Functionalization of conducting oxides by ion beam and defect engineering

One of the most central challenges facing our common global future is access to sufficient supply of clean energy. Global energy demand is expected to double by year 2050 and the electricity demands may triple. In this respect, solar energy conversion using photo-voltaic solar cells is an outstanding alternative to fossil fuels, and a large scale industrial sector has emerged, almost exclusively based on silicon-technology. However, the performance of silicon solar cells is fundamentally limited by their conversion efficiency. Hence, disruptive innovations are required for further (and true) penetration of CO2 free energy production, but also for storage, conversion and distribution. The goal of this project is to increase the efficiency of photo-voltaic solar cells and reduce their cost by using abundant and environmental-friendly materials. This will be achieved by tailoring the properties of zinc-oxide (ZnO) and gallium-oxide (Ga2O3) by introducing semiconducting nanoparticles. The oxide matrix will then act both as an extra absorber of sunlight, and as a conductor of current produced by the cell. This will then be integrated as a transparent conductor into a larger device compatible with the existing silicon based technology, thereby increasing the total efficiency. We have studied the formation of germanium and iron rich semiconducting particles in zinc oxide and how these particles absorb light in the visible range of the spectrum. The iron rich particles have proven particularly interesting for absorption at the relevant energies. We have therefore further investigated the formation of such particles in thin films of zinc oxide, a crucial step towards incorporation in devices together with existing Si-cell technology. In early 2023 we will start constructing a demonstrator to test the total efficiency of this system. This part of the project has so far resulted in 7 conference contributions, three master’s theses, and two scientific articles. Furthermore, we have investigated the modification of gallium oxide by means of ion implantation, whereby highly energetic ions of Si, Ge, Au, and Ni are introduced into single crystals of gallium oxide. Through this process and subsequent heat treatment we are able to control the composition, crystal structure, and creation of nanoparticles and thereby control how the material absorbs light. Here the result have been published in three conference contributions and two scientific articles. Finally, we have worked with metallic nanoparticles and studied how they absorb light through the excitation of localized surface plasmon resonance. This is an alternative to absorbing light through the semiconducting particles described above, where the wavelength absorbed can be controlled by varying the composition, shape, and size of the particles. This has so far resulted in two conference contributions and one scientific article.

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A paramount challenge facing our common global future is access to sufficient supply of clean energy. Global energy demand is expected to double by year 2050 and the electricity demands will even triple. In this respect, solar energy conversion using PV is an outstanding alternative and a large scale industrial sector has emerged, almost exclusively based on silicon-technology. However, the performance of Si solar cells is fundamentally limited by their conversion efficiency. Hence, disruptive innovations are required for further (and true) penetration of fossil-free energy production, but also for storage, conversion and distribution. Different concepts have been suggested to overcome the Shockley-Queisser limit for conversion efficiency, such as implementation of high cost tandem cells, introduction of impurity band and intermediate band devices, hot electron extraction, and carrier multiplication (CM). An intriguing approach is to join one or more of these new concepts with the prevailing silicon technology. For instance, there is today a trend towards replacing the isolating Si-nitride-based anti-reflective (AR) coating with a transparent conductive oxide (TCO) layer; as a result, charge collection is enhanced and shadowing effects caused by the contact metal fingers are reduced. Moreover, this also opens up a multitude of possibilities to add new functionalities utilizing oxide semiconductors. The objectives of FUNCTION target increased efficiency of PV (solar cells), reducing costs, and improving energy efficiency through the use of abundant (environmental-friendly) materials. This will be achieved by tailoring the properties of a ZnO TCO through the introduction of semiconducting nanoparticles, and integrating it into a larger heterostructure device compatible with the existing Si-based technology.