Dispositivos optoelectrónicos basados en perovskitas orgánico-inorgánico conteniendo el catión guanidinio

La presente investigación se enfoca en el campo de dispositivos optoelectrónicos, concretamente en células solares basadas en perovskitas hibrídas orgánicas-inorgánicas, las cuales han emergido recientemente como un material prometedor para complementar o reemplazar a las actuales células solares basadas en silicio (Si). Los investigadores del Departamento de Química Física y Termodinámica Aplicada/ Instituto de Química Fina y Nanoquímica (UCO) en colaboración con el Group of Molecular Engineering of Functional Materials (EPFL) han logrado introducir el catión Guanidinio (Gua) en la red cristalina de la perovskita MAPbI3, basada en metilamonio (MA) y yoduro de plomo (PbI2), sustituyendo hasta un 25% de MA por Gua. Estos resultados son sorprendentes debido a que el radio catiónico del Guanidinio está por encima del límite de tolerancia de Goldsmith (0.8-1), el cual predice la formación de una estructura cristalina cubica. Este nuevo material GuaxMA(1-x)PbI3 (0 ≤ x ≤ 0.25) presenta una mayor estabilidad a la humedad y al oxígeno que su antecesor el MAPbI3. Además, conserva sus propiedades ópticas, las cuales fueron verificadas al fabricar células solares de alta eficiencia (hasta un 20%) y sometiéndolas a un test de estrés de mil horas bajo iluminación constante y a una temperatura de 65ºC (equivalente a 1333 días bajo condiciones normales). Este hallazgo abre la puerta a la incorporación de nuevas especies con radios catiónicos que excedan el límite teórico de Goldsmith

Mechanics of Growth and Coalescence of Pre-existing Voids in a Ductile Matrix

This research project experimentally and numerically investigates the growth and coalescence of pre-existing voids for a wide range of stress states in a ductile matrix with a special focus on shear dominated loading conditions and presents quantitative kinetics data for these processes. The results obtained contribute to further development of current fracture models by generating reliable experimental data for void growth and coalescence, which can be used to evaluate the existing fracture models. A lead-containing copper alloy has been selected as model material, in which lead inclusions act as pre-existing voids – as demonstrated by unit cell numerical simulations for a wide range of stress states. A second copper alloy of similar composition, but without lead allows us to obtain mechanical properties of the matrix. By comparing the behavior of the two alloys it is possible to evaluate the effect of the voids on the macroscopic mechanical behavior. The model materials are deformed and fractured in combined torsion / tension tests and notched tensile tests to subject them to the desired wide range of stress triaxialities. Quantitative fractography and metallography provide the desired kinetics data on void shape, size and orientation, that can be correlated with numerical simulations, as well as existing void growth and coalescence models. The influence of stress-state and micro-structural characteristics on void growth and void coalescence – particularly for zero nominal stress triaxiality conditions – is illustrated at the hand of the results of the investigation. Contrary to the predictions of current micromechanical models, significant growth of small voids resulting in moderate increases in the total void volume is observed in torsion specimens. This growth may be triggered by the developing texture of the matrix material and particularly by twinning. By means of FEM computations with 3D single cell simulations comprising initially ellipsoidal voids, the effect of the initial texture and texture evolution is emphasized. The numerical results showed that the experimentally observed texture of the material accelerates void growth under relatively high stress triaxialities, and possibly allows growth of small voids under low and zero stress triaxialities. The initial shape of the lead inclusions and possibly their growth, was found to be dependent on their initial size. These results emphasize the need for a complete and rather detailed modeling of microstructural and deformation features in order to model damage process correctly. The presented work contributes to a better understanding of void growth and coalescence fracture processes, particularly under shear dominated loading conditions

Business School Perceptions of the Possible Impact of the Teaching Excellence Framework: A Complex Adaptive Systems Perspective.

The implementation of the Teaching Excellence Framework (TEF) at institutional level 2017, presents universities with the challenge of responding to a government policy which has the capacity to change the Higher Education landscape. Educational policies are capable of introducing complexity into organisations and inspiring disruptive behaviour. The strategic response to policy implementation within universities is often thought to be the domain of business schools due to their assumed autonomy and links to management. The responses of business schools towards policy implementation have not been previously explored. Therefore, the research explores the response of business schools towards the Institutional level TEF as well as wider policy changes, within the context of an assumed sense of autonomy. An interpretivist research methodology was chosen in order to explore business school responses towards the voluntary participation of the TEF in 2017 through interviews with respondents from universities across the country. This includes analysis of sense making from respondents as they drawing upon their respective knowledge networks. Qualitative research was utilised in order to explore the response from business schools and increase the understanding of policy response within the Higher Education sector. The research utilised purposive sampling followed by the use of snowball sampling. Complex Adaptive Systems theory was used a theoretical lens, and the data was explored though the use of thematic analysis which examined cluster formations in NVivo and identified patterns of data emerging into four main CAS areas. The findings suggest that business school responses towards the Institutional Level TEF in 2017 represents a moment in time when participating universities found themselves responding to an educational policy which contained an evolutionary element, capable of introducing change into the existing order - thus providing an example of punctuated equilibrium. The response to the TEF was hierarchical, and involved individuals reporting to their respective Vice Chancellors, while receiving support from self-regulating groups. The TEF is identified as a Complex Adaptive System due to its none-linear and unpredictable behaviour. Finally, Zimmerman’s Zone of Complexity is utilised in order to illustrate the manner in which the Edge of Chaos is capable of representing an opportunity for innovative though, when the decision is made to alternate between managerial clockware and innovative swarmwar

AUTISM AND THE PERPETUAL PUZZLE: A RHETORICAL ANALYSIS OF THREE EXPLANATIONS FOR AUTISM

Autism awareness has increased in recent years in part because it is marked by confusion and controversy. The confusion and controversy stem from the fact that there are many beliefs about autism but little agreement. In this dissertation I examined the rhetoric produced by three primary groups?professional autism experts, caregivers to children with autism and mainstream media. In particular, I studied how each group explains autism. Explanations are vehicles for persuasion; they advance particular viewpoints about an illness. I conducted a rhetorical analysis of the three discourses produced by these groups, highlighting the most cohesive themes to emerge from the discourse. To study professional autism experts? explanations, I analyzed articles in autism?s flagship research journal and research articles from other journals and key books for additional insight. A computer metaphor guided expert explanations of autism. To define autism through one of most advanced and culturally accepted technological devices lent significant credibility to the explanations. Next, I studied the caregiver explanations, first conducting interviews with 19 parents to children with autism and then I analyzed the transcripts. Caregivers described autism as a social pathology; their children with autism were different and distant, or alien-like. The pathology affected people with autism, their caregivers and their families, many other neuro-typical people, and it also determined the course of treatment for the person with autism. Finally, mainstream media often explained autism in terms of its conflicts, framing its explanations of autism with a war metaphor. The vaccine debate received a significant attention, recharacterizing the role of medical institutions and health practitioners. Caregivers became the heroes, using their personal experiences as weapons against healthcare practitioners and their science. Caregivers also dealt with the invasion of autism, struggling for ways to return their children closer to the boundary that exists between the child with autism and the neuro-typical child

Synthesis and characterization of hybrid perovskites and their implementation in solar cells

En la presente Tesis, se ha estudiado la síntesis, caracterización y estabilidad de perovskitas hibridas orgánico – inorgánicas utilizando el catión plomo (Pb2+) para la red inorgánica y usando distintos tipos de cationes orgánicos (guanidinio, metilamonio y formamidinio). Además, se fabricaron células solares utilizando como material activo estas perovskitas y se estudió su rendimiento fotovoltaico y estabilidad frente a condiciones ambientales en condiciones operativas. Por último, se ha realizado un trabajo bibliográfico sobre perovskitas alternativas a las tradicionales que actualmente se emplean para células solares. La organización de los resultados experimentales se ha realizado conforme a la modalidad de compendio de artículos de la Universidad de Córdoba, según la cual, la Tesis doctoral estará constituida por las copias completas de los artículos científicos publicados o aceptados por el Doctorando. Además, se incluyen los objetivos, resumen, introducción y conclusiones. La introducción que consta del Capítulo I toca aspectos básicos que han sido tratados en los artículos. Así la introducción queda dividida en 5 bloques. En el primer bloque, se hace un breve repaso sobre la energía solar y su impacto en la actualidad y las diferentes tecnologías empleadas en fotovoltaica. En el segundo bloque, se habla de las estructuras cristalinas básicas de las perovskitas y sus distintas dimensionalidades. En el tercer bloque, se abordan las propiedades y composiciones de las distintas perovskitas con aplicación en células solares. Para el cuarto bloque, se habla de los distintos métodos de síntesis y deposición en capa fina. Por último, en el quinto apartado se mencionan las distintas arquitecturas de las células solares y se describe el funcionamiento de estas. El Capítulo II, denominado Experimental, describe los diferentes métodos y técnicas más utilizadas durante esta Tesis junto con un pequeño marco teórico en cada apartado. El Capítulo III está compuesto por tres artículos científicos donde se muestran los resultados obtenidos de esta Tesis. o Memoria 1.- “Benign-by-Design Solventless Mechanochemical Synthesis of Three-, Two-, and One-Dimensional Hybrid Perovskites” En esta memoria se propone la mecano-síntesis como método alternativo a la preparación de perovskitas hibridas orgánico – inorgánicas. En este método no se utilizan disolventes orgánicos (DMSO, DMF) como en los métodos tradicionales de síntesis de perovskita, por esta razón se considera un método más benigno con el medio ambiente ya que no genera residuos orgánicos en el proceso de síntesis. Además, este proceso es rápido, simple y reproducible, con el añadido de poder obtenerse gran cantidad de material en polvo policristalino con alta pureza, el cual facilita considerablemente el proceso de caracterización. Para demostrar la validez de este método propuesto se sintetizaron cuatro perovskitas distintas, MAPbI3, FAPbI3, GuaPbI3, Gua2PbI4 (MA, FA y Gua son metilamonio, formamidinio y guanidinio, respectivamente) y se caracterizaron mediante difracción de rayos X, espectroscopia de absorción UV-vis, espectroscopia de fotoelectrones de rayos X (XPS) y microscopia de barrido electrónico (SEM). De las cuatro perovskitas descritas, tres de ellas ya habían sido sintetizadas y caracterizadas previamente, pero en este trabajo se sintetizó y caracterizó por primera vez una perovskita basada en guanidinio (GuaPbI3) con una estructura cuasi-1D en forma de cadena. Este resultado es significativo en el campo de las perovskita porque introduce un nuevo método para sintetizar nuevos materiales de este tipo. o Memoria 2.- “Large guanidinium cation mixed with methylammonium in lead iodide perovskites for 19% efficient solar cells” Las perovskitas con estructura tridimensional (Capitulo 1) presentan las mejores propiedades optoelectrónicas para su implementación en células solares pero poseen una baja estabilidad a la humedad y al oxígeno. Por esta razón se ha propuesto el uso del guanidinio en mezcla con metilamonio para formar una perovskita hibrida multi-catión orgánico y se ha verificado la inserción del guanidinio dentro de la red cristalina mediante difracción de rayos X utilizando el método de Williamson - Hall (Capítulo I). Además, se ha demostrado el incremento en la eficiencia de las células solares utilizando esta mezcla de cationes y un aumento en la estabilidad en un test de estrés bajo iluminación constante (Capítulo III). o Memoria 3.- “Alternative Perovskites for Photovoltaics” En la Memoria 3, se presentan los enfoques más recientes realizados para explorar e implementar materiales de perovskitas alternativos e innovadores en células solares. Se busca superar las principales limitaciones que tienen las perovskitas convencionales, incluida la estabilidad y la toxicidad. En esta revisión bibliográfica se recopilan estudios como la sustitución del Pb2+ por elementos del grupo 14 como el germanio eliminando el problema de la toxicidad. Además, se muestran diferentes estudios utilizando diferentes cationes como el etilamonio, rubidio, guanidinio así como perovskitas con diferentes dimensionalidades según su estequiometria y sobre todo la familia de perovskitas quasi-2D Ruddlesden – Popper entre otras.In this thesis, a study of the organic - inorganic hybrid perovskites using the lead cation (Pb2+) as the inorganic network and different organic cations (guanidinium, methylammonium and formamidinium) has been performed. In addition, solar cells were manufactured using these perovskites as the active material to study their photovoltaic performance and environmental stability under operating conditions. Lastly, a bibliographic work about alternative perovskites used for solar cells applications has been realized. The organization of the experimental results has been carried out according to the modality of compendium of articles of the University of Córdoba. The complete copies of the scientific articles published or accepted authored by the PhD student will constitute the doctoral thesis. In addition, the objectives, summary, introduction, and conclusions have been included. The introduction is divided into 5 blocks. In the first block, a brief review of the solar energy and its impact to the energy sector is discussed together with the different technologies used in photovoltaic. In the second block, the different crystalline structures of the perovskites and their different dimensionalities are revised. In the third block, the properties and compositions of the different perovskites and their application in solar cells are summarized. In the fourth block, the different methods of synthesis and deposition as thin film are described. Finally, in the fifth section, it is mentioned the different architectures and operation conditions of the solar cells. Chapter II, called Experimental, describes different methods and techniques used during this Thesis. The Chapter III is composed of three scientific articles where the results obtained from this Thesis are shown. o Article 1.- "Benign-by-Design Solventless Mechanochemical Synthesis of Three-, Two-, and One-Dimensional Hybrid Perovskites" In this article, the mechano-synthesis is proposed as an alternative method to the preparation of organic-inorganic hybrid perovskites. This method does not use organic solvents (DMSO, DMF) as in traditional perovskite synthesis methods, and therefore it was considered a more benign method to the environment. In addition, this process is fast, simple and reproducible, and capable of obtaining a large amount of polycrystalline powder material with high purity, which considerably facilitates the characterization process. To demonstrate this method, four different perovskites were synthesized, MAPbI3, FAPbI3, GuaPbI3, Gua2PbI4 (MA, FA and Gua are methylammonium, formamidinium and guanidinium, respectively) and were characterized by X-ray diffraction, UV-vis absorption spectroscopy, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Three of these perovskites had been previously synthesized and characterized, but in this work, a guanidinium-based perovskite (GuaPbI3) with a quasi-1D chain structure was synthesized and characterized for the first time. This result is significant in the field of perovskite because it introduces a new method to synthesize new perovskite materials. o Article 2.- “Large guanidinium cation mixed with methylammonium in lead iodide perovskites for 19% efficient solar cells” The perovskites with three-dimensional structures (Chapter 1) present the best optoelectronic properties to be implemented in solar cells but they possess low stability to moisture and oxygen. Thus, the use of guanidinium in mixture with methylammonium was proposed to form an organic multication hybrid perovskite and the insertion of guanidinium within the crystalline network was verified by X-ray diffraction using the Williamson-Hall method (Chapter I). In addition, the increase in the efficiency of the solar cells has been demonstrated using this mixture of cations and an increase of stability in a stress test under constant illumination has been detected (Chapter III). o Article 3.- "Alternative Perovskites for Photovoltaics" The article 3 is a review of the most recent approaches undertaken to explore and implement alternative and innovative perovskite materials in solar cells. These alternatives focus on the overcoming the main limitations of conventional perovskites, including stability and toxicity. In this review, different studies are reported including the substitution of Pb2+ for elements of group 14 such as germanium, removing the problem of toxicity and studies of different cations (methylammonium, rubidium, guanidinium, etc.) to synthesize 2D and quasi-2D perovskites (Ruddlesden-Popper)

Radon Mass Exhalation Rates of Selected Building Materials in Tanzania

This study aimed at determining the mass radon exhalation rate of Tanzania Portland cements and their raw materials for assessment of the radiological hazards due to use of those materials in residential construction. The radon mass exhalation rate was measured by closed chamber coupled with the Pylon AB5 Ô and varied from 0.3 to 13 %. The estimated indoor radon concentrations and annual effective dose for tightly closed standard room were within the safe limits of radon potential health hazards of 600 Bq m-3 for dwellings and 1500 Bq m-3 for workplaces recommended by International Commission on Radiological Protection (ICRP). Key words. Building materials; Radon mass exhalation rate; Annual effective dose; Radiological hazard; Tanzani

Le livre face à la pandémie. Chronique d\u27une crise dans neuf régions françaises.

Avec cet acte III, nous bouclons nos Chroniques d’une crise dans la filière du livre, démarrées avec les effets du confinement du printemps 2020 et poursuivies avec la période de semi-reprise de l’hiver 2020-2021. Et ce, alors qu’une nouvelle vague épidémique submerge le monde, sans empêcher – pour le moment – un presque retour à une vie normale. Même si le soutien financier public a été au rendez-vous, la filière subit encore les conséquences de la crise et s’interroge sur l’avenir : comment vont évoluer les pratiques culturelles des Français, qui se sont résolument tournés vers le numérique à domicile depuis deux ans, tandis que se confirment la baisse du soutien privé pour les manifestations littéraires et la fin du plan de relance pour tous