“Caracterización de los sistemas de producción de ovinos de pelo en el suroeste del departamento de Matagalpa 2010”

Con el objetivo de caracterizar los sistemas de producción de ovinos de pelo en el territorio suroeste del departamento de Matagalpa 2010. (Sébaco, Ciudad Darío, San Isidro y Matagalpa). Se aplicó una encuesta a 103 productores que poseen ovinos de pelo, la muestra se definió aleatoriamente utilizando la ecuación planteada por Scheaffer (1987), se utilizó la técnica de muestreo de bola de nieve, planteada por Frey et al (2000). Esta investigación permitió conocer las debilidades y oportunidades en los sistemas de explotación de esta especie promisoria para la zona seca del país. Con los resultados obtenidos de las encuestas se procedió ha elaborar una base de datos en el programa SPSS versión 11.5 en español. Encontrando un predominio del sexo femenino como titulares de las explotaciones ovinas, 58.3% cursó educación primaria, el 98% de las explotaciones cuentan con raza pelibuey, el 100% de las explotaciones realizan destete y monta de forma natural, una media de mortalidad de corderos de 1, alimentan a las ovejas con potrero sin división (81.6%), se suministra pasto de corte, pastoreo, leguminosas y se suplementa sal común 49.5%, aplican vacunas contra ántrax y pierna negra (63.1%), desparasitaciones internas y externas (66%), ambos con una frecuencia de 2 veces al año, en el manejo productivo no se lleva control en la actividad ovina (100%), los equipo e instalaciones son rústicas, los corrales ovinos el son elaborados con alambre y/o madera, techado con plástico y/o zinc (49.51%), en cuanto a asistencia técnica el 58.3% ha recibid

Possibility of NCS Group Anchor for Ru Dye Adsorption to Anatase TiO₂(101) Surface: A Density Functional Theory Investigation

We examined the possibility of the presence of isothiocyanate (NCS) group anchor for Ru dye adsorption to anatase TiO₂(101) surface in typical dye-sensitized solar cells (DSCs), motivated by the recent X-ray photoelectron spectroscopy (XPS) experimental observations of the NCS anchors. A variety of adsorption configurations were examined with model molecules of CH₃NCS by density functional theory (DFT) calculations. To compare with the experimental XPS spectra, we also calculated core–electron binding energies using (TiO₂)₃₈ cluster model. We demonstrated that 0.6–0.7 eV of the observed chemical shift in the S 2p XPS spectra can be assigned to the S interactions with the surface Ti atom and O vacancy, while 8.8 eV shift in the S 1s level is connected to the S–Ti vacancy interaction. On the other hand, it is also confirmed that the adsorption energies of COOH group and acetonitrile solvent molecule are usually larger than that for the NCS group. Therefore, the Ru dye adsorption through the NCS anchor is less probable even on the surface in vacuum and further decreases in the solution environment. With these results, we conclude that the NCS group anchoring is possible in the vacuum environment as shown by the XPS studies, while it will be negligible on the working electrode of the solar cell

Termination Dependence of Tetragonal CH₃NH₃PbI₃ Surfaces for Perovskite Solar Cells

We investigated the termination dependence of structural stability and electronic states of the representative (110), (001), (100), and (101) surfaces of tetragonal CH₃NH₃PbI₃ (MAPbI₃), the main component of a perovskite solar cell (PSC), by density functional theory calculations. By examining various types of PbI_<i>x</i> polyhedron terminations, we found that a vacant termination is more stable than flat termination on all of the surfaces, under thermodynamic equilibrium conditions of bulk MAPbI₃. More interestingly, both terminations can coexist especially on the more probable (110) and (001) surfaces. The electronic structures of the stable vacant and PbI₂-rich flat terminations on these two surfaces largely maintain the characteristics of bulk MAPbI₃ without midgap states. Thus, these surfaces can contribute to the long carrier lifetime actually observed for the PSCs. Furthermore, the shallow surface states on the (110) and (001) flat terminations can be efficient intermediates of hole transfer. Consequently, the formation of the flat terminations under the PbI₂-rich condition will be beneficial for the improvement of PSC performance

First-Principles Study of Electron Injection and Defects at the TiO₂/CH₃NH₃PbI₃ Interface of Perovskite Solar Cells

We investigated electron injection rates and vacancy defect properties by performing first-principles calculations on the interface of an anatase-TiO₂(001) and a tetragonal CH₃NH₃PbI₃(110) (MAPbI₃(110)). We found that the coupling matrix element between the lowest unoccupied molecular orbital of MAPbI₃ and the TiO₂ conduction band (CB) minimum is negligibly small, the indication being that electron-injection times for low-energy excited states are quite long (more than several tens of picoseconds). We also found that higher-lying CB states coupled more strongly; injection was expected to take place on a femtosecond time scale. Furthermore, we found that vacancy defects in the TiO₂ layer produced undesired defect levels that caused hole traps and recombination centers. Whereas most of the vacancy defects in the MAPbI₃ layer produced no additional states in the MAPbI₃ gap, a Pb vacancy (V_Pb) at the interface created an energy level below the MAPbI₃ CB edge and had a lower energy of formation than the V_Pb defect in bulk because of the interaction with the TiO₂ surface

Space–Charge Layer Effect at Interface between Oxide Cathode and Sulfide Electrolyte in All-Solid-State Lithium-Ion Battery

We theoretically elucidated the characteristics of the space–charge layer (SCL) at interfaces between oxide cathode and sulfide electrolyte in all-solid-state lithium-ion batteries (ASS-LIBs) and the effect of the buffer layer interposition, for the first time, via the calculations with density functional theory (DFT) + U framework. As a most representative system, we examined the interfaces between LiCoO₂ cathode and β-Li₃PS₄ solid electrolyte (LCO/LPS), and the LiCoO₂/LiNbO₃/β-Li₃PS₄ (LCO/LNO/LPS) interfaces with the LiNbO₃ buffer layers. The DFT+U calculations, coupling with a systematic procedure for interface matching, showed the stable structures and the electronic states of the interfaces. The LCO/LPS interface has attractive Li adsorption sites and rather disordered structure, whereas the interposition of the LNO buffer layers forms smooth interfaces without Li adsorption sites for both LCO and LPS sides. The calculated energies of the Li-vacancy formation and the Li migration reveal that subsurface Li in the LPS side can begin to transfer at the under-voltage condition in the LCO/LPS interface, which suggests the SCL growth at the beginning of charging, leading to the interfacial resistance. The LNO interposition suppresses this growth of SCL and provides smooth Li transport paths free from the possible bottlenecks. These aspects on the atomic scale will give a useful perspective for the further improvement of the ASS-LIB performance

Panchromatic Donor–Acceptor–Donor Conjugated Oligomers for Dye-Sensitized Solar Cell Applications

We report on a sexithienyl and two donor–acceptor−donor oligothiophenes, employing benzothiadiazole and isoindigo as electron-acceptors, each functionalized with a phosphonic acid group for anchoring onto TiO₂ substrates as light-harvesting molecules for dye sensitized solar cells (DSSCs). These dyes absorb light to wavelengths as long as 700 nm, as their optical HOMO/LUMO energy gaps are reduced from 2.40 to 1.77 eV with increasing acceptor strength. The oligomers were adsorbed onto mesoporous TiO₂ films on fluorine doped tin oxide (FTO)/glass substrates and incorporated into DSSCs, which show AM1.5 power conversion efficiencies (PCEs) ranging between 2.6% and 6.4%. This work demonstrates that the donor–acceptor–donor (D-A-D) molecular structures coupled to phosphonic acid anchoring groups, which have not been used in DSSCs, can lead to high PCEs

Acetonitrile Solution Effect on Ru N749 Dye Adsorption and Excitation at TiO₂ Anatase Interface

We investigated stable structures and photoexcitation character of Ru N749 dye (black dye (BD)) adsorption to TiO₂ anatase (101) interface immersed in bulk acetonitrile (AN) solution, a most representative electrode interface in dye-sensitized solar cells (DSCs). Density-functional-theory-based molecular dynamics (DFT-MD) with explicit solvent molecules was used to take into account the fluctuations of solvation shells and adsorbed molecules. We demonstrated that BD adsorption via deprotonated carboxylate two anchors (d2) is the most stable at the interface, while the one protonated carboxyl anchor (p1) has the average energy only slightly higher than the d2. This indicates that the p1 state can still coexist with the d2 under equilibrium. It is in contrast with the calculated large stability of the p1 in vacuo. Inhomogeneous charge distribution and anchor fluctuation enhanced by AN solution causes this d2 stabilization. The calculated projected densities of states and the photoabsorption spectra clearly show that the d2 state has larger driving force of the electron injection into the TiO₂, whereas the photoabsorption in the wavelength region over 800 nm, a characteristic of BD sensitizer, is mainly attributed to the p1 state even in the AN solution. Consequently, the better performance of BD DSC can be understood in terms of the cosensitizer framework of the d2 and p1 states

Constructing High-Efficiency D–A−π–A-Featured Solar Cell Sensitizers: a Promising Building Block of 2,3-Diphenylquinoxaline for Antiaggregation and Photostability

Controlling the sensitizer morphology on a nanocrystalline TiO₂ surface is beneficial to facilitating electron injection and suppressing charge recombination. Given that the grafted alkyl chain on a π-bridge thiophene segment for preventing π aggregation can deteriorate its intrinsic photostability, we incorporate a promising building block of 2,3-diphenylquinoxaline as the additional acceptor to construct a novel D–A−π–A-featured dye <b>IQ</b>_<b>4</b>, which exhibits several characteristics: (i) efficiently decreasing the molecular HOMO–LUMO energy gap by extending its absorption bands; (ii) showing a moderate electron-withdrawing capability for an ideal balance in both promising photocurrent and photovoltage; (iii) endowing an ideal morphology control with strong capability of restraining the intermolecular aggregation and facilitating the formation of a compact sensitizer layer via two twisted phenyl groups grafted onto the quinoxaline unit. The coadsorbent-free dye-sensitized solar cell (DSSC) based on dye <b>IQ</b>_<b>4</b> exhibits very promising conversion efficiency as high as 9.24 ± 0.05%, with a short-circuit current density (<i>J</i>_sc) of 17.55 mA cm^–2, an open-circuit voltage (<i>V</i>_oc) of 0.74 V, and a fill factor (FF) of 0.71 under AM 1.5 illumination (100 mW cm^–2). <b>IQ</b>_<b>4</b>-based DSSC devices with an ionic liquid electrolyte can keep constant performance during a 1000 h aging test under 1 sun at 60 °C. Because of spatial restriction, the two phenyl groups grafted onto the additional electron-withdrawing quinoxaline are demonstrated as efficient building blocks, not only improving its photostability and thermal stability but also allowing it to be a successful antiaggregation functional unit. As a consequence, the incorporated 2,3-diphenylquinoxaline unit can realize a facile structural modification for constructing organic coadsorbent-free D–A−π–A-featured sensitizers, thus paving a way to replace the common, stability-deleterious grafted alkyl chain on the thienyl bridge

Consecutive Morphology Controlling Operations for Highly Reproducible Mesostructured Perovskite Solar Cells

Perovskite solar cells have shown high photovoltaic performance but suffer from low reproducibility, which is mainly caused by low uniformity of the active perovskite layer in the devices. The nonuniform perovskites further limit the fabrication of large size solar cells. In this work, we control the morphology of CH₃NH₃PbI₃ on a mesoporous TiO₂ substrate by employing consecutive antisolvent dripping and solvent-vapor fumigation during spin coating of the precursor solution. The solvent-vapor treatment is found to enhance the perovskite pore filling and increase the uniformity of CH₃NH₃PbI₃ in the porous scaffold layer but slightly decrease the uniformity of the perovskite capping layer. An additional antisolvent dripping is employed to recover the uniform perovskite capping layer. Such consecutive morphology controlling operations lead to highly uniform perovskite in both porous and capping layers. By using the optimized perovskite deposition procedure, the reproducibility of mesostructured solar cells was greatly improved such that a total of 40 devices showed an average efficiency of 15.3% with a very small standard deviation of 0.32. Moreover, a high efficiency of 14.9% was achieved on a large-size cell with a working area of 1.02 cm²

Tuning the Photovoltaic Performance of Benzocarbazole-Based Sensitizers for Dye-Sensitized Solar Cells: A Joint Experimental and Theoretical Study of the Influence of π‑Spacers

Tuning the parameters to enhance the efficiencies of a novel set of metal free sensitizers for dye sensitized solar cells (DSSC) is carried out by varying the π-conjugated spacers that link the donor benzocarbazole to the acceptor cyanoacrylic acid. The molecules are synthesized by different combinations of spacers, namely fluorene-thiophene (BFT), fluorene-furan (BFF), fluorene-phenyl (BFB), and thiophene-phenyl (BTB). The molar extinction coefficients of all the dyes are high which is attributed to benzocarbazole, but it is higher in the dyes in which fluorene is one of the spacers. But interestingly, in the photovoltaic device when the non-fluorene dye BTB is the sensitizer, red-shifted and broader incident photon-to-current efficiency (IPCE) curves are obtained leading to larger short circuit current density, <i>J</i>_sc, almost double when compared to BFB-based cell. The efficiency of the device with this dye as the sensitizer is also the highest in this series. The reasons behind these observations are investigated using computational techniques