Hybrid heterojunctions of solution-processed semiconducting 2d transition metal dichalcogenides

Exfoliated transition metal dichalcogenides (2D-TMDs) are attractive light-harvesting materials for large-area and inexpensive solar energy conversion given their ability to form highly tolerant heterojunctions. However, the preparation of large-area heterojunctions with these materials remains a challenge toward practical devices, and the details of photogenerated charge carrier harvesting are not well established. In this work, we use all solution-based methods to prepare large-area hybrid heterojunction films consisting of exfoliated semiconducting 2H-MoS2 flakes and a perylene-diimide (PDI) derivative. Hybrid photoelectrodes exhibited a 6-fold improvement in photocurrent compared to that of bare MoS2 or PDI films. Kelvin probe force microscopy, X-ray photoelectron spectroscopy, and transient absorption measurements of the hybrid films indicate the formation of an interfacial dipole at the MoS2/organic interface and suggest that the photogenerated holes transfer from MoS2 to the PDI. Moreover, performing the same analysis on MoSe2-based hybrid devices confirms the importance of proper valence band alignment for efficient charge transfer and photogenerated carrier collection in TMD/organic semiconductor hybrid heterojunctions

In Situ Electrochemical Oxidation of Cu2S into CuO Nanowires as a Durable and Efficient Electrocatalyst for Oxygen Evolution Reaction

Development of cost-effective oxygen evolution catalysts is of capital importance for the deployment of large-scale energy-storage systems based on metal-air batteries and reversible fuel cells. In this direction, a wide range of materials have been explored, especially under more favorable alkaline conditions, and several metal chalcogenides have particularly demonstrated excellent performances. However, chalcogenides are thermodynamically less stable than the corresponding oxides and hydroxides under oxidizing potentials in alkaline media. Although this instability in some cases has prevented the application of chalcogenides as oxygen evolution catalysts and it has been disregarded in some others, we propose to use it in our favor to produce high-performance oxygen evolution catalysts. We characterize here the in situ chemical, structural, and morphological transformation during the oxygen evolution reaction (OER) in alkaline media of CuS into CuO nanowires, mediating the intermediate formation of Cu(OH). We also test their OER activity and stability under OER operation in alkaline media and compare them with the OER performance of Cu(OH) and CuO nanostructures directly grown on the surface of a copper mesh. We demonstrate here that CuO produced from in situ electrochemical oxidation of CuS displays an extraordinary electrocatalytic performance toward OER, well above that of CuO and Cu(OH) synthesized without this transformation

Engineering the self-assembly of diketopyrrolopyrrole-based molecular semiconductors via an aliphatic linker strategy

The solid-state self-assembly of molecular semiconductors is a key aspect for controlling the optoelectronic properties of organic electronic materials. Herein, we investigate the use of a flexible linker strategy to control the self-assembly of a solution-processable diketopyrrolopyrrole semiconductor coded as DPP(TBFu)(2). Two distinct dimers-prepared with varied linker position relative to the orientation of the conjugated core-reveal the effect of connectivity on the solid-state self-assembly and optoelectronic properties-favoring either Hor J-type aggregation. The dimer with a "vertical"linker orientation exhibits a poor crystallinity in neat films, but improves hole mobility in OFETs 10-fold, reaching 3.0 x 10(-3) cm(2) V-1 s(-1) when used as an additive with DPP(TBFu)(2). Distinctively, the dimer with a "horizontal" linking orientation does not enhance charge carrier transport, but is found to affect the thermal stability of donor : acceptor blends in OPVs with PCBM. Devices retain 90% of their initial conversion efficiency after 5 hours of thermal stress, compared to only 45% for control devices. Thermodynamic and kinetic rationales further suggest that this flexible linker strategy represents a powerful tool to control supramolecular assembly in molecular semiconductors without altering the nature of the core conjugated segment

A Gibeon meteorite yields a high-performance water oxidation electrocatalyst

Examining the electrocatalytic performance of naturally-occurring metallic minerals is of interest for energy conversion applications given their unique atomic composition and formation history. Herein, we report the electrocatalytic function of an iron-based Gibeon meteorite for the oxygen evolution reaction (OER). After ageing under operational conditions in an alkaline electrolyte, an activity matching or possibly slightly superior to the best performing OER catalysts emerges, with stable overpotentials as low as 270 mV (for 10 mA cm(-2)) and Tafel slopes of 37 mV decade(-1). The Faradaic efficiency for the OER was unity and no deterioration in performance was detected during 1000 hours of OER operation at 500 mA cm(-2). Mechanistic studies suggest an operando surface modification involving the formation of a 3D oxy(hydroxide) layer with a metal atom composition of Co0.11Fe0.33Ni0.55, as indicated by Raman and XPS studies and trace Ir as indicated via elemental analysis. The growth of the catalyst layer was self-limiting to <200 nm after ca. 300 hours of operation as indicated through XPS depth profiling and cyclic voltammetry. The unique composition and structure of the Gibeon meteorite suggest that further investigation of Ir-Co-Ni-Fe systems or other alloys inspired by natural materials for water oxidation are of interest

Surface modification of semiconductor photoelectrodes

International audienceAn overview of surface engineering approaches to enhance the photoelectrochemical performance of commmon semiconductor photoelectrodes for solar energy conversion

Análisis financiero: una herramienta clave para la toma de decisiones de gerencia

Financial analyzes are considered a fundamental piece to be able to detect the situation, as well as the economic and financial performance of any organization, through which difficulties can be detected and then the necessary corrections can be made. The objective that has been raised through this study is to analyze what is the degree of relevance that is given to financial analysis as a key instrument in management decision-making, which is why a bibliographic study is carried out by means of theoretical bases of several authors. A financial analysis or study is based on the calculations of financial indicators, which are expressed by efficiency, solvency, performance, liquidity, indebtedness, and the profitability of the entity, financial analyzes are based on concrete amounts due to inflation the same amount that is provided by true, current, financial and accurate information. It can be concluded by stating that financial analyzes are both analytical and key management tools for the activities carried out by every organization, which determine the financial situations, which it is going through, thus allowing to recognize what the future it will have will be.Los análisis financieros son considerados una pieza fundamental para poder detectar la situación, así como el desempeño tanto económico como el financiero que tiene toda organización, por medio del cual se podrán detectar las dificultades y luego poder realizar las correcciones necesarias. El objetivo que se ha planteado por medio de este estudio es el de analizar cuál es el grado de relevancia que se le da a los análisis financieros como un instrumento clave en la toma de decisiones de gerencia, es así que se realiza un estudio bibliográfico por medio de bases teóricas de varios autores. Un análisis o estudio financiero se llega a basar en el cálculo de los indicadores de las finanzas los mismos que son expresados por la eficiencia, solvencia, rendimiento, liquidez, endeudamiento, y la rentabilidad que posee la entidad, los análisis financieros se encuentran basados en cantidades concretas debido a la inflación la misma que se proporciona por la información veraz, actual, financiera y precisa. Se puede concluir expresando que los análisis financieros son herramientas tanto analíticas y gerenciales claves para las actividades que realiza toda organización las cuales determinan las situaciones financieras, por las que está pasando, permitiendo así reconocer cual será el futuro que tendrá la misma

Self-assembled 2D WSe2 thin films for photoelectrochemical hydrogen production

WSe2-a layered semiconductor that can be exfoliated into atomically thin two-dimensional sheets-offers promising characteristics for application in solar energy conversion. However, the lack of controllable, cost-effective methods to scalably fabricate homogeneous thin films currently limits practical application. Here we present a technique to prepare controlled thin films of 2D WSe2 from dispersions of solvent-exfoliated few-layer flakes. Flake self-assembly at a liquid/liquid interface (formed exceptionally from two non-solvents for WSe2) followed by substrate transfer affords large-area thin films with superior 2D flake alignment compared with traditional (liquid/air) self-assembly techniques. We further demonstrate, for the first time, solar-to-hydrogen conversion from solution-processed WSe2 thin films. Bare photoelectrodes with a thickness of ca. 25 nm exhibit sustained p-type photocurrent under simulated solar illumination, and up to 1.0 mA cm(-2) at 0 V versus reversible hydrogen electrode with an added water reduction catalyst (Pt). The importance of the self-assembled morphology is established by photoelectrochemical and conductivity measurements

Improving charge collection with delafossite photocathodes: a host–guest CuAlO2/CuFeO2 approach

p-Type delafossite CuFeO2 has recently been reported as a promising candidate for direct photoelectrochemical solar water reduction in alkaline conditions. However, despite its favorable optical band gap energy and light absorption, this material suffers from poor electron–hole separation that limits its optimum thickness to a few hundred nanometers. This limitation can be addressed by a host–guest strategy, where a mesoporous p-type scaffold is used to support a thin-film of the light absorber. Here we demonstrate this host–guest approach for the first time with CuFeO2 using p-type transparent CuAlO2 as a scaffold. Optimizing the scaffold layer thickness at 2 μm resulted in a 2.4-fold increase in photocurrent in the presence of O2—a sacrificial electron scavenger—reaching 2.4 mA cm−2 at +0.4 V vs. RHE. Moreover, comparing the performance to host–guest electrodes prepared with an insulating SiO2 scaffold as a control suggested that the observed improvement with CuAlO2 was due to a decreased recombination stemming from improved charge separation in addition to improved charge transport through the scaffold compared to the CuFeO2 film alone

Direct Light-Driven Water Oxidation by a Ladder-Type Conjugated Polymer Photoanode

A conjugated polymer known for high stability (poly[benzimidazobenzophenanthroline], coded as BBL) is examined as a photoanode for direct solar water oxidation. In aqueous electrolyte with a sacrificial hole acceptor (SO32-), photoelectrodes show a morphology-dependent performance. Films prepared by a dispersion-spray method with a nanostructured surface (feature size of similar to 20 nm) gave photocurrents up to 0.23 +/- 0.02 mA cm(-2) at 1.23 V-RHE under standard simulated solar illumination. Electrochemical impedance spectroscopy reveals a constant flat-band potential over a wide pH range at +0.31 V-NHE. The solar water oxidation photocurrent with bare BBL electrodes is found to increase with increasing pH, and no evidence of semiconductor oxidation was observed over a 30 min testing time. Characterization of the photo-oxidation reaction suggests H2O2 or center dot OH production with the bare film, while functionalization of the interface with 1 nm of TiO2 followed by a nickel-cobalt catalyst gave solar photocurrents of 20-30 mu A cm(-2), corresponding with 02 evolution. Limitations to photocurrent production are discussed

Autodecomposition Approach for the Low-Temperature Mesostructuring of Nanocrystal Semiconductor Electrodes

Templating nanocrystals into mesoporous electrodes using an organic porogen typically requires thermal oxidation at >400 degrees C to completely remove the organic material and afford good electronic properties. These oxidation conditions are incompatible with many NC materials. Here, we demonstrate that nitrocellulose can afford mesoporous CdS and CZTS nanocrystal thin film electrodes at only 250-300 degrees C in air or under argon. Remarkable control over the surface area and the average pore size (20-100 nm) in thin films are demonstrated by varying the ratio of preformed nanocrystals and nitrocellulose. Moreover the mesoporous electrodes exhibit excellent optoelectronic properties. Photoelectrochemical performance is enhanced due to the increased active surface area, showing an 8-fold photocurrent increase over compact nanocrystal films, and an IPCE over 70%