Indium tin oxide (ITO) and molybdenum are substrates of choice in the manufacture of the CdS-CIS photovoltaic cell, which is the base for the leading thin-film solar cell technology. Substantial advancement in this technology is expected if these devices can be made in nanoporous alumina (AAO) templates. The first step to this endeavor is to learn to form AAO templates on molybdenum and ITO substrates. This was accomplished, and the results are reported in this thesis. Starting substrates were glass, coated with either a thin molybdenum layer or a thin ITO layer. Aluminum was deposited on top of this conducting substrate. Oxalic acid was used as the electrolyte for anodization. In the case of molybdenum substrates, average pore diameter was 45 nm when an anodization voltage of 40 volts was used for approximately 46 minutes; current density was approximately 23 amps/sq. m. In the case of ITO substrates, pores of 45 nm diameter were obtained for approximately 20 minute anodization at 40 V; current density was 40 amps/sq. m; annealing of aluminum layer prior to anodization, at 550 oC (degrees Centigrade) for 90 minutes was needed to obtain good pores. A one micrometer thick CdS layer was electrodeposited inside the AAO pores on top of the ITO substrate. In preliminary experiments, CdS/Cu2S photovoltaic heterojunctions with an open circuit voltage of 242 mV were formed inside the nanopores.

Nano structured solar cells provide an opportunity for increased open circuit voltages and and short circuit currents in solar cells due to quantum confinement of the window and absorber materials and an increase in the optical path length for the incident light. In this study, both bulk and nano heterojunctions of CIS/CdS and Cu2S/CdS devices have been fabricated and studied on plain glass substrates and inside porous alumina templates to compare their performance. The devices have also been characterized SEM, XRD and JV measurements. The J-V curves have also been analyzed for series resistance, diode ideality factor and reverse saturation current density.

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Silicon nanowires (SiNWs) and the copper chalcogenides, namely copper sulfide (Cu2S) and selenide Cu2Se, have diverse applications in renewable energy technology. For example, SiNWs which have direct band gaps unlike bulk Si, have the potential to radically reduce the cost of Si based photovoltaic cells. However, they degrade quickly under ambient conditions. Various surface passivations have therefore been investigated for enhancing their stability but it is not yet well understood how they affect the electronic structure of SiNWs at a fundamental level. Here, we will explore, from first-principles simulation, how fluorine, methyl and hydrogen surface passivations alter the electronic structures of [111] and [110] SiNWs via strain and quantum confinement. We also show how electronic charge states in [111] and [110] SiNWs can be effectively modelled by simple quantum wells. In addition, we address the issue of why [111] SiNWs are less influenced by their surface passivation than [110] SiNWs. Like SiNWs, Cu2S and Cu2Se also make excellent photovoltaic cells. However, they are most well known for their exceptional thermoelectric performance. This is by virtue of their even more unique solid-liquid hybrid nature which combines the low thermal conductivity and good electrical characteristics required for a high thermoelectric efficiency. We use first-principles molecular dynamics simulations to show that Cu diffusion rates in Cu2S and Cu2Se can be as high as 10-5cm2s-1. We also relate their phonon power spectra to their low thermal conductivities. Furthermore, we evaluate the thermoelectric properties of Cu2S and Cu2Se using a combination of Boltzmann transport theory and first-principles electronic structure calculations. Our results show that both Cu2S and Cu2Se are capable of maintaining high Seebeck coefficients in excess of 200μVK-1 for hole concentrations as high as 3x1020cm-3.