Metal chalcogenide nanomaterials are interesting due to their size dependent properties and potential use in numerous types of devices or applications. The synthetic methods of binary phase metal chalcogenide nanoparticles are well established, but finding simple ways to make even more complex nanostructures is important. To this end, two techniques were studied: the cation exchange of metal chalcogenide nanocrystals, CdE → MxEy (E = S, Se, Te; M = Pd, Pt) and the solution phase synthesis of ternary chalcogenide nanoparticles. The effects of cation solvation and the volume change (Delta V) of reaction on the equilibrium and the morphology change in the cation-exchange reactions of CdE → MxEy were investigated. A two-phase solvent environment was particularly efficient in increasing the thermodynamic driving force. The effect of Delta V of reaction on the morphology of the product nanocrystals was also investigated. Depending on the stress developed in the lattice during the reaction, product nanocrystals underwent varying degrees of morphological changes, such as void formation and fragmentation, in addition to the preservation of the original morphology of the reactant nanocrystals. The knowledge of the effect of ion solvation and Delta V of reaction on the equilibrium and product morphology provides a new strategy and useful guide to the application of cation-exchange reactions for the synthesis of a broader range of inorganic nanocrystals. Using a solution phase method, the morphology of CuInSe2 nanoparticles could be tuned from small 10 nm spheres to micron length nanowires by varying the relative amount of strong and weak surfactants passivating the surface. Oleylamine and trioctylphosphine oxide were chosen as the strong and weak surfactants, respectively. Small isotropic structures were formed when the oleylamine was the only surfactant with the size of the nanospheres increasing as the amount of oleylamine decreased. For the CuInSe2 nanowires, weakly-binding dioctylphosphine oxide (DOPO), an impurity in the TOPO, was found to be the key surfactant that enables the anisotropic one-dimensional growth. Detailed analysis of the structure of the nanowires indicated that they grow perpendicular to (112) planes, with twinning around the growth axis by ~60 degree rotation. The nanowires exhibit a saw-tooth surface morphology resembling a stack of truncated tetrahedral.

Inexhaustible solar energy, which provides a clean, economic and green energy, seems to be an alternative solution, for current and future energy demands. Harvesting solar energy presents a challenge in using eco-friendly, earth abundant and inexpensive materials. Although present CdTe and Cu (In, Ga)Se2 (CIGS) technologies, provide light-to-electricity comparable to silicon technology, toxicity of Cd and scarcity of In limits the widespread utilization. Future tera-watt level module capacity would then be feasible by the low-cost technologies. The chalcogenide thin film technology would therefore provide the exceptional utilization in the large-area module monolithic integrations benefitting from the low material consumption owing to the direct band gap. The current thesis presents the results obtained from the quest of other thin film materials and their utilization to an unconventional Cd-free buffer layer. The films suitability for the future applications was assessed through photovoltaics device studies in a comparative manner. Chapter-1 deals with the motivation for the solar energy and the importance of thin film photovoltaics. Alternative materials which are abundantly available would help to reach the future tera watt level production, where the conventional silicon technology alone cannot satisfy the global energy demand. The utilization of non-conventional thin film based solar cells and their working principles were elucidated. The histories of the copper based alternative materials were introduced. Chapter-2 deals with the versatile thin film growth technique that has been designed fabricated and installed further which can handle the growth of the absorber and the top TCO layers with insitu sulphurisation. The methodology of the absorber deposition was discussed in detail. The experimental details for the co-sputtering of CuInAl alloy were presented. A novel selenization method, assisted by the combination of inert gases was developed for the annealing of CuInAl alloyed precursor films. Chapter-3 deals with the presentation of the results obtained on buffer and window layers. Chemical Bath deposition technique was employed for the growth and optimization of the conventional CdS and non-toxic buffer ZnS buffer layers. A) Cadmium sulphide thin films suitable for the utilization of high efficiency solar cells were optimized. Optimization of the buffer involved the effects of cadmium precursors, ammonia concentration and buffer capsule effect. A green route was presented so as to consume the precursors to the maximum extent possible. B) The alternative non-toxic buffer Zinc Sulphide (ZnS) thin films were successfully grown using the above optimized conditions. Moreover the window layer was also optimized for better device partner. Zinc Oxide was used as a n-type partner for the p-type CIS films. The ZnO films were grown by the RF-sputtering from the single cathode exhibited good crystallinity with Zincite structure (hexagonal ZnS, a= 3.249A0 and c= 5.205A0). All the grown films showed high resistivity. Al: ZnO thin films were optimized in two methods 1) by dc co-sputtering from the elemental cathodes, Zinc and Aluminum, 2) dc-sputtering from the single 2% Al-doped ZnO cathode. Low resistivity Al:ZnO thin films were deposited in both the cases. Effect of Aluminum doping into ZnO crystal lattice upon the optical and electrical properties were discussed. Chapter-4 deals with the synthesis of various absorber materials, characterizations and some properties. Briefly the A) Optimization of the CuIn1-xAlxSe2 phase with better adhesion and better crystallinity. Aluminum doping into the crystal lattice of CuInSe2 aided the wide band gap tuning of CIAS thin films. Morphological investigations were carried out for the different set of thin films before and after selenization. Effects of copper and Aluminum concentrations on the lattice parameter of the selenized thin films were addressed. The present chapter deals with the A) electrical properties of CIAS films and its heterojunction partners. Resistivity measurements and effects of Cu/In ratio and the effect of Al doping were described in detail. The CIAS/ZnO heterostructure, CIAS/Al:ZnO heterostructure junction properties as a function of different sun illuminations were discussed. B) The alternative earth abundant, eco-friendly, non-toxic elements Cu2ZnSnS4, absorber thin films synthesis and characterizations. Photo conductive photo measurements showed CZTS a potential candidate for near infra-red photodectection. C) Cu2CoSnS4 (CCTS) nanostructures and quantum dots were synthesized via simple chemical routes. CCTS quantum dots were tuned to exhibit the red edge effect and cold white phosphors. D) Cu3BiS3 nano rods were synthesized and characterized structurally and optically. The transport properties of Cu3BiS3 nanorods were tailored for showing the metallic to semiconducting transitions. Chapter-5 Discusses the A) Efforts made in understanding the CIAS based solar cells through interfaces such as CIAS/ZnO, Mo/CIAS, CIAS/CdS/i-ZnO/Al:ZnO and improving the open circuit voltage VOC upon a rotating substrate, involving the inline and in situ processes, for fabricating the cell/ module were discussed. The device statistics for various set of cells were analyzed. B) Solar cells of CTS absorber with the non-toxic buffer ZnS were fabricated and device properties were analyzed. C) CCTS quantum dots embedded in the polymer matrix were utilized for making the inverted hybrid solar devices in combination of ITO/AZnO bilayered contact replacing the acidic PEDOT: PSS. D) The solar cells made of CCTS hollow spheres by spin coating the absorber in the configuration SLG/Mo/CCTS/CdS/ iZno-AZnO/Ni-Al-Al showed a lower efficiency of 0.02%. Chapter-6 concludes with the summary of present investigations and the scope for future work.