Curriculum and teaching: what and how student at risk are thought?

En el presente artículo se analiza el currículo y la enseñanza de dos programas o medidas que se desarrollan en la Región de Murcia y en la Comunidad de Andalucía –Programa de Diversificación Curricular y Programa de Iniciación Profesional y/o Programa de Garantía Social- ambos destinados al alumnado con serias dificultades para continuar la enseñanza en las aulas regulares. Tras presentar diversos datos recogidos a través de cuestionarios y entrevistas con diferentes sujetos implicados, se analizan y valoran los resultados de la investigación realizada, procurando responder a la cuestión de en que grado el currículo diseñado en tales programas y la formación y aprendizajes logrados han contribuido a responder a las necesidades de este alumnadoThe article analyses curriculum and teaching of two programs in the Region of Murcia and in the Community of Andalusia - Program of Diversification Curricular and Program of Professional Initiation and / or Program of Social Guarantee – designed and implemented with students at risks, in serious difficulties to progress their learning in regular classrooms and teaching. After presenting different data gathered throw questionnaires and interviews carried out with different teachers, the outcomes are analyzed and valued in order to answer the question related to the degree in which de curriculum designed and its implementation in such programs respond properly to students needs and contributed to theirs expected learnin

Spray-Pyrolyzed ZnO as Electron Selective Contact for Long-Term Stable Planar CH3NH3PbI3 Perovskite Solar Cells

Electron selective contacts (ESCs) play an important role in the performance of perovskite solar cells (PSCs). ZnO has attracted important attention as a good material for ESCs because of its matched energy levels with those of perovskite, its high transmittance in the visible region, and its high electron mobility. Here we reported the use of ZnO thin layers prepared by spray pyrolysis as ESC for PSCs. Our ZnO based planar CH3NH3PbI3 (MAPbI3) devices not only were stable in a humidity of 35% but also improved the performance even after more than 1 month of preparation, due to an increase of charge transfer at the ZnO interface as it has been characterized by impedance spectroscopy. The formation of ZnO depends on preparation conditions such as gas flow, zinc acetate solution concentrations, and substrate temperatures, all of which have an effect on the performance of stability of MAPbI3 solar cells. Also, the low hysteresis reported for these samples was discussed in this study. We have also observed that long-term structural evolution of perovskite film also depends on the ZnO substrate and its deposition method

Analysis of the UV ozone-treated SnO2 electron transporting layer in planar perovskite solar cells for high performance and reduced hysteresis

Tin oxide (SnO2) is widely used as electron transporting layer (ETL) in perovskite solar cells (PSCs) because its good transparency, band alignment to perovskite and stability. The interface between the ETL and the perovskite in the PSCs affects the charge extraction process and may influence the optoelectronic properties. Surface treatment of SnO2, such as the UV-ozone (UVO) treatment has been shown to enhance the efficiency and reduce the light soaking effect of the PSCs. Herein, we report the success in control and suppressing hysteresis reaching as highest photoconversion efficiency 19.4% with negligible hysteresis for the devices growth on 60 minutes UVO treated SnO2. The wettability of treated SnO2 is well-matched with the polar solvent of the perovskite solution, leading to complete coverage of the substrate, although the treatment does not affect the morphology and the crystallinity of the perovskite thin films. Impedance spectroscopy measurements analysis, clearly indicate the decrease of recombination rate after UVO treatment and the reduction of low frequency capacitance causing a reduction of current-potential curve hysteresis

Structural and Electrical Investigation of Cobalt-Doped NiOx/Perovskite Interface for Efficient Inverted Solar Cells

Inorganic hole-transporting materials (HTMs) for stable and cheap inverted perovskite-based solar cells are highly desired. In this context, NiOx, with low synthesis temperature, has been employed. However, the low conductivity and the large number of defects limit the boost of the efficiency. An approach to improve the conductivity is metal doping. In this work, we have synthesized cobalt-doped NiOx nanoparticles containing 0.75, 1, 1.25, 2.5, and 5 mol% cobalt (Co) ions to be used for the inverted planar perovskite solar cells. The best efficiency of the devices utilizing the low temperature-deposited Co-doped NiOx HTM obtained a champion photoconversion efficiency of 16.42%, with 0.75 mol% of doping. Interestingly, we demonstrated that the improvement is not from an increase of the conductivity of the NiOx film, but due to the improvement of the perovskite layer morphology. We observe that the Co-doping raises the interfacial recombination of the device but more importantly improves the perovskite morphology, enlarging grain size and reducing the density of bulk defects and the bulk recombination. In the case of 0.75 mol% of doping, the beneficial effects do not just compensate for the deleterious one but increase performance further. Therefore, 0.75 mol% Co doping results in a significant improvement in the performance of NiOx-based inverted planar perovskite solar cells, and represents a good compromise to synthesize, and deposit, the inorganic material at low temperature, without losing the performance, due to the strong impact on the structural properties of the perovskite. This work highlights the importance of the interface from two different points of view, electrical and structural, recognizing the role of a low doping Co concentration, as a key to improve the inverted perovskite-based solar cells’ performance

Millisecond radiative recombination in poly(phenylene vinylene)-based light-emitting diodes from transient electroluminescence

The current and electroluminescence transient responses of standard poly(phenylene vinylene)-based light-emitting devices have been investigated. The electroluminescence time response is longer (milliseconds scale) than the current switch-off time by more than one order of magnitude, in the case of small area devices (<0.1 cm2). For large area devices ( ∼ 6 cm2) the electroluminescence decay time decreases from 1.45 ms to  ∼ 100 μs with increasing bias voltage. The fast current decay limits the electroluminescence decay at higher voltages. Several approaches are discussed to interpret the observed slow decrease of electroluminescence after turning off the bias. One relies upon the Langevin-type bimolecular recombination kinetics which is governed by the minority carriers (electrons), and another focuses on the slow release of trapped electrons as possible explanations. Additionally, we show that the device current density is mainly determined by the transport of the fastest carriers (holes)[email protected]

New iridium complex as additive to the spiro-OMeTAD in perovskite solar cells with enhanced stability

A new iridium complex, IrCp*Cl(PyPyz)[TFSI], has been synthesized and used as additive for the hole transporter material, spiro-OMeTAD, in perovskite solar cells. The cells prepared with this Ir additive present higher efficiency than reference cells, and similar to cells prepared with Co additive. We have determined that the presence of metal complexes as additives decreases the recombination rate, as it has been observed by impedance spectroscopy. Very interestingly, while the efficiency after 3 months decreases by 22% and 70% for reference cell and cell with Co additive, respectively, the efficiency of devices containing the Ir additive is only decreased by a 4%

Up-Converting Lanthanide-Doped YAG Nanospheres

The development of lanthanide-doped Y3Al5O12 (Ln:YAG) garnet nanostructures is a hot topic in the field of inorganic nanophosphors due to the current interest in developing small nanoparticles for solid-state lighting (SSL), displays, lasers and scintillation applications. In this study, we report the preparation of homogeneous Ln:YAG (Ln: Ho/Yb ions) nanospheres through a combined two-steps coprecipitationsolvothermal synthesis at low temperature. The crystal growth takes place in ethylene glycol, which is an inexpensive, non-toxic and easily available solvent. Monodisperse and crystalline spherical YAG particles of 80 nm in diameter were obtained. Furthermore, the protocol can be extended to other compositions (Tb/Yb, Tm/Yb. . .) to explore different luminescent properties, without affecting the morphology of the material, indicating the robustness and practical utility of the reported methodology. Thermal treatment of the nanogarnets at 1200◦C is necessary for making materials optically active upon both UV and NIR excitation. The spherical morphology of annealed samples is preserved, what helps their further dispersion in solvents, barbotines, inks or printing vehicles. The lanthanide-doped nanogarnets exhibited the characteristic blue, green and red emissions from lanthanide upconversion photoluminescence (UCPL) upon NIR excitation. The UCPL mechanism was studied and CIE chromate coordinates were obtained. These nanogarnets were further evaluated as functional ceramic phosphors by incorporating them into commercial glazes. The materials exhibited an exceptional chemical stability in a harsh medium such as a fused glaze. Consequently, the visible emissions of the nanoparticles were transferred to the whole glass matrix, thus providing a functional glaze that emits intense blue and green light upon NIR excitation. These luminescent nanogarnets have promising applications in smart enamels, but can also be useful for lighting displays (white LEDs. . .), smart paintings or plastics, and anti-counterfeiting systems

Triplication of the photocurrent in dye solar cells by increasing the elongation of the π-conjugation in Zn-porphyrin sensitizers

Porphyrins are promising sensitizers for dye solar cells (DSCs) but narrow absorption bands at 400-450 and 500-650 nm limit their light-harvesting properties. Increasing elongation of the π-conjugation and loss of symmetry causes broadening and a red-shift of the absorption bands, which considerably improves the performance of the DSC. Herein we use an oligothienylenevinylene to bridge a Zn-porphyrin system and the anchoring group of the sensitizer. We separately study the performance of the two basic units: oligothienylenevinylene and Zn-porphyrin. The combined system provides a three-fold enhancement of the photocurrent with respect to parent dyes. This is caused by an additional strong absorption in the region 400-650 nm that leads to flat IPCE of 60%. Theoretical calculations support that the addition of the oligothienylenevinylene unit as a linking bridge creates a charge transfer band that transforms a Zn-porphyrin dye into a push-pull type system with highly efficient charge injection propertie

Water Oxidation at Hematite Photoelectrodes with an Iridium-Based Catalyst

The iridium complex [Cp*Ir(H2O)3](SO 4) was used as an organometallic source for the electrodeposition of iridium oxide onto Fe2O3. The new iridium-containing electrode allowed us to study the coupling between the photocatalytic properties of hematite and the electrocatalytic properties of the iridium-based material. A cathodic shift of the photocurrent for water oxidation upon electrodeposition of the iridium complex was observed, which increased with increasing surface concentration of IrOx on Fe2O3. The shift for the highest surface concentration of iridium tested amounts to 300 mV at 200 μA·cm-2 current density. The catalytic mechanism of the IrOx layer was unveiled by impedance spectroscopy measurements fitted to a physical model and can be explained on the basis of a highly capacitive layer, which enhances charge separation and stores photogenerated holes at Fe2O3, subsequently oxidizing water. These findings improve our understanding of the mechanism of water oxidation by heterogeneous Ir-based catalysts coupled to semiconductor electrodesJ.B. acknowledges support by projects from Ministerio de Economía y Competititvidad (MINECO) of Spain (Consolider HOPE CSD2007-00007) and Generalitat Valenciana (PROMETEO/2009/058). F.F.S. thanks the funding of University Jaume I- Bancaixa (Grant P1·1B2011-50). S.G. acknowledges support by MINECO of Spain under the Ramon y Cajal programme. Mrs. Encarna Blasco from the Instituto Tecnológico de Cerámica is acknowledged for carrying out the structural characterization by XPS. The SCIE of Universidad de Valencia is acknowledged for the SEM images

Widening the 2D/3D Perovskite Family for Efficient and Thermal-Resistant Solar Cells by the Use of Secondary Ammonium Cations

While 2D/3D layered perovskites have been the object of comprehensive research principally focused on increasing the long-term stability observed in 3D perovskites, significant opportunities still exist concerning the application of different kinds of cations outside the sphere of primary amines, which are the cations most usually applied. Our results demonstrate that the materials and the solar cells prepared with dipropylammonium iodide (DipI), a bulky secondary ammonium cation of small size, lead to obtaining materials that are not only efficient and thermodynamically stable but also robust toward heat stress. Time-resolved studies indicate longer carrier lifetime for 2D/3D layered perovskites fabricated with this bulky cation than for systems based on bulky primary ammonium cations, which allowed us to obtain PCE = 12.51% (n = 10), 15.78% (n = 50), and 17.90% (n = 90). We determine that the concentration of perovskite material after 240 min at 100 °C is up to 575% greater in the 2D/3D perovskite (n = 10) than that observed in 3D perovskite films. The material stability also improves the thermal stability of the photovoltaic devices, presenting an efficiency drop of just 4% for n = 50 and n = 10 after thermal annealing while the performance drop for reference 3D samples in the same conditions was greater than 80%