurrents in solar cells. These results show that PEA addition suppresses halide segregation improving material stability, charge collection at perovskite/electron transport layer, and recombination dynamics in perovskite material. As a result, the PEA-containing Sn-rich PSCs exhibited a champion efficiency of 13% with a high open-circuit voltage of 0.77 V and improved current-voltage hysteretic behavior. These results shed light on the importance of halide segregation and band alignment when designing lead-free PSCs.

Bismuth-based materials have been studied as alternatives to lead-based perovskite materials for photovoltaic applications. However, poor film quality has limited device performance. In this work, we developed a solvent-engineering method and show that it is applicable to several bismuth-based compounds. Through this method, we obtained compact films of methylammonium bismuth iodide (MBI), cesium bismuth iodide (CBI), and formamidinium bismuth iodide (FBI). On the basis of film growth theory and experimental analyses, we propose a possible mechanism of film formation. Additionally, we demonstrate that the resultant compact MBI film is more suitable to fabricate efficient and stable photovoltaic devices compared to baseline MBI films with pinholes. We further employed a new hole-transporting material to reduce the valence-band offset with the MBI. The best-performing photovoltaic device exhibits an open-circuit voltage of 0.85 V, fill factor of 73%, and a power conversion efficiency of 0.71%, the highest r...

Light- and elevated temperature-induced degradation (LeTID) is a detrimental effect observed under operating conditions in p-type multicrystalline silicon (mc-Si) solar cells. In this contribution, we employ synchrotron-based techniques to study the dissolution of precipitates due to different firing processes at grain boundaries in LeTID-affected mc-Si. The synchrotron measurements show clear dissolution of collocated metal precipitates during firing. We compare our observations with degradation behavior in the same wafers. The experimental results are complemented with process simulations to provide insight into the change in bulk point defect concentration due to firing. Several studies have proposed that LeTID is caused by metal-rich precipitate dissolution during contact firing, and we find that the solubility and diffusivity are promising screening metrics to identify metals that are compatible with this hypothesis. While slower and less soluble elements (e.g., Fe and Cr) are not compatible according to our simulations, the point defect concentrations of faster and more soluble elements (e.g., Cu and Ni) increase after a high-temperature firing process, primarily due to emitter segregation rather than precipitate dissolution. These results are a useful complement to lifetime spectroscopy techniques, and can be used to evaluate additional candidates in the search for the root cause of LeTID.

Although methylammonium lead iodide (MAPI) perovskite solar cells have reached efficiencies above 20%, the material is environmentally unstable. Mixing MAPI with lower dimensional (LD) perovskites has been suggested to improve its stability in recent studies. However, the LD-mixed perovskites have lower device performance, likely as a result of limited charge-carrier mobility due to their decreased structural dimensionality. To understand this effect, we mixed large-A-site cation LD perovskites, tert-butylammonium lead iodide, with MAPI, and performed a device performance diagnostics. The results suggested although the charge-carrier lifetime was improved, the mobility decreased by a factor of 20. This contributed to a reduction in device efficiency by 2 orders of magnitude, indicating that mobility plays an important role in 3D/LD perovskite mixtures.

One of the key properties of lead-halide perovskites employed in solar cells is the defect tolerance of the materials, in particular regarding intrinsic point defects, which mainly form shallow traps. Considering that high luminescence yields and photovoltaic performance are obtained by simple solution processing from commercial chemicals, it is commonly anticipated that the defect tolerance-at least to a considerable degree-extends to grain boundaries and extrinsic defects, i.e. impurities, as well. However, the effect of impurities has hardly been investigated. Here, we intentionally introduce small quantities of bismuth (10 ppm to 2%) in solution to be incorporated in the perovskite films based on mixed cation mixed anion compositions. We observe that Bi impurities in the %-regime reduce charge carrier collection efficiency and, more importantly, that the open-circuit voltage decreases systematically with impurity concentration even in the ppm regime. This strong defect intolerance against Bi impurities comes along with reduced electroluminescence yields and charge carrier lifetimes obtained from transient photoluminescence experiments. Calculations based on molecular dynamics and density functional theory predict delocalized (≈0.16 eV) and localized deep (≈0.51 eV) trap states dependent on the structural arrangement of the surrounding atoms. Structural characterization supports the idea of Bi being present as a homogeneously spread point defect, which substitutes the Pb2+ by Bi3+ as seen from XPS and a reduction of the lattice parameter in XRD. Sensitive measurements of the photocurrent (by FTPS) and surface photovoltage (SPV) confirm the presence of tail states. Photoelectron spectroscopy measurements show evidence of a deep state. These results are consistent with the common idea of shallow traps being responsible for the reduced charge collection efficiency and the decreased fill factor, and deeper traps causing a substantial reduction of the open-circuit voltage. As Bi is only one potential impurity in the precursor salts used in perovskite solar cell fabrication, our findings open-up a research direction focusing on identifying and eliminating impurities that act as recombination centers-a topic that has so far not been fully considered in device optimization studies. Fil: Yavari, M.. École Polytechnique Fédérale de Lausanne; Suiza Fil: Ebadi, Firouzeh. École Polytechnique Fédérale de Lausanne; Suiza Fil: Meloni, Simone. Università di Roma; Italia Fil: Wang, Zishuai. École Polytechnique Fédérale de Lausanne; Suiza Fil: Yang, Terry Chien-Jen. École Polytechnique Fédérale de Lausanne; Suiza Fil: Sun, Shijing. Massachusetts Institute Of Technology; Estados Unidos Fil: Schwartz, Heidi. University Of Cologne; Alemania Fil: Wang, Zaiwei. École Polytechnique Fédérale de Lausanne; Suiza Fil: Niesen, Bjoern. École Polytechnique Fédérale de Lausanne; Suiza Fil: Durantini, Javier Esteban. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; Argentina Fil: Rieder, Philipp. Julius Maximilian University Of Würzburg; Alemania Fil: Tvingstedt, Kristofer. Julius Maximilian University Of Würzburg; Alemania Fil: Buonassisi, Tonio. Massachusetts Institute Of Technology; Estados Unidos Fil: Choy, Wallace C.H.. The University Of Hong Kong; Hong Kong Fil: Filippetti, Alessio. Università Di Cagliari; Italia Fil: Dittrich, Thomas. Helmholtz Center Berlin For Materials And Energy; Alemania Fil: Olthof, Selina. University Of Cologne; Alemania Fil: Correa Baena, Juan Pablo. Massachusetts Institute Of Technology; Estados Unidos Fil: Tress, Wolfgang. École Polytechnique Fédérale de Lausanne; Suiza

Lead halide-based perovskite thin films have attracted great attention due to the explosive increase in perovskite solar cell efficiencies. The same optoelectronic properties that make perovskites ideal absorber materials in solar cells are also beneficial in other light-harvesting applications and make them prime candidates as triplet sensitizers in upconversion via triplet-triplet annihilation in rubrene. In this contribution, we take advantage of long carrier lifetimes and carrier diffusion lengths in perovskite thin films, their high absorption cross sections throughout the visible spectrum, as well as the strong spin-orbit coupling owing to the abundance of heavy atoms to sensitize the upconverter rubrene. Employing bulk perovskite thin films as the absorber layer and spin-mixer in inorganic/organic heterojunction upconversion devices allows us to forego the additional tunneling barrier owing from the passivating ligands required for colloidal sensitizers. Our bilayer device exhibits an upconversion efficiency in excess of 3% under 785 nm illumination.

The same optical and electronic properties that make perovskite thin films ideal absorber materials in photovoltaic applications are also beneficial in photon upconversion devices. In this contribution, we investigate the rubrene-triplet sensitization by perovskite thin films based on methylammonium formamidinium lead triiodide (MAFA). To elucidate the role of trap states which affect the free carrier lifetimes, we fabricate MAFA perovskite thin films with three different thicknesses. By measuring the change in the photoluminescence properties under different excitation fluences, we find that the prevalent recombination mechanism shifts from monomolecular for thinner films to bimolecular recombination for thicker MAFA films, indicating a reduction in shallow trap-assisted recombination. The addition of rubrene shows a passivating effect on the MAFA surface, but adds an additional quenching pathway due to charge transfer to the triplet state of rubrene. We observe that the threshold for efficient triplet-triplet annihilation shifts to lower incident powers with increasing MAFA thickness, which suggests that the charge transfer to the triplet state competes with non-radiative trap filling. Hence, injection of free electrons and holes into the upconverting organic semiconductor can provide a new avenue for sensitization of rubrene, and may allow us to move away from the necessity of efficient excitonic singlet-to-triplet converters.

Photovoltaic (PV) cells have the potential to serve as on-board power sources for low-power IoT devices. Here, we explore the use of perovskite solar cells to power Radio Frequency (RF) backscatter-based IoT devices with few $\mu \text{W}$ power demand. Perovskites are suitable for low-cost, high-performance, low-temperature processing, and flexible light energy harvesting that hold the possibility to significantly extend the range and lifetime of current backscatter techniques such as Radio Frequency Identification (RFID). For these reasons, perovskite solar cells are prominent candidates for future low-power wireless applications. We report on realizing a functional perovskite-powered wireless temperature sensor with 4 m communication range. We use a 10.1% efficient perovskite PV module generating an output voltage of 4.3 V with an active area of 1.06 cm2 under 1 sun illumination, with AM 1.5G spectrum, to power a commercial off-the-shelf RFID IC, requiring 10 – 45 $\mu \text{W}$ of power. Having an on-board energy harvester provides extra-energy to boost the range of the sensor (5 $ \times $ ) in addition to providing energy to carry out high-volume sensor measurements (hundreds of measurements per min). Our evaluation of the prototype suggests that perovskite photovoltaic cells are able to meet the energy needs to enable fully power-autonomous low-power RF backscatter applications of the future. We conclude with an outlook into a range of applications that we envision to leverage the synergies offered by combining perovskite photovoltaics and RFID.

In this work, biocomposites based on recycled polypropylene (r-PP) and two different natural fibers (coffee husk-CHF and coconut coir-CCF fibers) were prepared using extrusion and injection molding processes. Also, the addition of maleated polypropylene (MAPP) as a coupling agent on the biocomposites was explored. Recycled polypropylene and its biocomposites were tested following ASTM standards in order to evaluate tensile and flexural mechanical properties. Also, thermal behavior and the morphology of these materials have been studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and scanning electronic microscopy (SEM). The experimental results showed that the addition of CHF and CCF to the r-PP resulted in an increase in the flexural modulus and thermal properties of the composites but resulted in poor impact properties. Thermal characterization showed that CHF possesses a better thermal stability compared to CCF. However, both fibers act as nucleating agents and generate an increase in the thermal stability of the r-PP phase. Finally, it was observed that addition of 4% of MAPP significantly improved the mechanical strength and impact behavior of the biocomposites. Regarding environmental issues, a cradle to gate life cycle assessment was made in order to define the carbon footprint of the materials.

Triarylamine-based polymers with different functional groups were synthetized as hole-transport materials (HTMs) for perovskite solar cells (PSCs). The novel materials enabled efficient PSCs without the use of chemical doping (or additives) to enhance charge transport. Devices employing poly(triarylamine) with methylphenylethenyl functional groups (V873) showed a power conversion efficiency of 12.3 %, whereas widely used additive-free poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) demonstrated 10.8 %. Notably, devices with V873 enabled stable PSCs under 1 sun illumination at maximum power point tracking for approximately 40 h at room temperature, and in the dark under elevated temperature (85 °C) for more than 140 h. This is in stark contrast to additive-containing devices, which degrade significantly within the same time frame. The results present remarkable progress towards stable PSC under real working conditions and industrial stress tests.

Terrestrial applications of solar cells during day–night cycling as well as operation in winter and summer involve substantial temperature variations, which influence the photophysics as well as the charge separation and transport properties in the various materials employed in a device. In this study, the optical absorption of methylammonium lead iodide (MAPbI3) and the device performance of MAPbI3 solar cells have been investigated in an extended temperature range between −190 and 80 °C. The optical properties were found to change by only a small amount in that temperature range. The device performance did, however, show more dramatic changes and decreased in a reversible manner for temperatures both higher and lower than room temperature. For temperatures up to 80 °C and down to −80 °C, the drop in performance was up to 25% compared to the room temperature value. Given thermal stability and reversible device performance, this is probably not a showstopper for terrestrial applications of perovskite sola...

Aerogels of SnO2 were synthesized by an epoxide-initiated sol–gel method. Using ammonium fluoride in the precursor solution allowed for tunability of the aerogel morphology while no change in the conductivity was measured. In particular, aerogel shrinkage was decreased dramatically by the addition of the fluoride precursor. Unfluorinated aerogels showed severe shrinkage of 43% volume change upon supercritical drying compared to the original alcogel volume. Fluorinated samples exhibited a much less pronounced shrinkage at 7%. Multiple characterization methods converged to reveal the mechanism by which fluoride enables the morphological tunability. These findings enable the casting of SnO2 aerogels as thin films (which in the absence of fluoride these crack and delaminate due to shrinkage), opening potential uses in many optoelectronic devices including solar cells.

Tandem solar cells combining silicon and perovskite absorbers have the potential to outperform state-of-the-art high efficiency silicon single junction devices. However, the practical fabrication of monolithic silicon/perovskite tandem solar cells is challenging as material properties and processing requirements such as temperature restrict the device design. Here, we fabricate an 18% efficient monolithic tandem cell formed by a silicon heterojunction bottom-and a perovskite top-cell enabling a very high open circuit voltage of 1.78 V. The monolithic integration was realized via low temperature processing of the semitransparent perovskite sub-cell where an energetically aligned electron selective contact was fabricated by atomic layer deposition of tin oxide. The hole selective, transparent top contact was formed by a stack of the organic hole transport material spiro-OMeTAD, molybdenum oxide and sputtered indium tin oxide. The tandem cell design is currently limited by the photo-current generated in the silicon bottom cell that is reduced due to reflectance losses. Based on optical modelling and first experiments, we show that these losses can be significantly reduced by combining optical optimization of the device architecture including light trapping approaches.

Mixed-ion (FAPbI(3))(1-x)(MAPbBr(3))(x) perovskite solar cells have achieved power conversion efficiencies surpassing 20%. However, in order to obtain these high efficiencies the preparation is performed in a controlled inert atmosphere. Here, we report a procedure for manufacturing highly efficient solar cells with a mixed-ion perovskite in ambient atmosphere. By including a heating step at moderate temperatures of the mesoporous titanium dioxide substrates, and spin-coating the perovskite solution on the warm substrates in ambient air, a red intermediate phase is obtained. Annealing the red phase at 100 degrees C results in a uniform and crystalline perovskite film, whose thickness is dependent on the substrate temperature prior to spin-coating. The temperature was optimized between 20 and 100 degrees C and it was observed that 50 degrees C substrate temperature yielded the best solar cell performances. The average efficiency of the best device was 17.6%, accounting for current-voltage (I-V) measurement hysteresis, with 18.8% performance in the backward scan direction and 16.4% in the forward scan direction. Our results show that it is possible to manufacture high-efficiency mixed-ion perovskite solar cells under ambient conditions, which is relevant for large-scale and low-cost device manufacturing processing.

Lead halide perovskites have attracted considerable interest as photoabsorbers in PV-applications over the last few years. The most studied perovskite material achieving high photovoltaic performance has been methyl ammonium lead iodide, CH3NH3PbI3. Recently the highest solar cell efficiencies have, however, been achieved with mixed perovskites where iodide and methyl ammonium partially have been replaced by bromide and formamidinium. In this work, the mixed perovskites were explored in a systematic way by manufacturing devices where both iodide and methyl ammonium were gradually replaced by bromide and formamidinium. The absorption and the emission behavior as well as the crystallographic properties were explored for the perovskites in this compositional space. The band gaps as well as the crystallographic structures were extracted. Small changes in the composition of the perovskite were found to have a large impact on the properties of the materials and the device performance. In the investigated compositional space, cell efficiencies, for example, vary from a few percent up to 20.7%. From the perspective of applications, exchanging iodide with bromide is especially interesting as it allows tuning of the band gap from 1.5 to 2.3 eV. This is highly beneficial for tandem applications, and an empirical expression for the band gap as a function of composition was determined. Exchanging a small amount of iodide with bromide is found to be highly beneficial, whereas a larger amount of bromide in the perovskite was found to cause intense sub band gap photoemission with detrimental results for the device performance. This could be caused by the formation of a small amount of an iodide rich phase with a lower band gap, even though such a phase was not observed in diffraction experiments. This shows that stabilizing the mixed perovskites will be an important task in order to get the bromide rich perovskites, which has a higher band gap, to reach the same high performance obtained with the best compositions.

Perovskite solar cells are one of the most promising photovoltaic technologies with their extraordinary progress in efficiency and the simple processes required to produce them. However, the frequent presence of a pronounced hysteresis in the current voltage characteristic of these devices arises concerns on the intrinsic stability of organo-metal halides, challenging the reliability of technology itself. Here, we show that n-doping of mesoporous TiO2 is accomplished by facile post treatment of the films with lithium salts. We demonstrate that the Li-doped TiO2 electrodes exhibit superior electronic properties, by reducing electronic trap states enabling faster electron transport. Perovskite solar cells prepared using the Li-doped films as scaffold to host the CH3NH3PbI3 light harvester produce substantially higher performances compared with undoped electrodes, improving the power conversion efficiency from 17 to over 19% with negligible hysteretic behaviour (lower than 0.3%)., Perovskite solar cells are still plagued by hysteresis, despite the good charge transport properties of the perovskite counterpart. Here, the authors dope the mesoporous TiO2 scaffold with lithium to improve the transport properties of this other important component of solar cells, and reduce the hysteresis.

The hormone ABA regulates the oxidative stress state under desiccation in seaweed species; an environmental condition generated during daily tidal changes. Desiccation is one of the most important factors that determine the distribution pattern of intertidal seaweeds. Among most tolerant seaweed is Pyropia orbicularis, which colonizes upper intertidal zones along the Chilean coast. P. orbicularis employs diverse mechanisms of desiccation tolerance (DT) (among others, e.g., antioxidant activation, photoinhibition, and osmo-compatible solute overproduction) such as those used by resurrection plants and bryophytes. In these organisms, the hormone abscisic acid (ABA) plays an important role in regulating responses to water deficit, including gene expression and the activity of antioxidant enzymes. The present study determined the effect of ABA on the activation of antioxidant responses during desiccation in P. orbicularis and in the sensitive species Mazzaella laminarioides and Lessonia spicata. Changes in endogenous free and conjugated ABA, water content during the hydration-desiccation cycle, enzymatic antioxidant activities [ascorbate peroxidase (AP), catalase (CAT) and peroxiredoxine (PRX)], and levels of lipid peroxidation and cell viability were evaluated. The results showed that P. orbicularis had free ABA levels 4-7 times higher than sensitive species, which was overproduced during water deficit. Using two ABA inhibitors (sodium tungstate and ancymidol), ABA was found to regulate the activation of the antioxidant enzymes activities during desiccation. In individuals exposed to exogenous ABA the enzyme activity increased, concomitant with low lipid peroxidation and high cell viability. These results demonstrate the participation of ABA in the regulation of DT in seaweeds, and suggest that regulatory mechanisms with ABA signaling could be of great importance for the adaptation of these organisms to dehydration.

By harvesting sub-bandgap photons, we have a path to overcome the Shockley-Queisser limit in photovoltaics (PVs). We investigate semiconductor nanocrystal (NC) sensitized upconversion via triplet-triplet annihilation (TTA) in organic semiconductors (OSCs). Since this process relies on optically inactive triplet states in the OSCs, we utilize PbS NCs to directly sensitize the triplet state via energy transfer. This is possible due to the strong spin-orbit coupling in PbS NCs, resulting in rapid spin-dephasing of the exciton. Current technology allows for upconversion of light with a photon energy above $\sim 1.1$ eV. However, while internal efficiencies are rapidly improving, the low external device efficiencies render them impractical for applications, as devices are based on a single monolayer of NCs. Our results show simply increasing the PbS NC film thickness does not show improvement in the efficiency due to poor exciton transport between PbS NCs. Here, we present a new strategy to increase the external upconversion efficiency by utilizing thin tinbased halide perovskites as the absorbing layer. Resonant energy transfer from the perovskite to the PbS NCs allows for subsequent sensitization of the triplet state in rubrene.

Perovskite solar cells (PSCs) are very promising lab-scale technologies to deliver inexpensive solar electricity. Low-temperature, planar PSCs are of particularly interest for large-scale deployment due to their inherent suitability for flexible substrates and potential for silicon/perovskite tandems. So far, planar PSCs have been prone to large current-voltage hysteresis and low stabilized power output due to a number of issues associated with this kind of device configuration. We find that the suppression of the yellow-phase impurity (∂-FAPbI3) present in formamidium-based perovskites, by RbI addition, contributes to low hysteresis, higher charge carrier mobility, long-lived carrier lifetimes and a champion stabilized power output of 20.3% using SnOx as the electron selective contact. We study the effects of these impurities on the transient behavior that defines hysteresis and its relation to ionic movement. In addition, we find that the formation of a RbPbI3 phase does not significantly affect the charge carrier lifetimes and consequently the performance of the devices. This brings new physical insights onto the role of different impurities in perovskite solar cells, which make these materials so remarkable., US Department of Energy, Office of Science, Office of Basic Energy Sciences (award no. DE-SC0001088)

Perovskite solar cells (PSCs) are currently one of the most promising photovoltaic technologies for highly efficient and cost-effective solar energy production. In only a few years, an unprecedented progression of preparation procedures and material compositions delivered lab-scale devices that have now reached record power conversion efficiencies (PCEs) higher than 20%, competing with most established solar cell materials such as silicon, CIGS, and CdTe. However, despite a large number of researchers currently involved in this topic, only a few groups in the world can reproduce >20% efficiencies on a regular n-i-p architecture. In this work, we present detailed protocols for preparing PSCs in regular (n-i-p) and inverted (p-i-n) architectures with >= 20% PCE. We aim to provide a comprehensive, reproducible description of our device fabrication , protocols. We encourage the practice of reporting detailed and transparent protocols that can be more easily reproduced by other laboratories. A better reporting standard may, in turn, accelerate the development of perovskite solar cells and related research fields.

Despite the fact that perovskite solar cells (PSCs) have a strong potential as a next-generation photovoltaic technology due to continuous efficiency improvements and the tunable properties, some important obstacles remain before industrialization is feasible. For example, the selection of low-cost or easy-to-prepare materials is essential for back-contacts and hole-transporting layers. Likewise, the choice of conductive substrates, the identification of large-scale manufacturing techniques as well as the development of appropriate aging protocols are key objectives currently under investigation by the international scientific community. This Review analyses the above aspects and highlights the critical points that currently limit the industrial production of PSCs and what strategies are emerging to make these solar cells the leaders in the photovoltaic field.

The focus of this work is the experimental investigation of soot formation in coflow flames formed of two fatty acid methyl esters (FAMEs) by employing the light extinction/scattering technique. Three different sets of experiments were conducted in this study. In the first set, radial soot volume fraction ( f v ) profiles of flames of vaporized neat canola methyl ester (B100CME) and neat soy methyl ester (B100SME) fuels both using air as the oxidizer were obtained. In the second set of experiments, the effect of oxygen content in the oxidizer stream on soot formation was studied in both FAME formed flames by increasing the oxygen content in the oxidizer stream from 21% to 35%, 50% and 80%. In the third set of experiments, the effect of fuel blending on the formation of soot particulates was studied in flames formed using CME blended with No. 2 diesel. The blends consisted of 80% biodiesel/20% diesel (B80) and 50% biodiesel/50% diesel (B50). The flames were scanned in the radial direction at various heights above the burner (HAB). For the B100CME-air flame the measured soot volume fraction f v peak was 4.04 ppm and was located at the symmetry axis at a HAB of 16.25 mm. For B100SME-air, the f v peak was measured to be 4.22 ppm at approximately the same flame height as in the CME-air flame. For the B100CME oxygen enriched-air flames the peak values at 35%, 50% and 80% were 6.50, 5.82 and 3.22 ppm, respectively. It was observed that by increasing the oxygen content in the B100CME flame from 21% to 35% oxygen, the f v peak increases by approximately 61%. However, a further increase in oxygen content in the oxidizer stream suppressed soot formation. A similar trend in the f v was observed for B100SME oxygen-enhanced flames. Furthermore, the increase of diesel fuel in the blending of B50CME resulted in significantly higher f v values compared to the B80CME. The addition of oxygen content in the oxidizer stream in these blended fuel flames (from air to 35%) resulted in an increase in the f v peak of approximately 47% and 71%, respectively. Centerline temperatures were measured at various HAB for selected flames.

The relationship between charge-carrier lifetime and the tolerance of lead halide perovskite (LHP) solar cells to intrinsic point defects has drawn much attention by helping to explain rapid improvements in device efficiencies. However, little is known about how charge-carrier lifetime and solar cell performance in LHPs are affected by extrinsic defects (i.e., impurities), including those that are common in manufacturing environments and known to introduce deep levels in other semiconductors. Here, we evaluate the tolerance of LHP solar cells to iron introduced via intentional contamination of the feedstock and examine the root causes of the resulting efficiency losses. We find that comparable efficiency losses occur in LHPs at feedstock iron concentrations approximately 100 times higher than those in p-type silicon devices. Photoluminescence measurements correlate iron concentration with nonradiative recombination, which we attribute to the presence of deep-level iron interstitials, as calculated from first-principles, as well as iron-rich particles detected by synchrotron-based X-ray fluorescence microscopy. At moderate contamination levels, we witness prominent recovery of device efficiencies to near-baseline values after biasing at 1.4 V for 60 s in the dark. We theorize that this temporary effect arises from improved charge-carrier collection enhanced by electric fields strengthened from ion migration toward interfaces. Our results demonstrate that extrinsic defect tolerance contributes to high efficiencies in LHP solar cells, which inspires further investigation into potential large-scale manufacturing cost savings as well as the degree of overlap between intrinsic and extrinsic defect tolerance in LHPs and "perovskite-inspired" lead-free stable alternatives.

The root cause of light- and elevated temperature-induced degradation (LeTID) in multicrystalline silicon p-type passivated emitter and rear cell (PERC) devices is still unknown. Some researchers hypothesize that high temperature firing processes dissolve metal-rich precipitates which can then participate in LeTID. To address this hypothesis, synchrotron-based X-ray techniques, including fluorescence and absorption near-edge spectroscopy, are employed. In as-grown industrial material, we observe collocated copper- and nickel-rich precipitates, which persist after firing and are below the detection limit after phosphorous diffusion. We conclude that precipitates decrease in size due to the firing process and that this may result in an increase in bulk interstitial metal concentration. We further employ microphotoluminescence at a grain versus grain boundary to highlight similarities and possible differences in degradation and regeneration behavior.

Antimony-doped tin oxide (ATO) aerogels have been prepared as conductive scaffolds for TiO2 in dye-sensitized solar cells (DSCs). The high surface area, porosity and particle interconnectivity inherent to aerogels, and the conductivity and transparency of ATO make these structures attractive as porous electron collectors. Aerogels were prepared by sol–gel processing and supercritical drying of ATO containing varying amounts of Sb. These were coated with varying TiO2 layer thicknesses by atomic layer deposition, sensitized with an organic dye (D149), and made into DSC devices using iodide/triiodide (I–/I3–) and ferrocene/ferrocenium (Fc/Fc+) electrolytes. Scanning electron microscopy was used to study the morphological characteristics of the aerogel materials. The effect of ALD cycles on the dye adsorption was measured. Current–voltage characteristics were used to study device performance. We found that ATO aerogels with 15% Sb have improved performance over TiO2 and undoped tin oxide aerogel devices. DSC ...

The brown alga Dictyota kunthii is one of the dominant species in the coastal areas of northern Chile affected by copper enrichment due to accumulated mining wastes. To assess its physiological plasticity in handling copper-mediated oxidative stress, 4-days copper exposure (ca. 100 μg/L) experiments were conducted with individuals from a copper impacted area and compared with the responses of plants from a non-impacted site. Several biochemical parameters were then evaluated and compared between populations. Results showed that individuals from the copper-impacted population normally displayed higher levels of copper content and antioxidant enzymes activity (catalase (CAT), ascorbate peroxidase (AP), dehydroascorbate reductase (DHAR), glutathione peroxidase (GP) and peroxiredoxins (PRX)). After copper exposure, antioxidant enzyme activity increased significantly in plants from the two selected sites. In addition, we found that copper-mediated oxidative stress was associated with a reduction of glutathione reductase (GR) activity. Moreover, metabolic profiling of extracellular metabolites from both populations showed a significant change after plants were exposed to copper excess in comparison with controls, strongly suggesting a copper-induced release of metabolites. The copper-binding capacity of those exudates was determined by anodic stripping voltammetry (ASV) and revealed an increased ligand capacity of the medium with plants exposed to copper excess. Results indicated that D. kunthii, regardless their origin, counteracts copper excess by various mechanisms, including metal accumulation, activation of CAT, AP, DHAR, GP and PRX, and an induced release of Cu binding compounds. Thus, plasticity in copper tolerance in D. kunthii seems constitutive, and the occurrence of a copper-tolerant ecotype seems unlikely.

The presence of organochlorine pesticides (OCPs) in biological and environmental samples has been studied for decades in many countries. Nonetheless, studies in Latin American countries like Colombia have been scarce. Determining the presence of OCPs in breast milk will be of relevance to assess exposures, potential health risks, and for surveillance among Latin American populations. Thirty-two breast-feeding mothers were selected to voluntarily participate in the study. Breast milk samples were analyzed for 10 OCPs (α-, β-, γ-, δ-HCH, Heptachlor, α-, γ-Chlordane, 4,4' DDT, 4,4' DDE, 4,4' DDD). Milk samples were analyzed using liquid-liquid extraction, followed by sulfuric acid clean-up, and quantified using GC/μECD. Results were confirmed by GC/MS. OCPs concentrations were normalized using fat content. In all but one sample, 4,4' DDE was quantified in concentrations ranging between17 and 14948 ng g(-1) (ng of OCP per g of lipids), with a mean value of 203 ng g(-1). One woman had 4,4' DDE concentrations that were orders of magnitude above the average concentrations observed worldwide. Concentrations of 4,4' DDE in a second breast milk sample collected in a different time period of lactation from a sub-group of 13 women from the original participants, showed no statistically significant difference with the concentrations found in the first sample. Based on the results obtained from the Persistent Organic Pollutants Global Monitoring Plan report of 2009 of the Stockholm Convention, Colombia ranks fourth from bottom to top in terms of 4,4' DDE average concentrations.

Electron transport and recombination are the essential processes that determine the charge collection efficiency in dye-sensitized solar cells (DSSC). While nearly 100% of charges are collected in well-built ordinary DSSCs, this value can be sharply reduced by the use of redox couples other than iodide/triiodide due to fast electron recombination. To compensate, structures capable of fast electron transport are needed. Nanorod arrays that have this attribute tend to suffer from low surface area, resulting in low dye loading and reduced light harvesting. We have therefore developed a novel nanocomposite structure consisting of zinc oxide (ZnO) nanorods coated with titanium dioxide (TiO2) nanoparticles using an electrostatic layer-by-layer (LbL) deposition technique. The titanium dioxide nanoparticle coating can add an order of magnitude of surface area and is compatible with known high-performance dyes. This composite nanostructure has been designed to take advantage of the improved electron transport alon...

Lead halide perovskites have over the past few years attracted considerable interest as photo absorbers in PV applications with record efficiencies now reaching 22%. It has recently been found that not only the composition but also the precise stoichiometry is important for the device performance. Recent reports have, for example, demonstrated small amount of PbI2 in the perovskite films to be beneficial for the overall performance of both the standard perovskite, CH3NH3PbI3, as well as for the mixed perovskites (CH3NH3)x(CH(NH2)2)(1-x)PbBryI(3-y). In this work a broad range of characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photo electron spectroscopy (PES), transient absorption spectroscopy (TAS), UV-vis, electroluminescence (EL), photoluminescence (PL), and confocal PL mapping have been used to further understand the importance of remnant PbI2 in perovskite solar cells. Our best devices were over 18% efficient, and had in line with previous results a small amount of excess PbI2. For the PbI2-deficient samples, the photocurrent dropped, which could be attributed to accumulation of organic species at the grain boundaries, low charge carrier mobility, and decreased electron injection into the TiO2. The PbI2-deficient compositions did, however, also have advantages. The record Voc was as high as 1.20 V and was found in PbI2-deficient samples. This was correlated with high crystal quality, longer charge carrier lifetimes, and high PL yields and was rationalized as a consequence of the dynamics of the perovskite formation. We further found the ion migration to be obstructed in the PbI2-deficient samples, which decreased the JV hysteresis and increased the photostability. PbI2-deficient synthesis conditions can thus be used to deposit perovskites with excellent crystal quality but with the downside of grain boundaries enriched in organic species, which act as a barrier toward current transport. Exploring ways to tune the synthesis conditions to give the high crystal quality obtained under PbI2-poor condition while maintaining the favorable grain boundary characteristics obtained under PbI2-rich conditions would thus be a strategy toward more efficiency devices.

We propose a novel tandem architecture design in which both top and bottom cells contain perovskite absorbers., Organic–inorganic perovskite structures in which lead is substituted by tin are exceptional candidates for broadband light absorption. Herein we present a thorough analysis of the optical properties of CH3NH3SnxPb1–xI3 films, providing the field with definitive insights about the possibilities of these materials for perovskite solar cells of superior efficiency. We report a user's guide based on the first set of optical constants obtained for a series of tin/lead perovskite films, which was only possible to measure due to the preparation of optical quality thin layers. According to the Shockley–Queisser theory, CH3NH3SnxPb1–xI3 compounds promise a substantial enhancement of both short circuit photocurrent and power conversion efficiency in single junction solar cells. Moreover, we propose a novel tandem architecture design in which both top and bottom cells are made of perovskite absorbers. Our calculations indicate that such perovskite-on-perovskite tandem devices could reach efficiencies over 35%. Our analysis serves to establish the first roadmap for this type of cells based on actual optical characterization data. We foresee that this study will encourage the research on novel near-infrared perovskite materials for photovoltaic applications, which may have implications in the rapidly emerging field of tandem devices.