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This study focuses on William Faulkner, whose works explore the demise of the slavery-based Old South during the Civil War in a highly experimental narrative style. Central to this investigation is the analysis of the temporal dimensions of both individual and collective guilt, thus offering a new approach to the often-discussed problem of Faulkner’s portrayal of social decay. The thesis examines how Faulkner re-narrates the legacy of the Old South as a guilt narrative and argues that Faulkner uses guilt in order to corroborate his concept of time and the idea of the continuity of the past. The focus of the analysis is on three of Faulkner’s arguably most important novels: The Sound and the Fury, Absalom, Absalom!, and Go Down, Moses. Each of these novels features a main character deeply overwhelmed by the crimes of the past, whether private, familial, or societal. As a result, guilt is explored both from a domestic as well as a social perspective. In order to show how Faulkner blends past and present by means of guilt, this work examines several methods and motifs borrowed from different fields and genres with which Faulkner narratively negotiates guilt. These include religious notions of original sin, the motif of the ancestral curse prevalent in the Southern Gothic genre, and the psychological concept of trauma. Each of these motifs emphasizes the temporal dimensions of guilt, which are the core of this study, and makes clear that guilt in Faulkner’s work is primarily to be understood as a temporal rather than a moral problem.
This dissertation examines the integration of incongruent visual-scene and morphological-case information (“cues”) in building thematic-role representations of spoken relative clauses in German.
Addressing the mutual influence of visual and linguistic processing, the Coordinated Interplay Account (CIA) describes a mechanism in two steps supporting visuo-linguistic integration (Knoeferle & Crocker, 2006, Cog Sci). However, the outcomes and dynamics of integrating incongruent thematic-role representations from distinct sources have been investigated scarcely. Further, there is evidence that both second-language (L2) and older speakers may rely on non-syntactic cues relatively more than first-language (L1)/young speakers. Yet, the role of visual information for thematic-role comprehension has not been measured in L2 speakers, and only limitedly across the adult lifespan.
Thematically unambiguous canonically ordered (subject-extracted) and noncanonically ordered (object-extracted) spoken relative clauses in German (see 1a-b) were presented in isolation and alongside visual scenes conveying either the same (congruent) or the opposite (incongruent) thematic relations as the sentence did.
1 a Das ist der Koch, der die Braut verfolgt.
This is the.NOM cook who.NOM the.ACC bride follows
This is the cook who is following the bride.
b Das ist der Koch, den die Braut verfolgt.
This is the.NOM cook whom.ACC the.NOM bride follows
This is the cook whom the bride is following.
The relative contribution of each cue to thematic-role representations was assessed with agent identification. Accuracy and latency data were collected post-sentence from a sample of L1 and L2 speakers (Zona & Felser, 2023), and from a sample of L1 speakers from across the adult lifespan (Zona & Reifegerste, under review). In addition, the moment-by-moment dynamics of thematic-role assignment were investigated with mouse tracking in a young L1 sample (Zona, under review).
The following questions were addressed: (1) How do visual scenes influence thematic-role representations of canonical and noncanonical sentences? (2) How does reliance on visual-scene, case, and word-order cues vary in L1 and L2 speakers? (3) How does reliance on visual-scene, case, and word-order cues change across the lifespan?
The results showed reliable effects of incongruence of visually and linguistically conveyed thematic relations on thematic-role representations. Incongruent (vs. congruent) scenes yielded slower and less accurate responses to agent-identification probes presented post-sentence. The recently inspected agent was considered as the most likely agent ~300ms after trial onset, and the convergence of visual scenes and word order enabled comprehenders to assign thematic roles predictively.
L2 (vs. L1) participants relied more on word order overall. In response to noncanonical clauses presented with incongruent visual scenes, sensitivity to case predicted the size of incongruence effects better than L1-L2 grouping. These results suggest that the individual’s ability to exploit specific cues might predict their weighting.
Sensitivity to case was stable throughout the lifespan, while visual effects increased with increasing age and were modulated by individual interference-inhibition levels. Thus, age-related changes in comprehension may stem from stronger reliance on visually (vs. linguistically) conveyed meaning.
These patterns represent evidence for a recent-role preference – i.e., a tendency to re-assign visually conveyed thematic roles to the same referents in temporally coordinated utterances. The findings (i) extend the generalizability of CIA predictions across stimuli, tasks, populations, and measures of interest, (ii) contribute to specifying the outcomes and mechanisms of detecting and indexing incongruent representations within the CIA, and (iii) speak to current efforts to understand the sources of variability in sentence comprehension.
Open edX is an incredible platform to deliver MOOCs and SPOCs, designed to be robust and support hundreds of thousands of students at the same time. Nevertheless, it lacks a lot of the fine-grained functionality needed to handle students individually in an on-campus course. This short session will present the ongoing project undertaken by the 6 public universities of the Region of Madrid plus the Universitat Politècnica de València, in the framework of a national initiative called UniDigital, funded by the Ministry of Universities of Spain within the Plan de Recuperación, Transformación y Resiliencia of the European Union. This project, led by three of these Spanish universities (UC3M, UPV, UAM), is investing more than half a million euros with the purpose of bringing the Open edX platform closer to the functionalities required for an LMS to support on-campus teaching. The aim of the project is to coordinate what is going to be developed with the Open edX development community, so these developments are incorporated into the core of the Open edX platform in its next releases. Features like a complete redesign of platform analytics to make them real-time, the creation of dashboards based on these analytics, the integration of a system for customized automatic feedback, improvement of exams and tasks and the extension of grading capabilities, improvements in the graphical interfaces for both students and teachers, the extension of the emailing capabilities, redesign of the file management system, integration of H5P content, the integration of a tool to create mind maps, the creation of a system to detect students at risk, or the integration of an advanced voice assistant and a gamification mobile app, among others, are part of the functionalities to be developed. The idea is to transform a first-class MOOC platform into the next on-campus LMS.
Assessing the impact of global change on hydrological systems is one of the greatest hydrological challenges of our time. Changes in land cover, land use, and climate have an impact on water quantity, quality, and temporal availability. There is a widespread consensus that, given the far-reaching effects of global change, hydrological systems can no longer be viewed as static in their structure; instead, they must be regarded as entire ecosystems, wherein hydrological processes interact and coevolve with biological, geomorphological, and pedological processes. To accurately predict the hydrological response under the impact of global change, it is essential to understand this complex coevolution. The knowledge of how hydrological processes, in particular the formation of subsurface (preferential) flow paths, evolve within this coevolution and how they feed back to the other processes is still very limited due to a lack of observational data.
At the hillslope scale, this intertwined system of interactions is known as the hillslope feedback cycle. This thesis aims to enhance our understanding of the hillslope feedback cycle by studying the coevolution of hillslope structure and hillslope hydrological response. Using chronosequences of moraines in two glacial forefields developed from siliceous and calcareous glacial till, the four studies shed light on the complex coevolution of hydrological, biological, and structural hillslope properties, as well as subsurface hydrological flow paths over an evolutionary period of 10 millennia in these two contrasting geologies. The findings indicate that the contrasting properties of siliceous and calcareous parent materials lead
to variations in soil structure, permeability, and water storage. As a result, different plant species and vegetation types are favored on siliceous versus calcareous parent material, leading to diverse ecosystems with distinct hydrological dynamics. The siliceous parent material was found to show a higher activity level in driving the coevolution. The soil pH resulting from parent material weathering emerges as a crucial factor, influencing vegetation development, soil formation, and consequently, hydrology. The acidic weathering of the siliceous parent material favored the accumulation of organic matter, increasing the soils’ water storage capacity and attracting acid-loving shrubs, which further promoted organic matter accumulation and ultimately led to podsolization after 10 000 years. Tracer experiments revealed that the subsurface flow path evolution was influenced by soil and vegetation development, and vice versa. Subsurface flow paths changed from vertical, heterogeneous matrix flow to finger-like flow paths over a few hundred years, evolving into macropore flow, water storage, and lateral subsurface flow after several thousand years. The changes in flow paths among younger age classes were driven by weathering processes altering soil structure, as well as by vegetation development and root activity. In the older age
class, the transition to more water storage and lateral flow was attributed to substantial organic matter accumulation and ongoing podsolization. The rapid vertical water transport in the finger-like flow paths, along with the conductive sandy material, contributed to podsolization and thus to the shift in the hillslope hydrological response.
In contrast, the calcareous site possesses a high pH buffering capacity, creating a neutral to basic environment with relatively low accumulation of dead organic matter, resulting in a lower water storage capacity and the establishment of predominantly grass vegetation. The coevolution was found to be less dynamic over the millennia. Similar to the siliceous site, significant changes in subsurface flow paths occurred between the young age classes. However, unlike the siliceous site, the subsurface flow paths at the calcareous site only altered in shape and not in direction. Tracer experiments showed that flow paths changed from vertical, heterogeneous matrix flow to vertical, finger-like flow paths after a few hundred to thousands of years, which was driven by root activities and weathering processes. Despite having a finer soil texture, water storage at the calcareous site was significantly lower than at the siliceous site, and water transport remained primarily rapid and vertical, contributing to the flourishing of grass vegetation.
The studies elucidated that changes in flow paths are predominantly shaped by the characteristics of the parent material and its weathering products, along with their complex interactions with initial water flow paths and vegetation development. Time, on the other hand, was not found to be a primary factor in describing the evolution of the hydrological response. This thesis makes a valuable contribution to closing the gap in the observations of the coevolution of hydrological processes within the hillslope feedback cycle, which is important to improve predictions of hydrological processes in changing landscapes. Furthermore, it emphasizes the importance of interdisciplinary studies in addressing the hydrological challenges arising from global change.
It is a well-attested finding in head-initial languages that individuals with aphasia (IWA) have greater difficulties in comprehending object-extracted relative clauses (ORCs) as compared to subject-extracted relative clauses (SRCs). Adopting the linguistically based approach of Relativized Minimality (RM; Rizzi, 1990, 2004), the subject-object asymmetry is attributed to the occurrence of a Minimality effect in ORCs due to reduced processing capacities in IWA (Garraffa & Grillo, 2008; Grillo, 2008, 2009). For ORCs, it is claimed that the embedded subject intervenes in the syntactic dependency between the moved object and its trace, resulting in greater processing demands. In contrast, no such intervener is present in SRCs. Based on the theoretical framework of RM and findings from language acquisition (Belletti et al., 2012; Friedmann et al., 2009), it is assumed that Minimality effects are alleviated when the moved object and the intervening subject differ in terms of relevant syntactic features. For German, the language under investigation, the RM approach predicts that number (i.e., singular vs. plural) and the lexical restriction [+NP] feature (i.e., lexically restricted determiner phrases vs. lexically unrestricted pronouns) are considered relevant in the computation of Minimality. Greater degrees of featural distinctiveness are predicted to result in more facilitated processing of ORCs, because IWA can more easily distinguish between the moved object and the intervener.
This cumulative dissertation aims to provide empirical evidence on the validity of the RM approach in accounting for comprehension patterns during relative clause (RC) processing in German-speaking IWA. For that purpose, I conducted two studies including visual-world eye-tracking experiments embedded within an auditory referent-identification task to study the offline and online processing of German RCs. More specifically, target sentences were created to evaluate (a) whether IWA demonstrate a subject-object asymmetry, (b) whether dissimilarity in the number and/or the [+NP] features facilitates ORC processing, and (c) whether sentence processing in IWA benefits from greater degrees of featural distinctiveness. Furthermore, by comparing RCs disambiguated through case marking (at the relative pronoun or the following noun phrase) and number marking (inflection of the sentence-final verb), it was possible to consider the role of the relative position of the disambiguation point. The RM approach predicts that dissimilarity in case should not affect the occurrence of Minimality effects. However, the case cue to sentence interpretation appears earlier within RCs than the number cue, which may result in lower processing costs in case-disambiguated RCs compared to number-disambiguated RCs.
In study I, target sentences varied with respect to word order (SRC vs. ORC) and dissimilarity in the [+NP] feature (lexically restricted determiner phrase vs. pronouns as embedded element). Moreover, by comparing the impact of these manipulations in case- and number-disambiguated RCs, the effect of dissimilarity in the number feature was explored. IWA demonstrated a subject-object asymmetry, indicating the occurrence of a Minimality effect in ORCs. However, dissimilarity neither in the number feature nor in the [+NP] feature alone facilitated ORC processing. Instead, only ORCs involving distinct specifications of both the number and the [+NP] features were well comprehended by IWA. In study II, only temporarily ambiguous ORCs disambiguated through case or number marking were investigated, while controlling for varying points of disambiguation. There was a slight processing advantage of case marking as cue to sentence interpretation as compared to number marking.
Taken together, these findings suggest that the RM approach can only partially capture empirical data from German IWA. In processing complex syntactic structures, IWA are susceptible to the occurrence of the intervening subject in ORCs. The new findings reported in the thesis show that structural dissimilarity can modulate sentence comprehension in aphasia. Interestingly, IWA can override Minimality effects in ORCs and derive correct sentence meaning if the featural specifications of the constituents are maximally different, because they can more easily distinguish the moved object and the intervening subject given their reduced processing capacities. This dissertation presents new scientific knowledge that highlights how the syntactic theory of RM helps to uncover selective effects of morpho-syntactic features on sentence comprehension in aphasia, emphasizing the close link between assumptions from theoretical syntax and empirical research.
It is a common finding that preschoolers have difficulties in identifying who is doing what to whom in non-canonical sentences, such as (object-verb-subject) OVS and passive sentences in German. This dissertation investigates how German monolingual and German-Italian simultaneous bilingual children process German OVS sentences in Study 1 and German passives in Study 2. Offline data (i.e., accuracy data) and online data (i.e., eye-gaze and pupillometry data) were analyzed to explore whether children can assign thematic roles during sentence comprehension and processing. Executive functions, language-internal and -external factors were investigated as potential predictors for children’s sentence comprehension and processing.
Throughout the literature, there are contradicting findings on the relation between language and executive functions. While some results show a bilingual cognitive advantage over monolingual speakers, others suggest there is no relationship between bilingualism and executive functions. If bilingual children possess more advanced executive function abilities than monolingual children, then this might also be reflected in a better performance on linguistic tasks. In the current studies monolingual and bilingual children were tested by means of two executive function tasks: the Flanker task and the task-switching paradigm. However, these findings showed no bilingual cognitive advantages and no better performance by bilingual children in the linguistic tasks. The performance was rather comparable between bilingual and monolingual children, or even better for the monolingual group. This may be due to cross-linguistic influences and language experience (i.e., language input and output). Italian was used because it does not syntactically overlap with the structure of German OVS sentences, and it only overlapped with one of the two types of sentence condition used for the passive study - considering the subject-(finite)verb alignment. The findings showed a better performance of bilingual children in the passive sentence structure that syntactically overlapped in the two languages, providing evidence for cross-linguistic influences.
Further factors for children’s sentence comprehension were considered. The parents’ education, the number of older siblings and language experience variables were derived from a language background questionnaire completed by parents. Scores of receptive vocabulary and grammar, visual and short-term memory and reasoning ability were measured by means of standardized tests. It was shown that higher German language experience by bilinguals correlates with better accuracy in German OVS sentences but not in passive sentences. Memory capacity had a positive effect on the comprehension of OVS and passive sentences in the bilingual group. Additionally, a role was played by executive function abilities in the comprehension of OVS sentences and not of passive sentences. It is suggested that executive function abilities might help children in the sentence comprehension task when the linguistic structures are not yet fully mastered.
Altogether, these findings show that bilinguals’ poorer performance in the comprehension and processing of German OVS is mainly due to reduced language experience in German, and that the different performance of bilingual children with the two types of passives is mainly due to cross-linguistic influences.
The increasing number of known exoplanets raises questions about their demographics and the mechanisms that shape planets into how we observe them today. Young planets in close-in orbits are exposed to harsh environments due to the host star being magnetically highly active, which results in high X-ray and extreme UV fluxes impinging on the planet. Prolonged exposure to this intense photoionizing radiation can cause planetary atmospheres to heat up, expand and escape into space via a hydrodynamic escape process known as photoevaporation. For super-Earth and sub-Neptune-type planets, this can even lead to the complete erosion of their primordial gaseous atmospheres. A factor of interest for this particular mass-loss process is the activity evolution of the host star. Stellar rotation, which drives the dynamo and with it the magnetic activity of a star, changes significantly over the stellar lifetime. This strongly affects the amount of high-energy radiation received by a planet as stars age. At a young age, planets still host warm and extended envelopes, making them particularly susceptible to atmospheric evaporation. Especially in the first gigayear, when X-ray and UV levels can be 100 - 10,000 times higher than for the present-day sun, the characteristics of the host star and the detailed evolution of its high-energy emission are of importance.
In this thesis, I study the impact of stellar activity evolution on the high-energy-induced atmospheric mass loss of young exoplanets. The PLATYPOS code was developed as part of this thesis to calculate photoevaporative mass-loss rates over time. The code, which couples parameterized planetary mass-radius relations with an analytical hydrodynamic escape model, was used, together with Chandra and eROSITA X-ray observations, to investigate the future mass loss of the two young multiplanet systems V1298 Tau and K2-198. Further, in a numerical ensemble study, the effect of a realistic spread of activity tracks on the small-planet radius gap was investigated for the first time. The works in this thesis show that for individual systems, in particular if planetary masses are unconstrained, the difference between a young host star following a low-activity track vs. a high-activity one can have major implications: the exact shape of the activity evolution can determine whether a planet can hold on to some of its atmosphere, or completely loses its envelope, leaving only the bare rocky core behind. For an ensemble of simulated planets, an observationally-motivated distribution of activity tracks does not substantially change the final radius distribution at ages of several gigayears. My simulations indicate that the overall shape and slope of the resulting small-planet radius gap is not significantly affected by the spread in stellar activity tracks. However, it can account for a certain scattering or fuzziness observed in and around the radius gap of the observed exoplanet population.
Protected cultivation in greenhouses or polytunnels offers the potential for sustainable production of high-yield, high-quality vegetables. This is related to the ability to produce more on less land and to use resources responsibly and efficiently. Crop yield has long been considered the most important factor. However, as plant-based diets have been proposed for a sustainable food system, the targeted enrichment of health-promoting plant secondary metabolites should be addressed. These metabolites include carotenoids and flavonoids, which are associated with several health benefits, such as cardiovascular health and cancer protection.
Cover materials generally have an influence on the climatic conditions, which in turn can affect the levels of secondary metabolites in vegetables grown underneath. Plastic materials are cost-effective and their properties can be modified by incorporating additives, making them the first choice. However, these additives can migrate and leach from the material, resulting in reduced service life, increased waste and possible environmental release. Antifogging additives are used in agricultural films to prevent the formation of droplets on the film surface, thereby increasing light transmission and preventing microbiological contamination.
This thesis focuses on LDPE/EVA covers and incorporated antifogging additives for sustainable protected cultivation, following two different approaches. The first addressed the direct effects of leached antifogging additives using simulation studies on lettuce leaves (Lactuca sativa var capitata L). The second determined the effect of antifog polytunnel covers on lettuce quality. Lettuce is usually grown under protective cover and can provide high nutritional value due to its carotenoid and flavonoid content, depending on the cultivar.
To study the influence of simulated leached antifogging additives on lettuce leaves, a GC-MS method was first developed to analyze these additives based on their fatty acid moieties. Three structurally different antifogging additives (reference material) were characterized outside of a polymer matrix for the first time. All of them contained more than the main fatty acid specified by the manufacturer. Furthermore, they were found to adhere to the leaf surface and could not be removed by water or partially by hexane.
The incorporation of these additives into polytunnel covers affects carotenoid levels in lettuce, but not flavonoids, caffeic acid derivatives and chlorophylls. Specifically, carotenoids were higher in lettuce grown under polytunnels without antifog than with antifog. This has been linked to their effect on the light regime and was suggested to be related to carotenoid function in photosynthesis.
In terms of protected cultivation, the use of LDPE/EVA polytunnels affected light and temperature, and both are closely related. The carotenoid and flavonoid contents of lettuce grown under polytunnels was reversed, with higher carotenoid and lower flavonoid levels. At the individual level, the flavonoids detected in lettuce did not differ however, lettuce carotenoids adapted specifically depending on the time of cultivation. Flavonoid reduction was shown to be transcriptionally regulated (CHS) in response to UV light (UVR8). In contrast, carotenoids are thought to be regulated post-transcriptionally, as indicated by the lack of correlation between carotenoid levels and transcripts of the first enzyme in carotenoid biosynthesis (PSY) and a carotenoid degrading enzyme (CCD4), as well as the increased carotenoid metabolic flux. Understanding the regulatory mechanisms and metabolite adaptation strategies could further advance the strategic development and selection of cover materials.
Nils-Hendrik Grohmann beschäftigt sich mit dem noch andauernden Stärkungsprozess der UN-Menschenrechtsvertragsorgane. Er analysiert, welche rechtlichen Befugnisse die Ausschüsse haben, ob sie von sich aus Vorschläge einbringen können und inwieweit sie ihre Verfahrensweisen bisher aufeinander abgestimmt haben. Ein weiterer Schwerpunkt liegt auf der Zusammenarbeit zwischen den verschiedenen Ausschüssen und der Frage, welche Rolle das Treffen der Vorsitzenden bei der Stärkung spielen kann.
Global warming, driven primarily by the excessive emission of greenhouse gases such as carbon dioxide into the atmosphere, has led to severe and detrimental environmental impacts. Rising global temperatures have triggered a cascade of adverse effects, including melting glaciers and polar ice caps, more frequent and intense heat waves disrupted weather patterns, and the acidification of oceans. These changes adversely affect ecosystems, biodiversity, and human societies, threatening food security, water availability, and livelihoods. One promising solution to mitigate the harmful effects of global warming is the widespread adoption of solar cells, also known as photovoltaic cells. Solar cells harness sunlight to generate electricity without emitting greenhouse gases or other pollutants. By replacing fossil fuel-based energy sources, solar cells can significantly reduce CO2 emissions, a significant contributor to global warming. This transition to clean, renewable energy can help curb the increasing concentration of greenhouse gases in the atmosphere, thereby slowing down the rate of global temperature rise.
Solar energy’s positive impact extends beyond emission reduction. As solar panels become more efficient and affordable, they empower individuals, communities, and even entire nations to generate electricity and become less dependent on fossil fuels. This decentralized energy generation can enhance resilience in the face of climate-related challenges. Moreover, implementing solar cells creates green jobs and stimulates technological innovation, further promoting sustainable economic growth. As solar technology advances, its integration with energy storage systems and smart grids can ensure a stable and reliable energy supply, reducing the need for backup fossil fuel power plants that exacerbate environmental degradation.
The market-dominant solar cell technology is silicon-based, highly matured technology with a highly systematic production procedure. However, it suffers from several drawbacks, such as: 1) Cost: still relatively high due to high energy consumption due to the need to melt and purify silicon, and the use of silver as an electrode, which hinders their widespread availability, especially in low-income countries. 2) Efficiency: theoretically, it should deliver around 29%; however, the efficiency of most of the commercially available silicon-based solar cells ranges from 18 – 22%. 3) Temperature sensitivity: The efficiency decreases with the increase in the temperature, affecting their output. 4) Resource constraints: silicon as a raw material is unavailable in all countries, creating supply chain challenges.
Perovskite solar cells arose in 2011 and matured very rapidly in the last decade as a highly efficient and versatile solar cell technology. With an efficiency of 26%, high absorption coefficients, solution processability, and tunable band gap, it attracted the attention of the solar cells community. It represented a hope for cheap, efficient, and easily processable next-generation solar cells. However, lead toxicity might be the block stone hindering perovskite solar cells’ market reach. Lead is a heavy and bioavailable element that makes perovskite solar cells environmentally unfriendly technology. As a result, scientists try to replace lead with a more environmentally friendly element. Among several possible alternatives, tin was the most suitable element due to its electronic and atomic structure similarity to lead.
Tin perovskites were developed to alleviate the challenge of lead toxicity. Theoretically, it shows very high absorption coefficients, an optimum band gap of 1.35 eV for FASnI3, and a very high short circuit current, which nominates it to deliver the highest possible efficiency of a single junction solar cell, which is around 30.1% according to Schockly-Quisser limit. However, tin perovskites’ efficiency still lags below 15% and is irreproducible, especially from lab to lab. This humble performance could be attributed to three reasons: 1) Tin (II) oxidation to tin (IV), which would happen due to oxygen, water, or even by the effect of the solvent, as was discovered recently. 2) fast crystallization dynamics, which occurs due to the lateral exposure of the P-orbitals of the tin atom, which enhances its reactivity and increases the crystallization pace. 3) Energy band misalignment: The energy bands at the interfaces between the perovskite absorber material and the charge selective layers are not aligned, leading to high interfacial charge recombination, which devastates the photovoltaic performance. To solve these issues, we implemented several techniques and approaches that enhanced the efficiency of tin halide perovskites, providing new chemically safe solvents and antisolvents. In addition, we studied the energy band alignment between the charge transport layers and the tin perovskite absorber.
Recent research has shown that the principal source of tin oxidation is the solvent known as dimethylsulfoxide, which also happens to be one of the most effective solvents for processing perovskite. The search for a stable solvent might prove to be the factor that makes all the difference in the stability of tin-based perovskites. We started with a database of over 2,000 solvents and narrowed it down to a series of 12 new solvents that are suitable for processing FASnI3 experimentally. This was accomplished by looking into 1) the solubility of the precursor chemicals FAI and SnI2, 2) the thermal stability of the precursor solution, and 3) the potential to form perovskite. Finally, we show that it is possible to manufacture solar cells using a novel solvent system that outperforms those produced using DMSO. The results of our research give some suggestions that may be used in the search for novel solvents or mixes of solvents that can be used to manufacture stable tin-based perovskites.
Due to the quick crystallization of tin, it is more difficult to deposit tin-based perovskite films from a solution than manufacturing lead-based perovskite films since lead perovskite is more often utilized. The most efficient way to get high efficiencies is to deposit perovskite from dimethyl sulfoxide (DMSO), which slows down the quick construction of the tin-iodine network that is responsible for perovskite synthesis. This is the most successful approach for achieving high efficiencies. Dimethyl sulfoxide, which is used in the processing, is responsible for the oxidation of tin, which is a disadvantage of this method. This research presents a potentially fruitful alternative in which 4-(tert-butyl) pyridine can substitute dimethyl sulfoxide in the process of regulating crystallization without causing tin oxidation to take place. Perovskite films that have been formed from pyridine have been shown to have a much-reduced defect density. This has resulted in increased charge mobility and better photovoltaic performance, making pyridine a desirable alternative for use in the deposition of tin perovskite films.
The precise control of perovskite precursor crystallization inside a thin film is of utmost importance for optimizing the efficiency and manufacturing of solar cells. The deposition process of tin-based perovskite films from a solution presents difficulties due to the quick crystallization of tin compared to the more often employed lead perovskite. The optimal approach for attaining elevated efficiencies entails using dimethyl sulfoxide (DMSO) as a medium for depositing perovskite. This choice of solvent impedes the tin-iodine network’s fast aggregation, which plays a crucial role in the production of perovskite. Nevertheless, this methodology is limited since the utilization of dimethyl sulfoxide leads to the oxidation of tin throughout the processing stage. In this thesis, we present a potentially advantageous alternative approach wherein 4-(tert-butyl) pyridine is proposed as a substitute for dimethyl sulfoxide in regulating crystallization processes while avoiding the undesired consequence of tin oxidation. Films of perovskite formed using pyridine as a solvent have a notably reduced density of defects, resulting in higher mobility of charges and improved performance in solar applications. Consequently, the utilization of pyridine for the deposition of tin perovskite films is considered advantageous.
Tin perovskites are suffering from an apparent energy band misalignment. However, the band diagrams published in the current body of research display contradictions, resulting in a dearth of unanimity. Moreover, comprehensive information about the dynamics connected with charge extraction is lacking. This thesis aims to ascertain the energy band locations of tin perovskites by employing the kelvin probe and Photoelectron yield spectroscopy methods. This thesis aims to construct a precise band diagram for the often-utilized device stack. Moreover, a comprehensive analysis is performed to assess the energy deficits inherent in the current energetic structure of tin halide perovskites. In addition, we investigate the influence of BCP on the improvement of electron extraction in C60/BCP systems, with a specific emphasis on the energy factors involved. Furthermore, transient surface photovoltage was utilized to investigate the charge extraction kinetics of frequently studied charge transport layers, such as NiOx and PEDOT as hole transport layers and C60, ICBA, and PCBM as electron transport layers. The Hall effect, KP, and TRPL approaches accurately ascertain the p-doping concentration in FASnI3. The results consistently demonstrated a value of 1.5 * 1017 cm-3. Our research findings highlight the imperative nature of autonomously constructing the charge extraction layers for tin halide perovskites, apart from those used for lead perovskites.
The crystallization of perovskite precursors relies mainly on the utilization of two solvents. The first one dissolves the perovskite powder to form the precursor solution, usually called the solvent. The second one precipitates the perovskite precursor, forming the wet film, which is a supersaturated solution of perovskite precursor and in the remains of the solvent and the antisolvent. Later, this wet film crystallizes upon annealing into a full perovskite crystallized film. In our research context, we proposed new solvents to dissolve FASnI3, but when we tried to form a film, most of them did not crystallize. This is attributed to the high coordination strength between the metal halide and the solvent molecules, which is unbreakable by the traditionally used antisolvents such as Toluene and Chlorobenzene. To solve this issue, we introduce a high-throughput antisolvent screening in which we screened around 73 selected antisolvents against 15 solvents that can form a 1M FASnI3 solution. We used for the first time in tin perovskites machine learning algorithm to understand and predict the effect of an antisolvent on the crystallization of a precursor solution in a particular solvent. We relied on film darkness as a primary criterion to judge the efficacy of a solvent-antisolvent pair. We found that the relative polarity between solvent and antisolvent is the primary factor that affects the solvent-antisolvent interaction. Based on our findings, we prepared several high-quality tin perovskite films free from DMSO and achieved an efficiency of 9%, which is the highest DMSO tin perovskite device so far.