Interdisciplinary Centre for Energy Research (ICER)
https://etd.iisc.ac.in/handle/2005/28
2024-03-28T15:13:35ZAdvances in Architecturing of Large-Scale Photovoltaics: Packaging and Incidence Angle Agnostic Hierarchical Nanostructures
https://etd.iisc.ac.in/handle/2005/6297
Advances in Architecturing of Large-Scale Photovoltaics: Packaging and Incidence Angle Agnostic Hierarchical Nanostructures
Adiga, Varun
Encapsulant of Graphene embedded polymer that exhibits low permeability to moisture and oxygen were used as a packaging material for OPVDs. Graphene-Surlyn encapsulated and unencapsulated devices were stored both in ambient and inert conditions to evaluate the performance of the encapsulant material. The devices with encapsulation and stored inside the glove box exhibited 88% of the initial performance after more than 50000 hours of real-time ageing. These results demonstrate an enormous increase in the lifetime of the devices, paving the
way for robust and long-life OPV devices.
Hierarchically nanostructured coatings (HNC), crucial for adequate light trapping and enhancing the capacity of silicon solar cells to convert light into energy, provide the potential for better photon management. To absorb light from virtually any angle, an effort is made to emulate the biomimetic design of a particular type of insect. We coated the HNC to polycrystalline silicon solar cells (epoxy) using a thermosetting polymer and the PDMS stamping technique. The hierarchically built solar cell outperformed solar cells made of bare silicon by around 25% in terms of power production at a maximum angle of incidence of 41.53°.
The hierarchically formed solar cell might replace the demand for tracking-based
solar panels. Superior optoelectronic properties are embraced by this self-assembled HNC method
for a range of solar cell applications. The HNC on silicon solar cells was performed on larger (1m
x 2m) panels to assess the scalability of these structures. The performance improvement of the
panels was ~80% of that of the small-scale version, with ~20% enhancement in the cumulative
power generation throughout the day.
To tune the optical losses caused by refractive index mismatch and spectrum conversion from the IR to the visible area, which can be a potential rival in silicon photovoltaics, this work has included both HNC and up-conversion material (NaYF4:Yb/Er). Infrared light absorbers and green, blue, and red light emitters are two functions of the rare-earth-doped up-conversion nanoparticles employed in this thesis. When subjected to constant IR irradiation for 15 days, the integration of NaYF4:Yb/Er up-conversion nanoparticles decreased the temperature of the cells by a margin of around 20%. A 32% increase in power output over reference solar cells was also discovered.
Correlation between Morphology, Microstructure and Corrosion Behaviour of Nickel-Phosphorous (Ni-P) Based Electrodeposited Coatings
https://etd.iisc.ac.in/handle/2005/6039
Correlation between Morphology, Microstructure and Corrosion Behaviour of Nickel-Phosphorous (Ni-P) Based Electrodeposited Coatings
Meshram, Atul P
The Ni-P alloy coatings are widely studied due to their superior mechanical and tribological properties. Ni-P coatings are also considered to be a viable alternative to the chromium (Cr) coatings which utilize environmentally hazardous and toxic carcinogenic electrolytic solutions. The current work focuses on strategies to enhance the corrosion resistance performance of electrodeposited Ni-P coatings primarily by incorporation of foreign additives (carbon nanotubes (CNTs) and graphene) and by engineering of the Ni-P micro-texture and phase fraction (crystalline and amorphous phases). Nickel-phosphorus (Ni-P) coatings were electrodeposited over mild steel substrate using DC power source in conventional two electrode electrochemical setup. As-deposited Ni-P coatings were subjected to phase, microstructural and morphological characterizations using x-ray diffraction, electron microscopy and electron backscatter diffraction techniques. The corrosion analysis was accomplished by using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarisation techniques (Tafel plot) in 3.5 wt.% NaCl solution. Key observations are: (a) in the work on the incorporation of CNTs and Graphene in Ni-P coatings, it was observed that an optimum volume fraction of the additives yielded high corrosion resistance performance. This was essentially due to the smooth compact and defect free surface morphology, (b) in the work on the correlation between micro-texture and corrosion behaviour of Ni-P coatings as a function of phosphorous content, it was observed that the phosphorous concentration range where the nano-crystalline region (along with the minor amorphous phase fraction) was dominant a slight alteration in texture determines the corrosion rate. With increase in the amorphous region, the galvanic coupling between the anodic amorphous phase and cathodic crystalline phase determined the corrosion behaviour. A mixture of amorphous and crystalline phases with lower fraction of the amorphous phase enhanced the corrosion rate due to increased galvanic coupling. For higher addition of phosphorus, large fraction of amorphous phase evolved which significantly reduced the galvanic coupling leading to higher corrosion resistance behaviour, (c) in the work on the effect of deposition temperature (bath temperature of 15˚C, 20˚C, 25˚C, 35˚C) on the evolution of correlation between texture and corrosion behaviour of Ni-P coatings, it was observed that the coating deposited at 15°C and 25°C yielded the maximum and minimum corrosion rate respectively. Analysis of the coating texture revealed that the higher corrosion rate for the 15°C coating was due to low fraction of low energy low angle grain boundaries (LAGBs), higher strain within the grains, and (101) growth texture. Lower corrosion rate, on the other hand, for the 25°C coating was due to low energy (001) growth texture, low average strain within the grains, and high fraction of LAGBs, (d) in the work on the effect of deposition current density on the evolution of correlation between texture and corrosion behaviour of Ni-P coatings, it was observed that the Ni-P coating (deposited using 60 mA.cm-2) that exhibited the lowest corrosion rate was characterized by the presence of lower energy surface texture, lower grain size, narrow grain size distribution and a relatively higher fraction of low energy Σ3 coherent twin boundaries. A higher corrosion rate for coating deposited using 5 mA.cm-2 was due to higher energy surface texture and larger grain size distribution.
Cryomilled Group IV elements (Silicon & Germanium) for optoelectronic applications
https://etd.iisc.ac.in/handle/2005/5473
Cryomilled Group IV elements (Silicon & Germanium) for optoelectronic applications
Hemaprabha, E
Group IV elements such as silicon and germanium are elemental semiconductors and lead to the evolution of modern electronic applications. Synthesis of contamination-free nanoparticles of these materials in bulk quantity becomes an important aspect because the contaminations could substantially change the electrical properties. With this in motivation, the thesis is focused on synthesis of nanoparticles of Si and Ge by cryomilling. Following this we have explored the optoelectronic applications. Thesis is organized in eight chapters and a brief description of each chapter is given here. Chapter 1 introduces the research topic and briefly explains the work performed in this thesis. Chapter 2 provides the literature review on synthesis methods of Si nanostructures. Chapter 3 explains the experimental methods used to synthesize Si and Ge nanoparticles and process methods to fabricate optoelectronic devices. Chapter 4 presents our work on the synthesis of Si nanoparticles by cryomilling. Cryomilling is a type of ball milling in which the powders are milled at cryogenic temperature to avoid the inadvertent reactions, which has been used in this work to synthesis Si and Ge nanoparticles. The dynamics of the ball motion during the cryomilling process has been understood for the efficient synthesis of nanoparticles. Initially, p-type and n-type Si nanoparticles have been synthesized by the cryomilling process. The phase and structural characterizations reveal the polycrystalline particles containing both amorphous and crystalline grains. One-step simple etching process has been proposed to obtain the nanocrystals. Photoluminescence studies of this nanocrystals show the luminescence at UV range, and the efficiency has been estimated. The particles were functionalized to enhance the colloidal and oxidation stability. In chapter 5, the optimized synthesis parameters of Si have been employed on germanium to obtain nano crystals, which belongs to the same group (group IV). Ge ink has been further synthesized using functionalization process. In chapter 6, the application of doped Si nanoparticles has been explored by incorporating the particles in organic-inorganic hybrid solar cells. The device efficiency has been improved, and the effect of various dopant states on device performance has been studied. Solution-processed semiconductors are promising candidates for next-generation optoelectronic devices. In chapter 7, spray coating and inkjet printing methods are used to fabricate semiconducting diodes using Si and Ge nanoparticles. Si nanocrystals obtained from the etching process have been sandwiched in TiO2/CuI semiconductor device using a spray coating process. The reason behind the improved current flow in the diode, due to the addition of Si nanocrystals and the mechanism has been explored. Ge ink obtained from the functionalization step has been inkjet printed on Si to obtain Si-Ge heterostructure. The major problem of coffee-stain effect during the inkjet printing has been suppressed, and the current- voltage characteristics of the device showed the diode behavior. Chapter 8 summarizes the thesis work and explains the future scope of the thesis
Density Stratified Thermal Energy Storage System and Associated Fluid Dynamic Perturbations
https://etd.iisc.ac.in/handle/2005/4411
Density Stratified Thermal Energy Storage System and Associated Fluid Dynamic Perturbations
Advaith, S
The hunger of humankind for energy has reached unprecedented levels with the ever-rising industrialization and global population surge. We are witnessing a global economic evolution towards a clean, affordable, sustainable and reliable sources of energy which could transform our lives and the planet itself. The mismatch between the supply of solar energy which is one among the most promising renewable energy and the demand for its utilization, compel us to incorporate a solar energy storage. Such storage systems are essential in various fields including power generation sectors like power plants based on solar thermal, thermal (non-renewable) and nuclear.
The study is primarily an experimental investigation of single tank sensible stratified thermal energy storage which sheds light on the experimental procedure to establish a stable and sustainable thermocline thermal energy storage. Moreover, in order to have an understanding of the causes of capacity loss in such stratified storage tanks, various studies are conducted, both numerically as well as experimentally. The performance of the TES depends on the integrity of the temperature gradient region (thermocline thickness). Mixing and spatio-temporal perturbations at the thermocline region is the foremost cause of capacity loss and the most important mechanism which destroys the stratification is vortex/plume entrainment in a thermocline-based storage tank. In a stably stratified TES, vortex entrainment occurs when a relatively cold mass of fluid is injected into the tank. Vortex-thermocline interaction creates vortices by baroclinicity, leading to entrainment and mixing. Hence any vortex entrainment in the thermocline region is critical and determines the efficiency of such thermal storage.
Density stratification formed in terms of salinity as an analogy to that due to temperature as well as the effect of disturbances are studied. As a corollary, various distributors are compared numerically and tested the advantage of a novel distributor design. The work provides quality experimental data in order to meet with its inadequacy in the related literature as well as deeper understanding into the establishment of a stable and sustainable thermocline thermal energy storage