Papers by Henning Helmers
Solar Energy Materials and Solar Cells, 2009
This study examines concepts for increasing the efficiency of fluorescent concentrator systems. D... more This study examines concepts for increasing the efficiency of fluorescent concentrator systems. Different system sizes and configurations are investigated in detail by external quantum efficiency measurements, light-beam-induced current maps and by I-V measurements. A photonic structure that serves as a bandstop reflection filter for light emitted from dyes in the fluorescent concentrator increases the system efficiency relatively by 20%. Such photonic structures are especially beneficial for larger systems. The combination of two fluorescent concentrators made with different dyes in one stack increases the system efficiency from 5.1% with only one dye to 6.7% for the stack.
IEEE Transactions on Electron Devices, 2010
Monolithic interconnected modules are large-area high-voltage photovoltaic devices that are reali... more Monolithic interconnected modules are large-area high-voltage photovoltaic devices that are realized through solar cell segments that are series-connected via interconnection trenches during wafer processing. This paper investigates different processing techniques, giving detailed information about each processing sequence. In the first approach, a wet chemical etching procedure and photo-defined polyimide as dielectric film is used, leading to minimal trench width of 86 µm. Furthermore, we examine the applicability of advanced processing techniques. An alternative dry-etching process using reactive ion etching in inductively coupled plasma is investigated. With this technique, smooth and near-vertical sidewalls could be achieved, whereas the undercuts in etching profile, which are inevitable when using wet chemical etching, could be avoided. Moreover, an accurate processing technique for plasma-enhanced chemical vapor deposited SiN x as a dielectric film for electrical isolation is presented. This allowed sufficient isolation to be achieved, as well as enabling precise structuring. With these advanced processing techniques, trench widths of 57 µm were realized, resulting in a reduction of area losses due to interconnection from 9% to below 6%.
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Papers by Henning Helmers