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  Item type:Item, Thesis Access status: Open Access ,

  Febrication and characterization of perovskite solar cells and performance analysis using theoretical study

  (University of North Bengal, 2024) Sarkar, Joy; Chatterjee, Suman

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  In today's world, the demand for energy continues to rise alongside population growth and industrialization. Our reliance on traditional fossil fuels like coal, petroleum, and natural gas has sustained global energy needs but comes at a cost. These finite resources are not only depleting but also contribute significantly to environmental degradation and pose challenges to biodiversity and human health. To ensure a sustainable future, it is imperative to explore renewable energy sources that provide cleaner and more efficient alternatives. Renewable energy, such as solar, wind, tidal waves, geothermal, and biomass, presents viable solutions. These sources harness natural processes that are continuously replenished and have minimal environmental impact compared to fossil fuels. Solar energy, in particular, stands out for its abundant availability and versatility in various applications, from residential rooftops to large-scale solar farms. While conventional silicon-based photovoltaic technologies show promise, their high costs hinder competitiveness with current energy production methods. In contrast, perovskite solar cells represent a novel photovoltaic technology that has attracted significant attention due to promising efficiencies, cost-effectiveness, recyclability, and versatility for diverse applications. Despite the exploration of various PSCs, issues like lead toxicity, stability, and durability have impeded widespread commercial adoption. This thesis aims to advance lead-free perovskite solar cell (PSC) technologies to improve their environmental sustainability, cost-effectiveness, stability, and power conversion efficiency. Organized into eight chapters, this study aims to yield significant advancements in the field, contributing to practical applications and sustainable energy solutions. Chapter 1 explores the current global energy landscape and highlights the urgent need for renewable energy sources. It provides an overview of various types of photovoltaic devices, with a focus on Perovskite Solar Cells. A detailed analysis of the various components of PSCs is presented, including the perovskite absorber layer, electron and hole transport layers, and electrodes. The intricate working mechanisms of PSCs are explained, elucidating how these components interact to convert sunlight into electricity. Additionally, the chapter explores recent advancements and challenges in PSC research. The insights provided in this chapter lay the groundwork for further exploration of PSCs as a promising renewable energy technology. Chapter 2 provides a comprehensive overview of the fundamental theory and detailed descriptions of various experimental techniques used to characterize the materials of the different components of PSCs. These techniques include X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), UV-VIS spectroscopy, Fourier-transform infrared spectroscopy (FTIR), Kelvin probe force microscopy (KPFM), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and photoluminescence (PL) spectroscopy. Additionally, this chapter discusses the principles of current-voltage (I-V) measurement, quantum efficiency (QE) calculations, and electrochemical impedance spectroscopy (EIS), along with a detailed explanation of the critical parameters that determine device performance. In Chapter 3, we provide a comprehensive discussion of the fundamentals of Density Functional Theory (DFT), including the Kohn-Sham theorem. We also address the necessity of using the exchange-correlation functional in the DFT approach. In this work, we employed the WIEN2K software for DFT computations, providing an in-depth discussion of its fundamental operational principles and the various material properties it can accurately calculate. Additionally, we analyze the basic working techniques of the SCAPS-1D simulation tool used to theoretically estimate the performance of PSC devices. Chapter 4 presents a study on improving the photovoltaic performance of lead-free MASnI3-based perovskite solar cells, which uses a mixture of the polar solvent DMSO and activated carbon powder as the counter electrode. The solar cells are fabricated using three different counter-electrode preparation techniques. The device with the DMSO-mixed carbon powder as a counter electrode exhibited the best photovoltaic performance. DMSO was found to improve the carrier production rate at the perovskite surface and strengthen the bonding between perovskite and carbon, leading to enhanced device performance. Finally, the DFT-calculated electronic and optical properties are compared with the experimentally obtained results to validate the key findings. Chapter 5 evaluates the structural, electronic, and optical properties of the lead-free perovskite CsGeIXBr3-X utilizing density functional theory (DFT) calculations. The electronic band gap increased significantly from 1.363 eV to 1.885 eV as the number of Br atoms substituted for I atoms increased. Analysis of the total density of states (TDOS) showed the total electron density in the valence band region increased significantly with Br substitution, reaching a maximum in CsGeBr3. SCAPS-1D device simulations were performed to optimize the performance of perovskite solar cells by adjusting parameters like absorber layer thickness and defect density. The DFT-calculated band gaps and effective density of state values were used to obtain the simulated outcomes. Chapter 6 presents a theoretical investigation of the effect of metal (Cr, Sr, Ag, Cu) doping on the performance of lead-free RbSnI3-based perovskite solar cells. Using density functional theory calculations, the structural and opto-electronic properties of the doped perovskites were measured. The results show that Cu-doped RbSnI3 exhibits the most favorable properties for solar cell applications, including a reduced bandgap, increased dielectric constant, and enhanced charge carrier transport. In addition, SCAPS-1D simulations of the devices based on these doped perovskite materials indicate that the Cu-doped perovskite achieves the highest power conversion efficiency, significantly outperforming the undoped RbSnI3 and other metal-doped counterparts. Chapter 7 focuses on evaluating the performance of lead-free CsSnI3/CsSnBr3 heterostructure-based perovskite solar cells. The surface morphology of the deposited perovskite heterostructure layer was analyzed using SEM and AFM, while EDS and XRD experiments verified sample purity. The optical properties of the heterostructures were characterized using UV-Vis, FTIR, and PL spectroscopy analysis. These analyses revealed the superior suitability of heterostructure perovskites compared to single perovskites for solar cell applications. The current-voltage and EIS results confirm these findings. The analysis of the External Quantum Efficiency (EQE) and Internal Quantum Efficiency (IQE) indicates a significant improvement in the performance of heterostructure-based perovskite solar cells. The surface potential of both the single and heterostructure layers was investigated using KPFM experiments. UPS study was performed to estimate the work function of the perovskite layer. In addition, the study employed both GGA(PBE) and mBJ-LSDA exchange-correlation functionals for DFT computations: GGA for computational efficiency and mBJ-LSDA for accurate band gap and density of states calculation, aligning well with experimental data. The theoretically calculated electronic properties, including the band structure, DOS, and optical characteristics, were thoroughly compared with the experimental outcomes. XPS study was performed to understand the physics behind carrier transport between the absorber layer of the heterostructure perovskite. The results revealed the potential of these lead-free perovskite heterostructures for optoelectronic and photovoltaic applications. The insights gained from this comprehensive study contribute to the understanding of the fundamental properties of these materials and their potential for practical applications in the field of renewable energy. Chapter 8 summarizes the essential findings and conclusions arising from the present work.

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  Item type:Item, Thesis Access status: Open Access ,

  Taxonomic and palynological study of some members of Linderniaceae from Eastern Himalaya and adjoining plains of India

  (University of North Bengal, 2024) Pal, Aaratrik; Chowdhury, Monoranjan

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  Linderniaceae Borsch, Kai Müll. & Eb.Fisch. is a family under Lamiales (APG IV), consisting more than 250 species, under 20 genera and distributed in tropical, subtropical and temperate regions of the world. Members of Linderniaceae are mostly herbs with quadrangular stem, opposite leaves with palmate or pinnate venation, margin entire or, serrate; pedicels in axillary, raceme, or, pseudo-umbel inflorescence; sepals connate; petals bilabiate, perfect stamens 2 or 4, staminodes 0 or 2. In India the family is represented by 56 species under 9 genera. This PhD dissertation was carried out to find out the diversity of different Linderniaceae in the Eastern parts of Indian Himalayan region, and study the taxonomy, nomenclature, systematics, and ecology of those species. This study preliminarily sketches the overall status of Linderniaceae in the Eastern Himalayas. Half of the Indian Linderniaceae grows in the Eastern Himalayas. Total 28 species and seven genera were reported from the studied region, which constitute 50% of the total diversity of Linderniaceae in India. Among the reported species Torenia fournieri is the only cultivated species and used for ornamental purposes. As the elevation of the region ranges from 21 meters to 7,700 to meters, and supports six ecoregions and four biomes, it provides a suitable environment for the diversity of the Linderniaceae plants. Most of the species exhibits preference towards lowland plains, as 21 species and five genera out of the recorded 27 species and five genera occur in Terai-Duar savanna and grasslands ecoregion of the Tropical and Subtropical Grasslands, Savannas and Shrublands biome. The number of species decreases as the altitude rises, and the Eastern Himalayan broadleaf forests ecoregion, ranging from 2,000 to 3,000 meters, supports only six species and three genera. All species except Vandellia montana and V. multiflora, were recorded from multiple locations. These species are less likely to be endangered by anthropogenic or natural threats, as most of the species occur in different types of ecoregions, and are not restricted to any particular type of phytogeographic region. Though, urbanization, along with the decrease in the green spaces, and competition with the invasive alien species threaten their existence. Within much less than five years of span many new records were reported. Among the recorded species, two were described as new species, viz., Bonnaya gracilis and Torenia siliguriensis. B. multiflora and T. concolor were recorded from India for the first time. Lindernia hyssopioides, L. rotundifolia, L. tamilnadensis, and T. godefroyi were recorded from Indian Eastern Himalaya for the first time. Unfortunately, despite the presence of herbarium specimens from the Darjeeling hills, live specimens of Picria fel-terrae could not be located, which might be the result of climate change and habitat destruction. The diversity in the calyx and staminal filaments was documented from the morphological study. Three main types of calyces, viz., five-lobed, connate-tubular, and bi-lipped, were observed. Free calyx lobes were observed in Bonnaya, Lindernia, Picria, Torenia anagallis, Vandellia, and Yamazakia. Connate and tubular calyx was found in Craterostigma and Torenia. Lastly, bi-lipped calyx was exclusive to Torenia s.s. The anterior or the longer pair of filaments have been modified from simple to geniculate-appendaged, geniculate-swollen, or become non-functional as staminodes. Staminodes are restricted to Bonnaya, Lindernia, and Picria. Swollen geniculation is characterized by Craterostigma, Vandellia, and Yamazakia. Finally, appendaged geniculation is limited to Torenia. It also reported the presence of both the seed types in these species, viz., aulacospermous and bothrospermous. Both bayesian inference and maximum likelihood phylogenetic study from the available molecular data (matK) showed congruence with results from the morphological study. This suggested rethinking the phylogenetic position of Vandellia micrantha, V. montana, and V. multiflora. V. micrantha, phylogenetically as well as morphologically, is very distinct from true Vandellia, i.e., V. diffusa. Phylogenetically it’s related to Torenia clade and morphologically also exhibits appendagedgeniculation. V. montana, and V. multiflora on the other hand is morphologically similar to the newly established genus Ymazakia, and is characterized by free calyx lobes equalling ovate-lanceolate capsules. Contrary to this, true Vandellia exhibits partially united calyx lobes, much shorter than the capsule. The matK gene analysis also placed V. montana close to Y. viscosa and Y. pusilla. Therefore, all these morphological as well as molecular affinity suggest new generic treatments for the three, above mentioned species. During nomenclature studies a few nomenclatural as well as typification issues of some Linderniaceae taxa were encountered. Evaluation of nomenclature and taxonomy of Torenia gracilis Benth. revealed that T. gracilis originally not related to Torenia, but to Bonnaya. As T. gracilis was not validly published and T. gracilis was described as a new species of Bonnaya, viz., B. gracilis. One of the key findings was revisiting the nomenclature and taxonomy of Mimilus violaceus Azaola, basionym of Torenia violacea (Azaola) Pennell, to which T. edentula Benth., T. exappendiculata Regel and T. peduncularis Benth. ex Hook.f. was associated as synonyms. It was found that the name M. violaceus was never originally associated with any Torenia, rather the taxonomic identity of M. violaceus is unclear, as no original material except the insufficient description was traced. Besides, no suitable herbarium specimen for T. edentula also could not be located. Therefore, T. edentula was neotypified. Again, as T. violacea is the most used name for the taxon, to which T. edentula is associated, treating T. edentula as the accepted name for the taxon would create nomenclatural instability, so conservation of T. violacea was proposed against T. edentula. Conserved type of M. violaceus and lectotypes of T. exappendiculata and T. peduncularis were also designated. The taxonomic identities of Torenia hians and T. vagans were found to be uncertain, as they have insufficient description for species level identification and the illustrations in their protologue also do not match their descriptions. The synonymy of T. rubens was also resolved. T. rubens has been treated as the synonym of T. concolor, since its first description as a closely related species to T. diffusa. T. rubens was found to be a synonym of T. diffusa. Additionally, lecto-type was designated for T. rubens. Lectotypes of Torenia concolor and T. rubens var. grandiflora was designated, along with the second type lectotypes of T. albomarginata, T. albo-violacea, and T. annamitica. In total one conserved type, one neotype, five lectotype, and three second-type lectotypifications were carried out. Palynological characters of the 16 studied species showed more or less similarities, and are considered as stenopalynos. Pollens were small (rarely medium), tricolpate in these studied species. The investigated quantitative characters of the studied taxa varied in different species and were significant regarding generic level identification. P/E ratio was found highest in Torenia anaglis (1.47) and lowest in L. tamilnadensis (0.84). Pollen shapes also varied from prolate to suboblate. Thinnest exine found in B. ciliata (0.8 μm) whereas T. violacea (1.8 μm) shows thickest exine wall. Overall, though, palynological characters are not sufficient for species identification, but can be used for generic identification. Exine is always more than 1.3 μm in Torenia, and lesser in other three genera. Polar outline is circular in Bonnaya, whereas lobate in Lindernia and triangular in Vandellia. Insects of primarily three orders, namely hymenoptera, lepidoptera, and thysanoptera, were recorded on flowers of three genera and six species of Linderniaceae. These insects were either smaller than the respective visiting corolla or were having very long proboscis. As Linderniaceae has small corolla with tubular opening, these insects were ideal for collecting nectar or pollen.

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  Item type:Item, Thesis Access status: Open Access ,

  Environmental Sustainability and Livelihood Pattern of the Major Tribal People in Jhargram District, West Bengal: A Geographical Study

  (University of North Bengal, 2024) Bera, Ananda Nanda; Roy, Ranjan

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  One of West Bengal's largest districts with a high concentration of tribal people is Jhargram District, India. Measuring the perceived level of the tribal people regarding the natural environment is essential because only this helps us achieve sustainability. Their lives, livelihoods, and living standards solely depend on the environment and natural resources. The perception of tribal people regarding the natural environment and environmental sustainability is one of the key factors in protecting against environmental degradation and maintaining the sustainable livelihood and living standards of tribal people of Jhargram district in particular. This research work is an in-depth study of the environmental sustainability of the Jhargram district and the major tribal communities' patterns of subsistence across the district of Jhargram. In this investigation, the researcher attempted to examine the environmental sustainability and livelihood pattern of the tribal people in Jhargram district with special references to 1) show the spatio-temporal distribution of the major tribes in Jhargram district 2) study the livelihood patterns of the major tribal people in Jhargram district 3) highlight the indigenous knowledge of major tribes for maintaining environmental sustainability in Jhargram district 4) explore the role of environmental sustainability on the livelihood patterns of the major tribal people in Jhargram district and 5) find out the challenges and opportunities of environmental sustainability and livelihood patterns major tribal people in Jhargram district. Jhargram district was created by bifurcating West Medinipur district, and it came into existence on 4th April 2017. The Jhargram district's major tribal communities are the Munda, Santhal, Bhumij, Lodha, Kora, and Mahali tribes. The majority of the tribal people in this area primarily depend on rain-fed agriculture, which is marked by low productivity, erratic weather patterns, low fertility soil, ineffective irrigation, depleted resources, and antiquated methods. The natural environment of the Jhargram district is deeply affected by modern intervention, which is consequently affecting tribal livelihood. With an ex-post-facto research design, the current study used a descriptive crosssectional survey approach. Topographical Maps, Satellite Images, District Planning Series Maps, and so on have been used to describe the physical features of the study area. Programmes like ArcGIS (Version: 10.3.1) and QGIS have been utilised to create the necessary maps. The temporal change in land cover and usage has been assessed using data from remote sensing. Several indices, including the NDVI, NDBI, and multi-criteria decision-making (MCDM) techniques, have been used in this study. To describe the socioeconomic characteristics of the people living in the study area, secondary data has been collected from a variety of sources, including the District Agricultural Annual Plan, District Industrial Profile, District Census Handbook, District Gazetteer, District Statistical Handbook, and data from B.L. & L. R.O. and D.L. & L. R.O. offices. The environmental status of the research region has been described through the collection and analysis of environmental data from the relevant department. Stratified random and purposive sampling techniques have been adopted to collect primary data. Primary data was collected using two types of tools: 1) an interview schedule for important respondents and 2) a semi-structured interview schedule for conducting focus groups with important respondents and in-depth interviews with important respondents such as community leaders and officials at the district and block levels. There are eight chapters throughout the entire work. The problem statement, review of the literature, the gap in the literature, study scope, goal, research questions, database and technique, sample size and design selection, and more are all covered in Chapter I and Chapter II provides an overview of the study area; Chapter III discusses the major tribal population's spatial and temporal distribution; Chapter IV discusses their patterns of livelihood; and Chapter V discusses their use of indigenous knowledge and environmental sustainability; Chapter VI: The Impact of Environmental Sustainability on the Primary Tribal People's Livelihood Patterns; Chapter VII presents the challenges and opportunities of environmental sustainability and livelihood patterns of the major tribal people, and Chapter VIII presents findings, suggestions and conclusions. Different tribal communities are not equally distributed in different blocks in the Jhagram district. The study reveals that most Jhargram district blocks have a healthy sex ratio. The standard of living and quality of life are slightly better than the previous condition. Effect of Modernization and Climatic condition tribal occupation patterns changed. Food habits and religious and cultural practices also changed due to modernization. The percentage of natural and regrowth vegetation cover remaining at 37.44 % (Forest Survey of India, 2022) in Jhargram district is a negative indicator of the health of an ecosystem. This means that the ecosystem cannot provide the many benefits natural vegetation provides, such as clean air and water, fertile soil, and habitat for wildlife. Gain of vegetation Cover -NET % Change in natural vegetation cover over the last five years in Jhargram district is 8.5198 %.

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  Item type:Item, Thesis Access status: Open Access ,

  নাট্যকার বুদ্ধদেব বসু Natyakar Buddhadeb Basu

  (University of North Bengal, 2024) রায় Roy, গোপা Gopa; রায় Roy, নিখিল চন্দ্র Nikhil Chandra

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  Item type:Item, Thesis Access status: Open Access ,

  Urban Transport and Associated Vehicular Emissions in Siliguri City

  (University of North Bengal, 2024) Bose, Arghadeep; Roy Chowdhury, Indrajit

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  The phenomenon of rapid urbanization in contemporary developing nations brings with it a spectrum of challenges and opportunities. Siliguri, a burgeoning metropolitan hub nestled in the foothills of the Himalayas in West Bengal, India, exemplifies this dynamic. Siliguri has risen from a mere village to a significant commercial city. It is a nexus of trade and transportation, holding a strategic geographical and economic position in the region. Its strategic location as a gateway to the northeastern states and neighbouring countries has fuelled its growth, attracted a diverse population, and fostered a bustling economy. However, this rapid growth has not been without its challenges. The city's infrastructure, particularly its road network, has struggled to keep pace with its expanding population, which has grown from 4.72 lakhs in 2001 to 5.13 lakhs in 2011. The roads, characterized by a tangled web of interlinking nodes, serve both the city's internal traffic and intercity movements. Notable roads such as Hill Cart Road, Sevoke Road, and Burdwan Road, while vital, have become synonymous with congestion and environmental stress. The motivation behind this study stems from the pressing need to address the environmental repercussions of urban expansion. The relevance of this research lies in its potential to influence urban planning and policy, ensuring that cities like Siliguri can grow sustainably without compromising environmental integrity or public health. By focusing on the interplay between urban transport systems and associated vehicular emissions, this thesis seeks to unravel the complexities of urbanization and its implications for air quality and urban liveability. The primary objectives of this research encompass a comprehensive analysis of automobile pollution in Siliguri, focusing on quantifying pollutant variations and examining the spatial dynamics of traffic volumes at major intersections. The study aims to explore seasonal fluctuations in pollutant concentrations and investigate the relationship between these pollutants and climatic variables such as temperature and relative humidity. It also seeks to identify the principal causes of traffic congestion in Siliguri and assess the impact of vehicular emissions on human health within the city. Ultimately, the research intends to recommend transport action strategies and legislative measures to effectively reduce the pollution burden in Siliguri, thereby contributing to the development of sustainable urban mobility solutions. To achieve these objectives, a comprehensive database was constructed, encompassing both primary as well as secondary data. A range of methodological approaches was employed across different chapters of the thesis. Spatial analysis techniques, such as Univariate Local Indicators of Spatial Association (LISA) maps and Moran's I statistics, were used to decipher the distribution of pollutants. Structural Equation Modeling (SEM) provided a framework for understanding the health impacts of pollution. Time series models, including ARIMA and TBATS, were applied to forecast the Air Quality Index (AQI) and to predict future trends. The findings of the research are revealing. An in-depth analysis of air pollutants over two years highlighted that the levels of PM2.5 and PM10 were alarmingly high, surpassing national standards and pinpointing traffic volume at key intersections as a significant source. Seasonal variations in pollution were found to be intricately linked with climatic variables, and traffic congestion emerged as a pressing problem, with spatial and temporal disparities across the city. Logistic regression analyses from perception surveys underscored vehicle growth and road space encroachment as primary factors behind peak-hour congestion. The health impact assessments indicated a stark connection between vehicular pollution exposure and adverse health outcomes among residents. This thesis concludes with a clarion call for the implementation of sustainable urban transport and environmental strategies. It underscores the urgency of transitioning research into actionable policies, with a focus on achieving Sustainable Development Goal 11. The study contributes a substantial framework for urban stakeholders, guiding interventions that can reduce pollution levels and enhance quality of life. Through its detailed exploration of Siliguri's urban challenges, the thesis offers an extensive blueprint for other cities grappling with similar issues of urbanization and environmental impact.

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