The performance of organometallic perovskite solar cells has rapidly surpassed those of both traditional dye-sensitized and organic photovoltaics, e.g. solar cells based on CH3NH3PbI3 have recently reached 18% conversion efficiency. We analyze its electronic structure and optical properties within the quasiparticle self-consistent GW approximation (QSGW ). Quasiparticle self-consistency is essential for an accurate description of the band structure: bandgaps are much larger than what is predicted by the local density approximation (LDA) or GW based on the LDA. Several characteristics combine to make the electronic structure of this material unusual. First, there is a strong driving force for ferroelectricity, as a consequence the polar organic moiety CH3NH3. The moiety is only weakly coupled to the PbI3 cage; thus it can rotate give rise to ferroelectric domains. This in turn will result in internal junctions that may aid separation of photoexcited electron and hole pairs, and may contribute to the current-voltage hysteresis found in perovskite solar cells. Second, spin orbit modifies both valence band and conduction band dispersions in a very unusual manner: both get split at the R point into two extrema nearby. This can be interpreted in terms of a large Dresselhaus term, which vanishes at R but for small excursions about R varies linearly in k. Conduction bands (Pb 6p character) and valence bands (I 5p) are affected differently; moreover the splittings vary with the orientation of the moiety. We will show how the splittings, and their dependence on the orientation of the moiety through the ferroelectric effect, have important consequences for both electronic transport and the optical properties of this material.

http://absimage.aps.org/image/MAR15/MWS_MAR15-2014-020499.pdf

Electronic structure of hybrid halide perovskite photovoltaic absorbers

Despite tremendous recent efforts, noninvasive sweat monitoring is still far from delivering its early analytical promise. Here, we describe a flexible epidermal microfluidic detection platform fabricated through hybridization of lithographic and screen-printed technologies, for efficient and fast sweat sampling and continuous, real-time electrochemical monitoring of glucose and lactate levels. This soft, skin-mounted device judiciously merges lab-on-a-chip and electrochemical detection technologies, integrated with a miniaturized flexible electronic board for real-time wireless data transmission to a mobile device. Modeling of the device design and sweat flow conditions allowed optimization of the sampling process and the microchannel layout for achieving attractive fluid dynamics and rapid filling of the detection reservoir (within 8 min from starting exercise). The wearable microdevice thus enabled efficient natural sweat pumping to the electrochemical detection chamber containing the enzyme-modified e...

Epidermal Microfluidic Electrochemical Detection System: Enhanced Sweat Sampling and Metabolite Detection

Electrochemistry, biosensors and microfluidics are popular research topics that have attracted widespread attention from chemists, biologists, physicists, and engineers. Here, we introduce the basic concepts and recent histories of electrochemistry, biosensors, and microfluidics, and describe how they are combining to form new application-areas, including so-called “point-of-care” systems in which measurements traditionally performed in a laboratory are moved into the field. We propose that this review can serve both as a useful starting-point for researchers who are new to these topics, as well as being a compendium of the current state-of-the art for experts in these evolving areas.

Electrochemistry, biosensors and microfluidics: a convergence of fields

Modified electrodes used for electrochemical detection of metal ions in environmental analysis.

Flexible perovskite solar cells have attracted widespread research effort because of their potential in portable electronics. The efficiency has exceeded 18 % owing to the high-quality perovskite film achieved by various low-temperature fabrication methods and matching of the interface and electrode materials. This Review focuses on recent progress in flexible perovskite solar cells concerning low-temperature fabrication methods to improve the properties of perovskite films, such as full coverage, uniform morphology, and good crystallinity; demonstrated interface layers used in flexible perovskite solar cells, considering key figures-of-merit such as high transmittance, high carrier mobility, suitable band gap, and easy fabrication via low-temperature methods; flexible transparent electrode materials developed to enhance the mechanical stability of the devices; mechanical and long-term environmental stability; an outlook of flexible perovskite solar cells in portable electronic devices; and perspectives of commercialization for flexible perovskite solar cells based on cost.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/anie.201809781

Recent Advances in Flexible Perovskite Solar Cells: Fabrication and Applications

Liquid exfoliation of three-dimensional bulk solids with an inherent layered structure is an effective and scalable method to produce stable re-aggregation colloidal inks of 2D materials that are suitable for solution processing. Shear mixing is a relatively gentle technique that allows exfoliation while preserving the native lateral size of the 3D precursors, while tip sonication often leads to extensive structural damage, producing 2D sheets where many edge defects are introduced. We present a mixed approach to obtain liquid dispersions of few-layer graphene flakes, wherein the average lateral size of the colloids can be tuned in a controlled way. This strategy relies on the application of defined tip sonication steps on graphene inks previously prepared through the use of a shear mixer, thus starting with already-exfoliated micro-sheets with a limited amount of edge defects. Our approach could represent a valuable method to prepare 2D material inks with variable size distributions, as differences in this parameter could have a significant impact on the electronic behavior of the final material and thus on its field of application.

https://www.mdpi.com/2073-4352/10/11/1049/pdf

Controlled Size Reduction of Liquid Exfoliated Graphene Micro-Sheets via Tip Sonication

We developed a simple methodology for a direct control of the height of carboxylated single-walled carbon nanotube (SWNT) forests. We found that the important step is a good control of the oxidation temperature of the nanotubes. SWNTs oxidation at different temperature was followed by Raman and X-ray photoelectron spectroscopies. Atomic force microscopy images showed that micropatterned self-assembled monolayers forests have average height from 20 to 80 nm using SWNTs oxidized in the temperature ranging from 323 to 303 K, respectively.

Nanotubes oxidation temperature controls the height of single-walled carbon nanotube forests on gold micropatterned thin layers

This review was devoted to outlining the use and potential increasing application of the Design of Experiment (DoE) approach to the rational and planned synthesis of inorganic nanomaterials, with a particular focus on polycrystalline nanostructures (metal and alloys, oxides, chalcogenides, halogenides, etc.) produced by sustainable wet chemistry routes based on a multi-parameter experimental landscape. After having contextualised the stringent need for a rational approach to inorganic materials’ synthesis, a concise theoretical background on DoE is provided, focusing on its statistical basis, shortly describing the different sub-methodologies, and outlining the pros and cons of each. In the second part of the review, a wider section is dedicated to the application of DoE to the rational synthesis of different kinds of chemical systems, with a specific focus on inorganic materials.

/pdf/design-of-experiment-a-rational-and-still-unexplored-1rt9wrld.pdf

Design of Experiment: A Rational and Still Unexplored Approach to Inorganic Materials’ Synthesis

2D materials are interesting flat nanoplatforms for the implementation of different electrochemical processes, due to the high surface area and tunable electronic properties. 2D transition metal dichalcogenides (TMDs) can be produced through convenient top-down liquid-phase exfoliation (LPE) methods and present capacitive behaviour that can be exploited for energy storage applications. However, in their thermodynamically stable 2H crystalline phase, they present poor electrical conductivity, being this phase a purely semiconducting one. Combination with conducting polymers like polyaniline (PANI), into nanohybrids, can provide better properties for the scope. In this work, we report on the preparation of 2D WS2@PANI hybrid materials in which we exploit the LPE TMD nanoflakes as scaffolds, onto which induce the in-situ aniline polymerization and thus achieve porous architectures, with the help of surfactants and sodium chloride acting as templating agents. We characterize these species for their capacitive behaviour in neutral pH, achieving maximum specific capacitance of 160 F/g at a current density of 1 A/g, demonstrating the attractiveness of similar nanohybrids for future use in low-cost, easy-to-make supercapacitor devices.

/pdf/nanostructured-2d-ws2-pani-nanohybrids-for-electrochemical-171u09sw.pdf

Nanostructured 2D WS2@PANI nanohybrids for electrochemical energy storage

The nanobioelectrochemistry is a new interdisciplinary field which aims to combine the purposes of bionanotechnology with electrochemistry methodology. It focuses on the study of the electron transfer (ET) kinetics that occur at biointerfaces during redox reactions Chen et al. (2007). The ET results in a electron current that can be easily quantified allowing accurate and high sensitive measurements. These properties are extremely relevant on biological field in which the lacking of quantitative measurement is often a bottle neck in developing new processes. The majority of biosensors is based on one or more bioactive molecules used in conjunction with an electrode. A redox reaction could be detected electrochemically by three different measurements: i) direct redox of a molecule involved in biological environments; ii) redox of a small mediator species that shuttles between the bioactive molecule and the electrode; iii) direct ET between the biomolecule redox site and the electrode (Fig. 1). Bioactive molecules are referred as such enzymes that require cofactors (as FAD or NADH) for catalytic activity. These bioactive molecules ensure high specificity due to structure recognition between enzymatic protein and substrate and high sensitivity due to high redox catalytic efficiency of cofactors. This latter mechanism of bioelectrochemical sensor is less common because it requires an intimate coupling between electrodes and biomolecules preserving their biological activity. On the other hand, direct electron transfer mechanism has intrinsic advantages with respect to the other two mechanisms because the electrochemical signal can be quantitatively related to a biological phenomenon without signal dissipation generated by the additional mediator. It is well known that the mediator can either react on the electrode or diffuse away in the bulk solution leading to a general sensitivity lowering. In this context, achieving direct ET could not be straightfarward and for this reason, modification of biomolecules or electrode surfaces through the use of novel nanostructured materials as mediator and the engineering of biointerfaces has been reported Hartmann (2005); Hernandez-Santos et al. (2002); Kohli et al. (2004); Wang (2005). The integration at nanoscale length is of paramount importance for reducing the probability of mediator charge dissipation at the interface towards the bulk. The new interface realized comprehending the system nanostructure/biomolecule can be defined as the nanostructured biointerface. 11

/pdf/electrochemical-biosensing-with-carbon-nanotubes-14prspkb9a.pdf

Francesco Lamberti

Papers

Controlled Size Reduction of Liquid Exfoliated Graphene Micro-Sheets via Tip Sonication

Nanotubes oxidation temperature controls the height of single-walled carbon nanotube forests on gold micropatterned thin layers

Design of Experiment: A Rational and Still Unexplored Approach to Inorganic Materials’ Synthesis

Nanostructured 2D WS2@PANI nanohybrids for electrochemical energy storage

Electrochemical Biosensing with Carbon Nanotubes