Thesis (M.S.)--Boston University. PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / Efficient and economical photoanodes used in photoelectrochemical cells (PEC) to produce hydrogen gas by water decomposition using sunlight must both absorb a large portion of incident solar radiation and be stable in alkaline or acidic electrolytic solutions. While smaller bandgaps are necessary to efficiently absorb visible light, only large bandgap materials that absorb primarily UV radiation are known to be stable in photoelectrochemical cells. A promising method of increasing the absorption of photoanodes while retaining corrosion resistance is to create heterostructured materials that feature a low-bandgap material encapsulated by a corrosion-resistant metal oxide layer. In this work, two methods of fabricating heterostructured photoanodes through electrospray deposition of particles and post-deposition sintering were investigated. In the first method, layered photoanodes were fabricated using a needle-to-plane electrode geometry. A layer of low-bandgap TiSi2 particles was deposited onto a titanium substrate followed by a second layer of TiO2 nanoparticles. The structure was then sintered at 600◦C for 3 hours to promote TiSi2 interparticle necks and TiO2 densification. In the second method, sintered core-shell particles were produced using a novel three-electrode electrospray mixing device consisting of two opposing, oppositely energized hypodermic needle electrodes and a planar ground electrode. The core-shell structure was verified by encapsulating larger, 2.92μm polystyrene latex spheres with smaller 0.96μm spheres and examining the structure under an optical [TRUNCATED]

Anthropogenic climate change presents an unrivalled threat to environmental stability and the prosperity of future generations. Utilising abundant, renewable resources in energy generation and storage will be essential to halt climate change and its effects. Solar water splitting is an excellent tool in the renewable energy arsenal for countering climate change, as it utilises both sunlight and water, two of the most abundant resources available on earth. Furthermore, the direct formation of a chemical fuel, hydrogen, is thought to be more practical for storing in large quantities than electricity. Work in this thesis covers the investigation of a variety of materials, fabricated by aerosol assisted chemical vapour deposition (AACVD), for their ability to carry out photoelectrochemical water splitting. In one project, thin films of Bi2Ti2O7 (BTO), specifically of the pyrochlore crystal structure, are fabricated by AACVD and analysed for their photoelectrochemical properties. The resulting thin films are found to be phase pure with a band gap of 2.88 eV, which is 0.32 eV smaller than TiO2. Efforts to dope the BTO thin films are further investigated through the addition of iron. Significant modification to the band gap is observed, leading to a confirmed pyrochlore thin film exhibiting a band gap of 2.5 eV, a reduction of 0.38 eV from undoped BTO. The resulting thin film had a photocurrent 5 times higher than that of undoped BTO. Finally, efforts to fabricate Fe2Ti2O7 are outlined. It is discovered that a stable phase of Fe2TiO5 is preferentially formed over the pyrochlore phase, even with dramatic modification to the deposition parameters and precursor stoichiometry. The high stability of this phase, coupled with the limiting features of the glass substrates, highlights the challenges with forming certain pyrochlore thin films. In a second project, the effect of depositing titanium nanoclusters onto the surface of bismuth vanadate is investigated. Nanoclusters are of huge interest because their properties lie between those of atoms and bulk materials. Additionally, nanoscale clusters can be fabricated with incredible precision, allowing one to select discrete diameter particles for deposition on surfaces. Ti nanoclusters over a range of sizes are deposited onto BiVO4 photoanodes. It is discovered that the deposition of ultralow loadings of Ti2000 clusters results in an 80 % enhancement in the photocurrent of the BiVO4 substrates. Further experimentation highlights that the photocurrent enhancement is linked to the size of the nanocluster and the density of the clusters on the surface. A mechanism is outlined, whereby the Ti nanoclusters partially reduce the surface of the BiVO4, leading to enhanced electron transport within the thin films due to the presence of oxygen vacancies. In a final project, polycrystalline InN, GaN and systematically controlled InxGa1-xN composite thin films are fabricated on FTO glass by a facile, low-cost and scalable aerosol assisted chemical vapor deposition technique. Variation of the indium content in the composite films leads to a dramatic shift in the optical absorbance properties, which correlates with the band edges shifting between those of GaN to InN. Moreover, the photoelectrochemical properties are shown to vary with indium content, with the 50 % indium composite having an external quantum efficiency of around 8 %. Whilst the overall photocurrent is found to be low, the photocurrent stability is shown to be excellent, with little degradation seen over 1 hour. Subsequent attempts to modify the morphology by conducting vertical-AACVD are also outlined. Thin films fabricated using vertical-AACVD are found to grow via a different mechanism, leading to undesired split phase growth, where two different compositions form on the same substrate.

La séparation photoélectrochimique de l'eau (PEC) est un moyen direct de produire un combustible solaire tel que l'hydrogène à partir de l'eau. Le goulot d'étranglement de ce processus se situe dans la photoanode, qui est responsable du côté oxydation de la réaction1,2. Dans ce travail, l'utilisation de BiVO4 en tant que photoanode a été largement étudiée afin d'améliorer sa photoactivité. L’optimisation de la synthèse de photoanodes BiVO4 par électrodéposition en couche mince sur du FTO a été réalisée. Les facteurs influant sur l'activité photoélectrochimique, tels que le temps d'électrodéposition, le rapport Bi-KI/benzoquinone-EtOH dans le bain de dépôt et la température de calcination, ont été étudiés à l'aide de la conception composite centrale d'expériences. Les états de surface sur la surface de BiVO4 donnent lieu à des niveaux de défaut pouvant induire une recombinaison électron-trou via le mécanisme de Shockley-Read-Hall5. Afin de minimiser les inefficacités dues à la recombinaison électron-trou et passiver les états de surface, des couches de recouvrement ultra-fines d'Al2O3 et de TiO2 ont été déposées sur les électrodes en film mince BiVO4 d'une manière analogue à l'ALD. Cela a également été réalisé afin de protéger la surface de BiVO4 de la photocorrosion et d’augmenter sa stabilité. Une densité de photocourant de 0,54 mA/cm2 à 1,23 V vs RHE a été obtenue pour les 2 cycles de BiVO4 modifié par Al2O3, comme le montre la Figure 2, soit une amélioration de 54% par rapport à la BiVO4 nue qui démontrait une densité de photocourant de 0,35 mA/cm2. à 1,23 V vs RHE. Une augmentation de 15% de la stabilité de l'électrode de BiVO4 modifiée par Al2O3 a également été observée au cours de 7,5 heures d'irradiation continue. De plus, grâce aux mesures de capacité de surface présentées à la Figure 3, il a été montré que la surcouche de Al2O3 passivait effectivement à passiver les états de surface des électrodes de BiVO4. La nature de la surface de BiVO4 a été étudiée en étudiant la réactivité de la poudre de BiVO4 avec un titrant chimique. L’existence de groupes hydroxyle de surface sur BiVO4 a été confirmée et quantifiée (max. 1,5 OH / nm2) par titrage chimique. La réaction de la poudre de BiVO4 avec une impulsion de AlMe3 et une impulsion de H2O a montré qu'il existait 1,2 molécules de CH4 dégagées par Bi-OH. Dans ce travail, nous avons pu mettre en évidence les facteurs importants dans la synthèse de BiVO4 et leur incidence sur la photoactivité résultante. Nous avons également réussi à passiver les états de surface de BiVO4 en utilisant Al2O3, ce qui n’est pas bien exploré dans la littérature. De plus, nous avons pu sonder et discuter de la nature de la surface de BiVO4. Ceci est une connaissance très fondamentale et le premier rapport à ce sujet, à notre connaissance. Une bonne compréhension de cette surface semi-conductrice importante et de ses interactions facilitera la conception d'un photoanode BiVO4 plus efficace / Photoelectrochemical (PEC) water splitting is a direct way of producing a solar fuel like hydrogen from water. The bottleneck of this process is in the photoanode, which is responsible for the water oxidation side of the reaction1,2. In this work, the use of BiVO4 as a photoanode was extensively studied in order to improve its photoactivity. The optimization of BiVO4 photoanode synthesis via thin film electrodeposition on FTO was performed. The factors affecting the photoelectrochemical activity such as the electrodeposition time, ratio of the Bi-KI to benzoquinone-EtOH in the deposition bath, and the calcination temperature, have been investigated by using the Central Composite Design of Experiments.Surface states on the BiVO4 surface give rise to defect levels, which can mediate electron-hole recombination via the Shockley-Read-Hall mechanism5. In order to protect the BiVO4 surface and minimize the inefficiencies due to electron-hole recombination and passivate the surface states, ultrathin overlayers of Al2O3 and TiO2 were deposited to the BiVO4 thin film electrodes in an ALD-like manner. A photocurrent density of 0.54 mA/cm2 at 1.23 V vs RHE was obtained for the 2 cycles Al2O3-modified BiVO4, which was a 54% improvement from the bare BiVO4 that demonstrated a photocurrent density of 0.35 mA/cm2 at 1.23 V vs RHE. A 15% increase in stability of the Al2O3- modified BiVO4 electrode was also observed over 7.5 hours of continuous irradiation. Moreover, through surface capacitance measurements, it was shown that the Al2O3 overlayer was indeed passivating the surface states of the BiVO4 electrodes. The nature of the BiVO4 surface was studied by investigating the reactivity of powder BiVO4 with a chemical titrant. The existence of surface hydroxyl groups on BiVO4 was confirmed and quantified (max 1.5 OH/nm2) via chemical titration. The reaction of the BiVO4 powder with one pulse of AlMe3 and 1 pulse of H2O showed that there were 1.2 molecules of CH4 evolved per Bi-OH. In this work, we were able to highlight which factors are important in the synthesis of BiVO4, and how they affect the resulting photoactivity. We have also achieved the passivation of the BiVO4 surface states using Al2O3, which is not well-explored in literature. Moreover, we were able to probe and discuss the nature of the BiVO4 surface. This is a very fundamental knowledge and the first report of such, to the best of our knowledge. A good understanding of this important semiconductor surface and its interactions will aid in the design of a more efficient BiVO4 photoanode

Orientador: Prof. Dr. Flavio Leandro de Souza / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Nanociências e Materiais Avançados, 2017. / Titanato de estrôncio é um material semicondutor interessante para aplicação em células fotoeletroquímicas. Uma via simples e de baixo custo para a preparação de fotoeletrodos de titanato de estrôncio é o método sol-gel. O método complexo polimerizado permite um controle ótimo da estequiometria e da incorporação de dopantes durante o processo. Neste trabalho, fotoanodos de titanato de estrôncio puro e dopado foram preparados usando o método sol-gel. Em primeiro lugar, fotoanodos de titanato de estrôncio puro foram produzidos e tratados termicamente a 800 °C. Em seguida, incorporaram-se os dopantes de ítrio (Y2+) e níquel (Ni2+), sendo realizado uma otimização de deposição para alcançar o melhor desempenho fotoeletroquímico. Além disso, avaliou-se a influência de um tratamento térmico em diferentes condições atmosféricas (nitrogênio e oxigênio) nas propriedades fotoeletroquímicas. Todos os fotoanodos foram analisados estruturalmente, morfologicamente e eletro/fotoeletroquimicamente. As deposições de 6 camadas e 4 tratamentos térmicos de puros e dopados, exibiram a melhor performance analisada por voltametria de varredura linear. Destacou-se os fotoanodos dopados com ítrio, apresentando a maior fotocorrente, comparado com o puro e o dopado com níquel. Adicionalmente, foram analisadas as contribuições na atividade catalítica favorecida pelo tratamento térmica adicional de 15 minutos em atmosfera rica e deficiente em oxigênio. Observou-se que o desempenho aumentou para o material puro submetido a um tratamento térmico adicional em atmosfera de oxigênio e para material dopado com ítrio e submetido a tratamento em atmosfera de nitrogênio. No entanto, fotoanodos de titanato de estrônico, nas diferentes condições de síntese e atmosfera de tratamento térmico, apresentam o desempenho fotoeletroquímico baixo. Em primeiro lugar, o intervalo de banda de titanato de estrôncio puro é muito elevado, 3,2 eV, que permite absorver uma pequena faixa do espectro da radiação solar. Por fim, sugere-se que a maior parte dos dopantes podem estar segregando nos contornos, podendo atuar como centros de recombinação, que reduz a eficiência das reações de superfície. Finalmente, os fotoanodos foram analisados eletroquimicamente através de espectroscopia impedância eletroquímica (EIS) para analisar os possíveis limitantes na performance do material. / Strontium titanate is an interesting semiconductor to be applied in photoelectrochemical cells. A simple and cost effective route to prepare strontium titanate photoelectrode is the sol-gel method. The polymerized complex method allows an optimal control of stoichiometry and the incorporation of impurities during the process. In this work, pure and doped strontium titanate photoanodes were prepared by using sol-gel method. Firstly, pure strontium titanate films were produced and heat treated at 800¿aC. Then, yttrium (Y2+) and nickel (Ni2+) dopants were incorporated. It was made a deposition optimization in order to achieve the best photoelectrochemical performance. Additionally, it was evaluated the influence of an extra heat treatment at different atmosphere (nitrogen and oxygen) on photoanodes properties. All the photoanodes were analyzed structurally, morphologically and electro/photoelectrochemically. Pure and doped strontium titanate photoanodes with 6 layer depositions and 4 time heat treatments exhibited best photocurrent than other conditions provided by linear sweep voltammetry. Yttrium-doped exhibited best photocurrent than pure and nickel-doped strontium titanate. Finally, catalytic activity of pure strontium titanate with extra heat treatment for 15 minutes in oxygen atmosphere and yttrium-doped strontium titanate with extra heat treatment for 15 minutes in nitrogen atmosphere was increased. Nevertheless, photocurrent performances of pure and modified strontium titanate films under air, nitrogen, oxygen atmosphere was very poor which can be explained by plausible hypothesis. Firstly, the band gap of pure strontium titanate is very high ¡V 3.2 eV. So, It only absorbs UV light which is only 4% of sun light. Secondly, most of the dopants may be segregated which may act as recombination centers that reduced the charge separation efficiency. Finally, polaron size of pure and doped strontium titanate under extra oxygen atmosphere decreases. Thus, resistance to charge transfer increases. Under extra nitrogen atmosphere, recombination may have increased as these films exhibited higher conductivity than films prepared under oxygen atmosphere.

This diploma thesis deals with a plasmochemical treatment of photoanodes with an active layer containing TiO2 deposited on two different substrates by material printing. The plasmochemical treatment was performed by a low-temperature ambient-air plasma using a diffuse coplanar surface barrier discharge (DCSBD). The experimental part is focused on the investigation of DCSBD influence on the fabricated photoanodes photoelectrochemical properties, and the influence of plasma treatment time. Process optimization was achieved by height adjustment of the electrode. The processed coatings were electrochemically investigated by linear sweep voltammetry and chronoamperometry.

Water pollution has become an environmental catastrophe due to the rapid urbanization. The treatment of dumping of waste chemicals in water bodies has contributed to the increase in pollution. In addition to the pollution caused by waste chemicals, faecal bacteria such as Escherichia, Staphylococcus, Pseudomonas etc., can cause serious health issues. Techniques such as filtration and chlorination provide clean water but are associated with disadvantages such as toxic by-products. Although clean water can be still obtained by these techniques, the development of resistance by microorganisms with such conventional treatments of antibiotics is inevitable and poses a new threat. Various researches have taken place in the past few decades to provide clean drinking water. Photocatalysis is considered to be a promising viable alternative for the existing methods to solve the menace of water pollution. It is an advanced oxidation process where the reactive oxygen species are generated by using nanomaterials that can cause degradation of chemicals and pathogens. Particularly, photocatalysis using semiconductors and their composites have been tested for their use in the destruction of contaminants. Several methods have been used in the synthesis of nanomaterials and the variations in their morphologies have resulted in different applications such as photocatalysis and electrocatalysis. Among all semiconductors, TiO2 has been widely used in this application owing to their non-toxicity and abundance in availability. However, TiO2 can be activated only in the presence of UV light. Therefore, the formation of heterojunctions, doping of metals/no- metals in TiO2 has enabled the activation of TiO2 in the visible region. The former approach has also been studied with ceria and silver salts combination. Besides conventional metal oxides, other transitional metal oxides such as copper oxide and bismuth oxide have also been studied owing to its conducting property and facile growth on substrates respectively for enhanced photocatalysis. All the above tweaking has enabled efficient charge separation, band gap reduction, and prevention of recombination. In this thesis, all the nanomaterials and their composites have been synthesized using simple methods such as solution combustion, hydrothermal, solution co-precipitation, and chemical deposition. The primary aim of this thesis is to synthesize various effective nanomaterials with different morphologies, bandgap engineered nanocomposites, metal or non-metal doped metal oxides for efficient waste water treatment of dyes, antibiotics, phenols, and bacteria. Besides, relying on photocatalytic ability, the photoconductivity and intrinsic conducting properties of nanomaterials were exploited to perform photoelectrocatalysis that enhances the rate of decontamination to several orders than photocatalysis. In addition to focusing on increasing the rate of degradation, the main drawback of photocatalysis which is catalyst retrieval has been overcome using conducting substrates and nanomaterial coated substrates for efficient photocatalytic and photoelectrocatalytic decontamination of waste water. All the structural, morphological, chemical and optical properties were thoroughly studied using various characterization techniques such as XRD, SEM, TEM, XPS, UV-DRS, PL respectively. The rate kinetics of dye, antibiotic and phenol degradation was examined. Experimental data was tested with the proposed model in the case of photoelectrocatalytic degradation. The photocatalysts were also studied for its reusability for many cycles. All the proposed works have analyzed the reason for the enhanced activity by performing scavenger reactions to determine the responsible reactive oxygen species. Thus, this thesis exhibits a thorough understanding of how to design and engineer nanomaterials for photocatalytic and photoelectrocatalytic water remediation. The following are the chapters discussed in this thesis. Chapter 1 discusses the drawbacks associated with the current waste water treatment methods and the possibilities of photocatalysis to replace the existing treatments. The advantages of certain transition metals, conventional methods of synthesis and various other properties of the nanomaterials have been discussed. Chapter 2 explains the synthesis of TiO2 nanobelts using combustion synthesized TiO2 under UV and solar irradiation. The catalyst has been characterized for its structural, morphological, chemical and optical properties. The degradation of anionic and cationic dyes and their activity against E.coli bacteria have been evaluated. The efficiency of this catalyst has been compared with commercial Degussa P25. This study shows the morphological influence of nanomaterials on photocatalytic activity. Chapter 3 describes the synthesis of Ag3PO4 impregnated combustion synthesized TiO2 nanobelts using co-precipitation technique. The activity of this material has been studied under solar light. The catalyst has been characterized for its structural, morphological, chemical and optical properties. Similar to the previous chapter, the degradation of dyes and the antibacterial activity of this catalyst has been compared with commercial Degussa P25. This study explains the importance of morphology and charge carrier facilitation in the case of heterojunction formation. Chapter 4 explains the synthesis of ceria nanoflakes by solution combustion method using ascorbic acid as fuel and PEG assisted sonochemical method. The catalyst has been characterized for its structural, morphological, chemical and optical properties. The effect of silver salts such as AgBr on ceria/Ag3PO4 under visible region for degradation of dyes and antibacterial activity has been evaluated. This work elucidates the effect of band engineering in the charge carrier dynamics between interfaces of components within the catalysts. Chapter 5 elucidates the synthesis of vanadium, nitrogen co doped TiO2 catalysts for the simultaneous degradation of microbes and antibiotics. The primary aim of this work is to understand whether interstitial or substituted doped nitrogen will be effective in the presence of vanadium. The photoactivity of this novel catalyst was studied for its synergistic degradation of antibiotics and bacteria simultaneously towards the prevention of microbial resistance towards antibiotics. Chloramphenicol and E.coli were subjected to photodegradation under visible light. Chapter 6 explains the synthesis of copper oxide based nanomaterial for antibiotic and bacterial degradation by photoelectrocatalysis. In order to enhance the rate of photodegradation, photocatalysis has been upgraded with the application of a potential to photocatalytic systems that possess better charge conducting capability. Highly network like copper oxide has been synthesized using conventional combustion synthesis method and compared with copper oxide nanorods synthesized by hydrothermal method. The rate kinetics of photocatalytic and photoelectrocatalytic degradation of antibiotics has been examined thoroughly and validated based on a cyclic network model. This work demonstrates the synergistic rate enhancing capacity upon combining photocatalysis and electrocatalysis. Chapter 7 discusses the fabrication of Cu/CuO/FTO (fluorine doped tin oxide) based substrates for bacterial degradation. Considering the difficulties in photocatalyst retrieval processes and realizing the importance of electrocatalysis, conducting substrates such as Cu strip, FTO were subjected to antibacterial treatment. Formation of copper oxide onto copper strip during the course of reaction forced us to develop CuO/Cu and CuO/FTO interfaces to examine the photocatalytic and photoelectrocatalytic killing of E.coli. Chapter 8 investigates the fabrication of Bi2O3/Ag based material for photocatalytic and photoelectrocatalytic degradation for phenols and substituted phenols. This work starts with fabrication of Bi2O3 working electrodes by chemical deposition. Photodegradation experiments were conducted under UV irradiation and enhancement of the rate of degradation was observed when the working electrode was deposited with silver nanoparticles via chemical reduction method. Formation of the intermediate Bi(OH)x on Bi2O3 or Bi2O3/Ag has resulted in better hydroxyl radical generation upon excitation. Similarly, surface plasmon resonance due to silver nanoparticles was found to be responsible for augmentation in degradation efficiency of phenol. Chapter 9 briefly summarizes the work and provides future directions. The research work thus attempts to design and engineer photocatalytic nanomaterials that are better than the existing materials and emphasizes the importance towards water remediation.

Titania has been the focus of attention for several decades owing to its chemical stability, non-toxicity, inexpensiveness and robust surface chemistry. Its technological applications include use in diverse areas such as photocatalytic reactors, antibacterial coatings, dye sensitive solar cells (DSSC) and more recently the perovskite solar cells to name a few. All of these applications are based on the ability to inject or generate electronhole pairs in titania and transport them to a suitable interface at which they are ejected to either engender a reaction as in photocatalysis or drive a load as in photovoltaics. From a technological perspective it is also important that such science be achieved and controlled in supported titania structures. The research reported in this thesis, thus, started with the development of a process for obtaining adherent titania films by oxidation of sputtered Ti films on stainless steel, a very commonly used substrate. Challenges that had to be overcome included the need to oxidize titanium to obtain the right phase mixture while preventing film cracking or delamination due to compressive stresses generated during anodic oxidation of Ti. During this process of obtaining nanostructured TiO2 through anodization, it was serendipitously discovered that planar TiO2 films obtained by oxidation of sputtered Ti films did significantly better than anodized nanoporous titania in bactericidal studies. This was then replicated in organic dye degradation studies. Analysis of the material showed that this improved performance was due to the unintentional contamination during sputtering by Cu, Zn, Mo possibly due to arcing across brass contacts. This quaternary system was then systematically explored and it was shown that an optimal metastable composition in the Ti- Cu-Mo oxide ternary system performs the best. DFT studies showed that this was due to introduction of shallow and deep states in the band gap that, depending on the level of dopants, either enhances carrier lifetimes or leads to recombination. In continuation of this work on supported titania structures by oxidation of Ti, a novel photoanode for use in dye sensitized photovoltaics was developed by oxidation of Ti foam. This results in an interconnected 3-D network of TiO2 that possess at its core a network of Ti. Such architecture was designed to provide a large surface area for anchoring the sensitizer while simultaneously reducing the distance that charge carriers have to travel before reaching the ohmic contacts to prevent recombination losses. The thesis discusses the preparation of such anodes, the properties of the 3-D oxide and cells, with up to 4% efficiency, developed using such anodes. Reasons for such behaviour and avenues for further exploration to improve cell efficiency will also be discussed.

The photo-conversion efficiency and stability of back-illuminated dye sensitised solar cells with titanium foil based photoanodes are enhanced by a simple nitric acid treatment through which the foil is passivated. This treatment changes the morphology of the titanium foil and increases its electrochemical double layer capacitance.

Dye-sensitized solar cells (DSC) have attracted considerable scientific and industrial interest during the past decade as an economically feasible alternative to conventional photovoltaic devices. DSCs have the potential to be as efficient as silicon solar cells, but at a fraction of the cost of silicon solar cells. The unique advantage of DSC compared to conventional solar cells is that the light absorption, electron transport and hole transport are handled by different components which reduces the chance of recombination. In the present work, to facilitate DSC with good energy conversion efficiency, its performance have been evaluated as a function of titania layer morphology, redox couple concentration and the catalytic layer on the counter electrode. The results that are obtained in the present investigations have been organized as follows Chapter 1 gives a brief exposure to DSC technology. Special emphasize has been on the structure and individual components of the DSC. Chapter 2 describes various experimental techniques that are employed to fabricate and characterize DSCs under study. Chapter 3 presents a systematic study of the characteristics of DSC made of three different types of electrodes namely: TiO2 nanotubes (TNT) which have excellent electron transport properties, TiO2 microspheres (TMS) which possess high surface area and light scattering ability and TiO2 nano particles (TNP) possessing high surface area. The electronic, morphological, optical and surface properties of individual electrodes are studied. The highest efficiency of 8.03% is obtained for DSCs prepared with TMS electrodes. A higher value of effective diffusion coefficient (Deff) and diffusion length (Ln) of electrons as obtained by electrochemical impedance spectroscopy (EIS) analysis confirms a high charge collection efficiency in microsphere based cell. Chapter 4 gives a detailed study of DSCs fabricated with a tri-layer photo anode with TNTs as light scattering layer. The tri-layer structure has given an enhanced efficiency of 7.15% which is 16% higher than TNP based cell and 40% higher than TNT based cells. Chapter 5 deals with the investigations on the effect of concentration of redox couple on the photovoltaic properties of DSC for different ratios of [I2] to [LiI] (1:2, 1:5 and 1:10) with five viii concentrations of I2 namely 0.01 M, 0.03 M, 0.05 M, 0.08 M and 0.1M in acetonitrile. It is found that the open circuit potential (Voc) decreases with increase in the ratio of redox couple whereas short circuit current density (Jsc) and fill factor (FF) increase. The reason for the decline in Voc is the higher recombination between electrons in the conduction band of TiO2 and the I3- ions present in the electrolyte, induced by the absorptive Li+ ions. In addition using EIS it is found that the τ improves with the increase in [LiI] at a particular [I2], whereas at a fixed [I2]/ [LiI] ratio the increase in [I2] is found to reduce the τ and Deff due to the enhanced recombination. Chapter 6 describes the application of carbon based counter electrode (CE) materials for DSCs. Two counter electrode materials have been investigated namely (1) Multiwalled carbon nanotubes (MWCNT) synthesized by pyrolysis method and (2) Platinum decorated multiwalled carbon nanotubes (Pt/MWCNT) prepared by chemical reduction of platinum precursors. Using Pt/MWCNT composite electrode the DSC achieved an energy conversion efficiency of 6.5 %. From the analysis on symmetric cells, it is found that electro catalytic activity of Pt/MWCNT CE is similar to that of platinum CE, though the platinum loading is very less for the former. This is attributed to the effective utilization of catalyst owing to high surface area arising from the increased surface roughness. Chapter 7 discusses the application of titanium foil in place of glass substrate for the photo anode. The titanium foil offers fabrication of flexible DSC. The performance of DSC with TMS layers and aligned titania nanotube arrays (TNA) prepared by anodization method is studied. Compared to TMS based cell, TNA has given a better efficiency at a lower thickness. Chapter 8 presents the scheme used to seal DSCs and its stability analysis. We have employed the usual hot melt sealing for edge whereas hole sealing is carried out with tooth pick and a UV curable adhesive. The degradation in efficiency is found to be 20% for low efficiency cells whereas, for high efficiency cells it is found to be 45% after 45 days. The leakage of highly volatile acetonitrile through the edge and hole is found to be responsible for the reduction in the performance of the device. Hence a high temperature sealing method is proposed to fabricate stable cells. Chapter 9 gives summary and conclusions of the present work