Solar energy is an important renewable energy and plays a major role in the energy transition. Herein, photovoltaics is a growing field that promises to establish solar energy harvesting both in large-scale power plants as well as in urban spaces and shows a trend of increasing production capacity and speed, and decreasing costs. However, mastering the energy transition within a few decades demands a further boost in production speed. A way to achieve such a boost is concentrated photovoltaics (CPV): by placing a solar cell in the focus of a low-cost solar concentrator, the cells required area size can be reduced by the concentration factor of the solar concentrator. However, CPV needs sun trackers to mechanically adjust the solar concentrator to the sun. Herein, sun trackers have crucial drawbacks such as high costs, large weight, bulkiness, and high precision demands.In this thesis, waveguide systems are investigated with regard to their capability of improving CPV and establishing mechanics-free, thin sun trackers. In a first passive system, plasmonic nanoparticles interacting with surface plasmons are found to increase light-matter interaction and show broadband light absorption, which could be used for solar thermal applications. In another passive waveguide system, the TE node modes of symmetric periodic dielectric waveguides show an increase in light concentration by a factor of 1000. In a third passive system, both dielectric and structured plasmonic waveguides form a hybrid waveguide. For certain geometric symmetries, the diffraction of light out of the hybrid waveguide can be suppressed for one wavelength. In an active waveguide system, it is shown that combining active electro-optic waveguides with a structured passive waveguide enables the local control of the coupling into or out of the waveguide over a broad spectral range. This local control, in comb++
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ination with spatially varying structures, is considered a key step for mechanics-free sun trackers.