Characterisation and Optimisation of the Hole Transport Interface in Organic Solar Cells for Improved Performance and Stability of the Devices

The increased atmospheric concentration of greenhouse gases due to the combustion of fossil fuels and its impact on the temperature of the planet has led to the development of alternative energy generation methods. Organic solar cells (OSCs) are a promising technology that is simple to process, flexible, customizable, and potentially low-cost. However, relatively low efficiencies, and short lifetimes compared with other photovoltaic technologies are as the main challenges of organic solar cells. This thesis aims to characterise and optimise the hole transporting interface to improve the efficiency and long-term stability of OSCs. To achieve this, first, the device fabrication process of P3HT:PCBM based devices was optimised to produce devices that perform at a standard commensurate with those reported in literature with a similar architecture and fabricated under similar conditions. In particular, two different evaporation techniques for the deposition of the electron conducting electrode were compared. Electron-beam evaporation significantly decreased the crystallinity of P3HT while thermal evaporation proved to be effective for producing P3HT and PCDTBT based devices with an efficiency comparable to the values reported in literature for a similar device architecture. In an attempt to improve the efficiency of devices, the electrical conductivity of the PEDOT:PSS hole transporting layer was increased by almost two orders of magnitude using a zwitterionic additive (DYMAP) to dope the PEDOT:PSS dispersion. The liquid and solid phase structural modifications of the conductivity enhanced PEDOT:PSS were studied to understand the effects of conductivity enhancing additives on the morphology of PEDOT:PSS. Small angle neutron scattering revealed that the interchain distance between PSS backbone chains, and the screening length of neutralised PSS segments increase as the concentration of DYMAP increases from 0 to 25 mM. However, at 30 mM doping concentration, DYMAP induces gelation in the PEDOT:PSS dispersion resulting in a decreased interchain distance similar to that of the undoped PEDOT:PSS, and a significantly increased screening length compared to that of the 25 mM doped dispersion. The vertical structure of DYMAP doped PEDOT:PSS films was studied with neutron reflectivity which revealed that at low doping concentration, the film separates into a quasi-bilayer film in which the dopant segregates at the bottom of the film. However, at higher DYMAP doping concentration, DYMAP is evenly distributed throughout the film which results in a homogeneous single structure. The DYMAP doped PEDOT:PSS films were then incorporated as the hole transporting layer in OSCs which resulted in the decreased photovoltaic performance of devices compared to the control devices. This was found to be mainly due to the poor contact between the doped HTL and the active layer as a result of the increased phobicity of the doped PEDOT:PSS films to the solvent of the active layer. Another approach to improving the device efficiency and stability was to incorporate three variants of a P3HT50-b-PSSx block co-polymer as an interfacial layer between PEDOT:PSS and P3HT:PCBM to improve the hole transport and stability between such layers. The incorporation of a 10 nm P3HT50-b-PSS16 and a 13 nm P3HT50-b-PSS23 interfacial layer resulted in a 9% and 12% increased device efficiency respectively compared to the reference devices. This was mainly due to a 9% increase of the open circuit voltage caused by the more energetically favourable alignment of the HOMO of the block co-polymers with the HOMO of P3HT. The fill factor of the 10 nm P3HT50-b-PSS16 and 13 nm P3HT50-b-PSS23 incorporated devices also increased by 2.8% and 6.2% respectively due to a smoother surface than PEDOT:PSS and the more compatible contact between the P3HT block of the block co-polymer and the P3HT, and the PSS block with the PEDOT:PSS. Moreover, the devices with the interfacial block co-polymer had a higher normalised efficiency than the control devices after 2200 hours of storage, demonstrating that the block co-polymer not only improves device efficiency, but crucially prevents degradation by stabilising the interface between PEDOT:PSS and P3HT

Equilibration of Concentrated Hard Sphere Fluids

We report a systematic molecular dynamics study of the isochoric equilibration of hard-sphere fluids in their metastable regime close to the glass transition. The thermalization process starts with the system prepared in a non-equilibrium state with the desired final volume fraction {\phi} but with a prescribed non-equilibrium static structure factor S_0(k; {\phi}). The evolution of the {\alpha}- relaxation time {\tau}{\alpha} (k) and long-time self-diffusion coefficient DL as a function of the evolution time tw is then monitored for an array of volume fractions. For a given waiting time the plot of {\tau}{\alpha} (k; {\phi}, tw) as a function of {\phi} exhibits two regimes corresponding to samples that have fully equilibrated within this waiting time ({\phi} \leq {\phi}(c) (tw)), and to samples for which equilibration is not yet complete ({\phi} \geq {\phi}(c) (tw)). The crossover volume fraction {\phi}(c) (tw) increases with tw but seems to saturate to a value {\phi}(a) \equiv {\phi}(c) (tw \rightarrow \infty) \approx 0.582. We also find that the waiting time t^(eq)_w({\phi}) required to equilibrate a system grows faster than the corresponding equilibrium relaxation time, t^(eq)({\phi}) \approx 0.27 \times [{\tau}{\alpha} (k; {\phi})]^1.43, and that both characteristic times increase strongly as {\phi} approaches {\phi}^(a), thus suggesting that the measurement of equilibrium properties at and above {\phi}(a) is experimentally impossible

Improved Performance and Stability of Organic Solar Cells by the Incorporation of a Block Copolymer Interfacial Layer

In a proof-of-concept study, this work demonstrates that incorporating a specifically designed block copolymer as an interfacial layer between a charge transport layer and the photoactive layer in organic solar cells can enhance the interface between these layers leading to both performance and stability improvements of the device. This is achieved by incorporating a P3HT50-b-PSSx block copolymer as an interfacial layer between the hole transporting and photoactive layers, which results in the improvement of the interfacial roughness, energy level alignment, and stability between these layers. Specifically, the incorporation of a 10 nm P3HT50-b-PSS16 and a 13 nm P3HT50-b-PSS23 interfacial layer results in a 9% and a 12% increase in device efficiency respectively compared to the reference devices. In addition to having a higher initial efficiency, the devices with the block copolymer continue to have a higher normalized efficiency than the control devices after 2200 h of storage, demonstrating that the block copolymer not only improves device efficiency, but crucially, prevents degradation by stabilizing the interface between the hole transporting layer and the photoactive layer. This study proves that appropriately designed and optimized block copolymers can simultaneously stabilize and improve the efficiency of organic solar cells

Multi-site observations of Delta Scuti stars 7 Aql and 8 Aql (a new Delta Scuti variable): The twelfth STEPHI campaign in 2003

We present an analysis of the pulsation behaviour of the Delta Scuti stars 7 Aql (HD 174532) and 8 Aql (HD 174589) -- a new variable star -- observed in the framework of STEPHI XII campaign during 2003 June--July. 183 hours of high precision photometry were acquired by using four-channel photometers at three sites on three continents during 21 days. The light curves and amplitude spectra were obtained following a classical scheme of multi-channel photometry. Observations in different filters were also obtained and analyzed. Six and three frequencies have been unambiguously detected above a 99% confidence level in the range 0.090 mHz--0.300 mHz and 0.100 mHz-- 0.145 mHz in 7 Aql and 8 Aql respectively. A comparison of observed and theoretical frequencies shows that 7 Aql and 8 Aql may oscillate with p modes of low radial orders, typical among Delta Scuti stars. In terms of radial oscillations the range of 8 Aql goes from n=1 to n=3 while for 7 Aql the range spans from n=4 to n=7. Non-radial oscillations have to be present in both stars as well. The expected range of excited modes according to a non adiabatic analysis goes from n=1 to n=6 in both stars.Comment: 8 pages, 7 fugures, 5 tables, accepted for publication in Astronomical Journa

Hongos micorrizícos arbusculares y vermicomposta en el crecimiento de papaya (Carica papaya L) en invernadero

Objective: To evaluate arbuscular mycorrhizal fungi (AMF) inoculation and the application of vermicompost (V), on papaya (Carica papaya L) plant growth in greenhouse. Design/methodology/approach: Rhizophagus intraradices (RI), a Barranca de las Nueces (BN) native consortium and without AMF with three proportions of vermicompost in the substrate (0, 1 and 10% v/v), were evaluated using a completely randomized bifactorial design. After 90 days of establishment, variables of plant growth and mycorrhizal colonization were recorded. A variance analysis and Tukey test (P?0.05) of data were made. Results:  A significant effect of the vermicompost factor and the interaction of the factors (AMF x V) was found. The largest size of the plants with the highest proportion of vermicompost was recorded. The highest colonization was achieved with the BN inoculum. Regarding the interaction, it was found that the growth of the plants was greater as the vermicompost increased, but this was affected by the AMF inoculum. Limitations on study/implications: No significant effect of the inoculum factor on the growth of the plants was found and the application of vermicompost to the substrate limits the AMF plant growth promoting. Findings/conclusions: The growth of papaya plants was favored by inoculation with AMF, but is determined by the amount of organic matter present in the substrate. High concentrations of vermicompost limit the benefit that mycorrhiza can contribute to the growth of papaya in greenhouse.Objetivo: Evaluar la inoculación con Hongos Micorrízicos Arbusculares (HMA) y aplicación de vermicomposta (V), en el crecimiento de plantas de papaya (Carica papaya L) en invernadero. Diseño/metodología/aproximación: Se estableció un diseño bifactorial completamente al azar, y se evaluó a Rhizophagus intraradices (RI), un consorcio nativo Barranca de las Nueces (BN) y sin HMA con tres proporciones de vermicomposta en el sustrato (0, 1 y 10% v/v). A los 90 d del establecimiento, se registraron variables de crecimiento de las plantas y la colonización micorrízica. A los datos se les realizó un análisis de varianza y pruebas de comparación de medias (P?0.05). Resultados: Se encontró efecto significativo del factor vermicomposta y de la interacción de los factores (HMA x V). Se registró el mayor tamaño de las plantas a mayor proporción de vermicomposta. Se alcanzó la mayor colonización con el inóculo BN. Respecto a la interacción, el crecimiento de las plantas fue mayor a medida que se incrementó la vermicomposta, pero fue afectado por el inóculo de HMA. Limitaciones del estudio/implicaciones: No se obtuvieron efectos significativos del factor inóculo en el crecimiento de las plantas; y la aplicación de vermicomposta al sustrato limita el efecto promotor de crecimiento de los HMA. Hallazgos/conclusiones: El crecimiento de plantas de papaya es favorecido por la inoculación con HMA, pero es determinado por la cantidad de materia orgánica presente en el sustrato. Altas concentraciones de vermicomposta, limitan el beneficio que la micorriza puede aportar en el crecimiento de la papaya en invernadero

Measurement of L-shell emission from mid-Z targets under non-LTE conditions using Transmission Grating Spectrometer and DANTE power diagnostics

Producción CientíficaIn this work, we present the measurement of L-band emission from buried Sc/V targets in experiments performed at the OMEGA laser facility. The goal of these experiments was to study non-local thermodynamic equilibrium plasmas and benchmark atomic physics codes. The L-band emission was measured simultaneously by the time resolved DANTE power diagnostic and the recently fielded time integrated Soreq-Transmission Grating Spectrometer (TGS) diagnostic. The TGS measurement was used to support the spectral reconstruction process needed for the unfolding of the DANTE data. The Soreq-TGS diagnostic allows for broadband spectral measurement in the 120 eV–2000 eV spectral band, covering L- and M-shell emission of mid- and high-Z elements, with spectral resolution λ/Δλ = 8–30 and accuracy better than 25%. The Soreq-TGS diagnostic is compatible with ten-inch-manipulator platforms and can be used for a wide variety of high energy density physics, laboratory astrophysics, and inertial confinement fusion experiments

How to estimate the concentration of sugar in sodas? An introduction to the refractometry

Con el propósito de promover prácticas cotidianas que faciliten la construcción de nuevas maneras de enseñar y aprender ciencias es que presentamos una propuesta didáctica inscripta en un marco de educación científica escolar; cuyo punto de partida es una pregunta disparadora: ¿Cómo podrían estimar la concentración de azúcar en una bebida gaseosa?, una vez desarrollados los conceptos asociados a la reflexión-refracción de la luz en el aula. Se abordan en el aula de física conceptos de óptica geométrica: reflexión y refracción de la luz; integrando contenidos desarrollados en química como: soluciones químicas y concentración de las soluciones.In order to encourage daily practices that facilitate the construction of new ways of teaching and learning science is presented in a didactic framework enrolled at school science education, whose starting point is a triggering question: once developed the concepts associated with reflection-refraction of light in the classroom. How could estimate the concentration of sweet soda? It approaches concepts of geometrical optics in the physical classroom: reflection and refraction of light, integrating contents of chemical as chemical solutions and concentration calculation

From flax to wool: spinning at Cabezo Redondo (Villena, Alicante) and changes in textile production during the Bronze Age

En este trabajo se analiza el importante conjunto de fusayolas procedentes del asentamiento de Cabezo Redondo, recuperadas tanto en las excavaciones antiguas de José María Soler como en las desarrolladas en las últimas décadas. El número elevado de ejemplares, todas ellas correspondientes a contextos del Bronce Tardío (c. 1600-1250 cal BC), y sus características (diversidad en materiales utilizados, tipología y peso) permiten inferir una actividad de hilado intensa distribuida a lo largo del poblado, así como importantes transformaciones en la producción textil con respecto a los momentos previos. Entre los cambios principales se encontrarían la continuidad de la tradición de hilado de fibras vegetales como el lino y, sobre todo, la consolidación de nuevas técnicas de hilado y la generalización del hilado de fibras de origen animal como la lana. En definitiva, a partir del estudio de estos artefactos, sumado al análisis de otros indicadores, se propone el desarrollo de una producción textil amplia y diversa, en sintonía con lo que sucedido en otras áreas de Europa y el Mediterráneo durante la segunda mitad del II milenio cal BC.This paper analyses the important set of spindle whorls from the Cabezo Redondo settlement, recovered both in the ancient excavations of José María Soler and in the excavations carried out in recent decades. The large number of tools, all of them corresponding to Late Bronze Age contexts (c. 1600-1250 cal BC), and their characteristics -diversity in materials used, typology and weight- allow us to infer an intense spinning activity distributed throughout the settlement, as well as important transformations in textile production with respect to previous times. The main changes include the continuity of the tradition of spinning bast fibres such as flax and, above all, the consolidation of new spinning techniques and the generalisation of the spinning of animal fibres such as wool. In short, the study of these artefacts, together with the analysis of other indicators, suggests the development of a wide and diverse textile production, in line with what happened in other areas of Europe and the Mediterranean during the second half of the 2nd millennium BC

Ionization disequilibrium in K- and L-shell ions

Producción CientíficaTime-gated Sc K-shell and Ge L-shell spectra are presented from a range of characterized thermodynamic states spanning ion densities of 1e19-1e20cm-3 and plasma temperatures around 2000eV. For the higher densities studied and temperatures from 1000 to 3000 eV, the Sc and Ge x-ray emission spectra are consistent with steady-state calculations from the modern atomic kinetics model SCRAM. At the lower ion densities achieved through plasma expansion, however, the model calculations require a higher plasma temperature to reproduce the observed Ge spectrum. We attribute this to ionization disequilibrium of the Sc because the ionization time scales exceed the hydrodynamic timescale when the inferred temperatures diverge.This work has been supported by the Research Grant No. PID2019-108764RB-I00 from the Spanish Ministry of Science and Innovation

Phase imaging of irradiated foils at the OMEGA EP facility using phase-stepping X-ray Talbot–Lau deflectometry

Producción CientíficaDiagnosing the evolution of laser-generated high energy density (HED) systems is fundamental to develop a correct understanding of the behavior of matter under extreme conditions. Talbot–Lau interferometry constitutes a promising tool, since it permits simultaneous single-shot X-ray radiography and phase-contrast imaging of dense plasmas. We present the results of an experiment at OMEGA EP that aims to probe the ablation front of a laser-irradiated foil using a Talbot–Lau X-ray interferometer. A polystyrene (CH) foil was irradiated by a laser of 133 J, 1 ns and probed with 8 keV laser-produced backlighter radiation from Cu foils driven by a short-pulse laser (153 J, 11 ps). The ablation front interferograms were processed in combination with a set of reference images obtained ex situ using phase-stepping. We managed to obtain attenuation and phase-shift images of a laser-irradiated foil for electron densities above 1e22 cm−3. These results showcase the capabilities of Talbot–Lau X-ray diagnostic methods to diagnose HED laser-generated plasmas through high-resolution imaging.The work has been supported by Research Grant No. PID2019-108764RB-I00 from the Spanish Min istry of Science and Innovatio