Alternative Energy Harvesting and Conversion Systems Based on Nanostructured Heterostructures

Abstract: Conversion and storage of the solar radiation into applicable forms of energy, using ubiquitous materials is of central importance that quests several disciplinary fields in both applied technology and fundamental science. Harnessing the solar energy received by the earth has the potential to replace the current sources of energy and it is imperative for sustainable development. Since the early development of modern photovoltaics (PVs), based on silicon wafers, a rational step was the substantial development of the new generation PV technologies that can provide lower-cost and higher efficiency than their predecessors. Deliberate solutions involved employing different semiconducting materials that are indispensable, non-toxic and compatible with large-scale fabricating technologies.  Exploiting metal oxide (MOx) semiconductors, a broad class of non-toxic, cheap and abundant materials, is already promoted as a key component for high-performance optoelectronic devices and can be an ideal solution for inexpensive harnessing of sustainable energy resources like Sun light. The favorable band gap and high absorption cross-section of some MOx semiconductors permit utilizing different spectral region of the solar spectrum. However, at this present, the implication of MOx in high-throughput optoelectronic devices remained on the low side. Some of the main drawbacks that attain to poor performance of the MOx are associated with their poor intrinsic carrier mobility especially in p-type light absorbers and insufficient visible light absorption notably in n-type semiconductors.   The main aim of this thesis is to further contribute to the development and exploitation of this class of materials with the main focus on their role in optoelectronic devices and energy storage systems. The content of this thesis considers two main aspect of the research. Substantially, this work analyses the vital role of the interface engineering using nanostructured MOx, where we exploit unique phenomena such as intense electric field confinement in 1dimensional (1D) structures resulting in ample light trapping in the fabricated heterojunctions. Unfortunately, this fact comes at the cost of introducing space charge region (SCR) limits in the fabricated devices attaining for poor derived currents. Here I would probably spend couple of words for introducing the Co3O4 NR as the basis for p-n inverted nanorod junction…Plasmonic metal nanoparticles (NPs) were conventionally used to extend the spectral response of the wide-bandgap semiconductors. Within the scheme of this thesis, we employ the silver plasmonic NPs in a 1D light harvesting structure of zinc oxide (ZnO), where we mediate hot-carrier collection of the charges via controlled illuminations. Even further, we provide a comprehensive analysis on the hot-carrier redistribution mechanisms of the plasmonic NPs to semiconductor, providing direct experimental proof using transient pump-probe spectroscopy and time-resolved photoluminescence analysis. Our work resulted in a distinct understanding of the radiative and non-radiative carrier transfer between the active constituents of the system, which have not been corroborated previously.In a parallel approach, the research activities in this work, take a few steps ahead and investigates the issues related to the disparities in the PV plants. A common prerequisite after conversion of the solar light using PV devices is the electrochemical storage of the energy where it can answer the needs for far-reaching energy requirements. Fostered by the intrinsic capacitance characteristic of the MOx, we interplay the role of the interfacial engineering in Co3O4 porous films and investigate the effect of their lateral architecture on Li+ ion adsorption and desorption properties.Finally, our findings resulted in the fabrication of a hybrid device with dual functionality as an all-oxide PV system that can directly store the converted Sunlight as in a supercapacitor device. The prospect of this device can provide the over-potential required for direct storage of the converted solar energy into larger high storage systems.In summary, the results presented in this thesis highlights the potential of the MOx semiconductors for photovoltaic and storage applications. We identify the various step-forward routes, which can provide the possibility of large-scale deployment of this novel class of materials.