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Johannes Gutmann, born 04/04/1985 in Freiburg, Germany,
graduated 2009 in Microsystems Engineering at University of Freiburg. He concentrated on system design, i.e. microelectronics, design of microsystems, simulation and optics. His thesis with the title "Extraction of Nonlinear Piezoresistance Coefficients of Crystalline Silicon" on so far unknown material properties of silicon was supervised by Prof. O. Paul. In parallel, Johannes studied economics. He took part in scientific and also in business competitions like management simulations. He worked as student assistant at the Department of Microsystems Engineering, Freiburg and at Bosch Sensortec, Reutlingen and he was research intern with the Robert Bosch Research and Technology Center in Palo Alto, CA, USA.
"Theoretical and Experimental Analysis of Photon Management Systems with Luminescent Materials and Photonic Structures":
In order to spread solar energy generation cutting costs as well as expanding the application range is necessary. Concentrating the sunlight before it hits the solar cell reduces the needed cell area and thus can lower the costs. This approach is realized in so called fluorescent concentrators. In contrast to mirror and lens based system they are capable of concentrating not only direct but also diffuse radiation enabling their use in regions like Germany. Further, new design possibilities offer various application options such as building integrated photovoltaics.
Conventional fluorescent concentrators consist of transparent glass or plastic sheets (as they are used in classic photovoltaic modules) which are doped with fluorescent materials such as organic dyes. Thus incoming radiation is absorbed by these materials inside the sheet and emitted again as light with longer wavelength. Most of the emitted light is trapped by total internal reflection inside the sheet and it is guided to the edges. With a collector area larger than the area of the edge faces, a concentration of the light can be achieved. Solar cells put on these edge faces can convert the light into electrical energy. However, this way of concentrating light is not lossless: Only 26% of the emitted light can be captured by total internal reflection. Another loss mechanism is reabsorption. State of the art systems achieve efficiencies of up to 7%. For commercial use, however, the system efficiency needs to be increased.
The new concept called "NanoFluko" investigated in this PhD project aims to minimize the losses of conventional fluorescent concentrators. The fluorescent molecules shall be embedded in photonic structures to optimize light guiding. This further modifies the emission characteristics to enhance emission towards the edges as well as mitigate the effect of reabsorption. Reducing in particular path length dependant loss can help fabricating larger and more efficient fluorescent concentrators. In this work the relevant structures and processes shall be investigated theoretically and simulated. Furthermore, the "NanoFluko" shall be fabricated and extensively characterized.