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.

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