Energetic disorder in perovskite/polymer solar cells and its relationship with the interfacial carrier losses

Previous reports have observed a direct relationship between the polymer poly(3-hexylthiophene) molecular weight (MW) and the perovskite solar cell (PSC) efficiency. Herein, we analyse how the differences in MW and the differences in energetic disorder influence the interfacial carrier losses in the PSCs under operation conditions and explain the observed differences

PROTECTING OUR CROPS - APPROACHES FOR PLANT PARASITIC NEMATODE CONTROL

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Inverted vs Standard PTB7:PC70BM Organic Photovoltaic Devices. The benefit of highly selective and extracting contacts in device performance

In this work we compare the photovoltaic performance of different cell designs, standard and inverted, for one of the most promising systems to achieve power conversion efficiencies over 10% in polymer:fullerene single cells, namely PTB7:PC70BM. Impedance spectroscopy, charge extraction and transient photovoltage are used in order to assign the electrical losses initially observed in the current density–voltage curve and understand the main limitation of every design. While inverted devices show competitive performance in terms of charge generation, transport of carriers and also for charge collection at electrodes, standard devices present additional resistive losses that are assigned to charge transfer issues at the active layer/anode interface. This additional resistance increase the overall series resistance of devices, lowers the fill factor and it is the ultimate responsible for the observed reduced device performance of standard cells in comparison to inverted ones. In this way, devices over 7.2% are reported with ZnO and MoO3 as interlayer electrodes that act as improved highly selective and extracting contacts in comparison to standard PEDOT:PSS and Ca/Ag. Contacts are thus electrically optimized. Additional improvement of device performance must consider enhancement of intrinsic recombination properties of the blend. Lower molecular weights and/or any residual catalyst impurities with respect to other batches are the only limitation to reach record efficiencies as those shown in recent works

Charge carrier transport and contact selectivity limit the operation of PTB7-based organic solar cells of varying active layer thickness

In this work we study the different electrical loss pathways occurring during the operation of bulk heterojunction solar cells by using a variety of electrical and optical characterization techniques beyond the current density–voltage curve (J–V): Impedance Spectroscopy (IS), Charge Extraction (CE) and Transient Photovoltage (TPV). Two sets of devices are analyzed: the first is based on the donor polymer P3HT, known to provide efficient cells using thick active layers (i.e. 270 nm), and the recently developed PTB7 which offers maximum efficiencies for devices with thinner layers (i.e. 100 nm). Devices fabricated with P3HT:PC60BM are not limited by transport of carriers and large active layer thickness may be used. Importantly, increasing the active layer thickness does not modify the contact selectivity. This is supported by analysis of the diode curve measured in the dark (similar leakage currents) and by capacitance–voltage measurements (similar fullerene content covering the cathode). Under these conditions the current density curve under illumination is mainly defined by the recombination processes taking place in the bulk of the active layer. In contrast, transport of carriers and contact selectivity are both limiting factors for the PTB7:PC60BM system. In this case, best efficiencies are obtained with a low active layer thickness and a high fullerene ratio. Reduced active layer thickness minimizes undesired electrical resistances related to carrier transport through the bulk of the active layer. High fullerene content enhances the amount of fullerene molecules at the cathode leading to decreased leakage currents. Then, the overall device efficiency will be a combination of the recombination kinetics in the bulk of the active layer, undesired resistance to transport of carriers and leakage current present due to low selectivity of the contact. The use of additives has also been explored which enhances charge generation and extraction. Overall, this work provides a comprehensive guide on how to interpret results obtained from some of the most widely used optoelectronic techniques employed to analyse operating devices

Novel spiro-core dopant-free hole transporting material for planar inverted Perovskite solar cells

Hole-transporting materials (HTMs) have demonstrated their crucial role in promoting charge extraction, interface recombination, and device stability in perovskite solar cells (PSCs). Herein, we present the synthesis of a novel dopant-free spiro-type fluorine core-based HTM with four ethoxytriisopropylsilane groups (Syl-SC) for inverted planar perovskite solar cells (iPSCs). The thickness of the Syl-SC influences the performance of iPSCs. The best-performing iPSC is achieved with a 0.8 mg/mL Syl-SC solution (ca. 15 nm thick) and exhibits a power conversion efficiency (PCE) of 15.77%, with Jsc = 20.00 mA/cm2, Voc = 1.006 V, and FF = 80.10%. As compared to devices based on PEDOT:PSS, the iPSCs based on Syl-SC exhibit a higher Voc, leading to a higher PCE. Additionally, it has been found that Syl-SC can more effectively suppress charge interfacial recombination in comparison to PEDOT:PSS, which results in an improvement in fill factor. Therefore, Syl-SC, a facilely processed and efficient hole-transporting material, presents a promising cost-effective alternative for inverted perovskite solar cells

Crítica a los cursores de SQL y propuesta de su eliminación

A través de un análisis exhaustivo de estructuras de programas se muestra que los cursores de SQL son innecesarios para elaborar tablas. Se resalta la incompatibilidad entre los cursores y el estilo descriptivo y funcional de la sintaxis y que su uso destruye el potencial paralelismo en la ejecución. Se señalan restricciones arbitrarias a la generalidad que limitan el poder expresivo del lenguaje SQL.Using an exhaustive analysis of possible program structures we show that SQL cursors are not necessary to compute tables. We highlight the incompatibility between cursors and the descriptive and functional syntax style. The use of cursors also destroys the potential parallelism in execution. We show how arbitrary restrictions in the structure of the SQL language bound the languages expressive power.IV Workshop de Ingeniería de Software y Base de DatosRed de Universidades con Carreras en Informática (RedUNCI

Crítica a los cursores de SQL y propuesta de su eliminación

A través de un análisis exhaustivo de estructuras de programas se muestra que los cursores de SQL son innecesarios para elaborar tablas. Se resalta la incompatibilidad entre los cursores y el estilo descriptivo y funcional de la sintaxis y que su uso destruye el potencial paralelismo en la ejecución. Se señalan restricciones arbitrarias a la generalidad que limitan el poder expresivo del lenguaje SQL.Using an exhaustive analysis of possible program structures we show that SQL cursors are not necessary to compute tables. We highlight the incompatibility between cursors and the descriptive and functional syntax style. The use of cursors also destroys the potential parallelism in execution. We show how arbitrary restrictions in the structure of the SQL language bound the languages expressive power.IV Workshop de Ingeniería de Software y Base de DatosRed de Universidades con Carreras en Informática (RedUNCI

Gene expression changes in diapause or quiescent potato cyst nematode, Globodera pallida, eggs after hydration or exposure to tomato root diffusate

The authors thank the Education Spanish Ministry for the grant provided for the first author under the "Ayudas para la movilidad postdoctoral en centros extranjeros'' scheme. The James Hutton Institute receives funding from the Scottish Government.Plant-parasitic nematodes (PPN) need to be adapted to survive in the absence of a suitable host or in hostile environmental conditions. Various forms of developmental arrest including hatching inhibition and dauer stages are used by PPN in order to survive these conditions and spread to other areas. Potato cyst nematodes (PCN) (Globodera pallida and G. rostochiensis) are frequently in an anhydrobiotic state, with unhatched nematode persisting for extended periods of time inside the cyst in the absence of the host. This paper shows fundamental changes in the response of quiescent and diapaused eggs of G. pallida to hydration and following exposure to tomato root diffusate (RD) using microarray gene expression analysis encompassing a broad set of genes. For the quiescent eggs, 547 genes showed differential expression following hydration vs. hydratation and RD (H-RD) treatment whereas 708 genes showed differential regulation for the diapaused eggs following these treatments. The comparison between hydrated quiescent and diapaused eggs showed marked differences, with 2,380 genes that were differentially regulated compared with 987 genes following H-RD. Hydrated quiescent and diapaused eggs were markedly different indicating differences in adaptation for long-term survival. Transport activity is highly up-regulated following H-RD and few genes were coincident between both kinds of eggs. With the quiescent eggs, the majority of genes were related to ion transport (mainly sodium), while the diapaused eggs showed a major diversity of transporters (amino acid transport, ion transport, acetylcholine or other molecules).Publisher PDFPeer reviewe

Estudio comparativo de varios factores de la personalidad situacional en alumnos universitarios del grado en magisterio y su repercusión en el proceso enseñanza-aprendizaje

La enseñanza universitaria se trata de un proceso en permanente cambio que requiere toda la atención e innovación necesarias para establecer un conocimiento bien afianzado que permita mejorar la calidad del proceso enseñanza-aprendizaje. La siguiente investigación tiene como objetivo evidenciar la relación existente entre las variables estabilidad emocional, eficacia y ansiedad. Se pretende dar respuesta a las posibles necesidades del alumnado, tanto desde la prevención como de la intervención, en una muestra de alumnado del grado en magisterio en la Universidad de Castilla-La Mancha, España. Se concluye, que la personalidad es un producto de las relaciones sociales y es un constructo que sirve para categorizar, ante todo, la conducta socia