Opto-electronic properties of 3D nanostructures for use in high efficient solar cell applications

By removing the aluminum threads, we will be able to resume a new nano structure that has the potential to absorb more light in a solar cell. To remove the aluminum nano wires, we use a wet-etch technique. During this process we have developed a method for measuring the residues of aluminum in the structure. These structures can potentially increase the efficiency of solar cells by getting more power out, and also reducing the cost of introducing a direct band-gap material. In addition, these structures can potentially be used in sensors, membranes, batteries, and thermoelectric elements that make electrical current of heat. The focus of the project has been to create and optimize the nanostructures, study how the self-organizing process starts and develops, and investigate the optical properties of the wires on the nanoscale. For these observations, we use state-of-the-art instruments, such as the newly installed transmission electron microscope within the NORTEM project, co-financed by the Norwegian Research Council. These studies are combined with studies on optical and electrical properties to understand their properties and the possible applications for which they can be used. In addition, we have worked to understand and develop the properties of the material around the nanowires. When adding small amounts of aluminum and hydrogen to this material (amorphous silicon), we have observed changes of the optical properties of the material.

The self-organizing nanostructures presented in the Nanosol project represent a completely novel way of thinking device fabrication. The possibilities for materials tailoring by manipulating nanowires are already vast and can be found in material systems other than Si-Al, opening for a whole new branch of materials design. Both the nanostructures aSi, aSi-Al films, and the tunable aSi (doped with Al and/or H) has shown to exhibit interesting optoelectronic properties. These could have significant potential to be used in optoelectronic devices, sensors, memory storage materials etc. We have during this project gained competence within nanofabrication and characterization of nanostructures for optoelectronic devices.

The NanoSol project will study the fundamental aspects of nanowires and nanoholes, self-organization and growth, plasmonics, and nano-confinement of opto-electronic properties, measured both on the micro- and nano-scale. Inexpensive 3-dimensional nanostru ctured materials will be produced in a novel way, using magnetron co-sputtering to form Al nanowires in amorphous Si. Our approach presents a completely new concept of self-organizing Si based structures for device applications, which have never been repo rted and used so far. The scientific interest of the project is threefold: The self-organization phenomenon observed for this system is in itself an intriguing issue triggering various enquiries. The plasmonic properties of the Al nanowires or nanoholes, as well as the opto-electronic properties of the wires and holes measured on the micro- and nano-scale, will give insight into the detailed properties, method possibilities, and possible applications. The possibility of materials tailoring offered by thes e Si based nanostructures widens the fabrication options for a broad range of potential devices, which require careful process development and materials characterization and testing. Semiconductor nanostructures consisting of wires, tubes, particles, and thin films have shown to have unique electrical and optical properties compared to their bulk counterpart. In this context these nanostructures are very interesting candidates to be used in various devices, for instance in photovoltaic devices, sensors, t hermoelectric devices, and batteries. One of the advantages associated with the NanoSol proposed concept over presently used technologies is the fact that the nanostructures are grown at room temperature without the use of precursors, which has been reali zed at our SINTEF laboratories, to our knowledge for the first time. These processing characteristics offer the competitive advantages of cost-effectiveness and simplicity, both crucial from a commercial perspective