Invisibility cloak focuses on enhancing solar cell efficiency
Solar panels modules that are presently mounted on roofs convert one fifth of the light into electricity, which means that about 80% of the solar energy are lost.
Up to one tenth of the surface area of solar cells is covered by so-called contact fingers that extract the current generated. At the locations of these contact fingers, light cannot reach the active area of the solar cell and efficiency of the cell decreases.
“Our model experiments have shown that the cloak layer makes the contact fingers nearly completely invisible,” explained doctoral student Martin Schumann of the KIT Institute of Applied Physics, who conducted the experiments and simulations. Physicists of KIT around project head Carsten Rockstuhl, together with partners from Aachen, Freiburg, Halle, Jena, and Jülich, modified the optical invisibility cloak designed at KIT for guiding the incident light around the contact fingers of the solar cell.
Normally, invisibility cloak research is aimed at making objects invisible. For this purpose, light is guided around the object to be hidden. The research project did
not focus on hiding the contact fingers visually, but on the deflected light that reaches the active surface area of the solar cell thanks to the invisibility cloak
and, hence, can be used.
To achieve the cloaking effect, the scientists pursued two approaches. Both are based on applying a polymer coating onto the solar cell. The coating has to possess exactly calculated optical properties, i.e. an index of refraction that depends on the location or a special surface shape. The second concept is promising, as it can potentially be integrated into mass production of solar cells at low costs. The surface of the cloak layer is grooved along the contact fingers. In this way, incident light is refracted away from the contact fingers and finally reaches the active surface area of the solar cell.
By means of a model experiment and detailed simulations, the researchers demonstrated that both concepts are suited for hiding the contact fingers. In the next step, it is planned to apply the cloaking layer onto a solar cell in order to determine the efficiency increase. The physicists are optimistic that efficiency will be improved by the cloak under real conditions: “When applying such a coating onto a real solar cell, optical losses via the contact fingers are supposed to be reduced and efficiency is assumed to be increased by up to 10%,” said Martin Schumann.
Reference
Martin F. Schumann, Samuel Wiesendanger, Jan Christoph Goldschmidt, Benedikt Bläsi, Karsten Bittkau, Ulrich W. Paetzold, Alexander Sprafke, Ralf B. Wehrspohn, Carsten Rockstuhl, and Martin Wegener, ‘Cloaked contact grids on solar cells by coordinate transformations: designs and prototypes’, Optica 2, 850-853 (2015).
DOI: 10.1364/OPTICA.2.000850
Related articles and links:
www.kit.edu/kit/english/pi_2015_110_invisibility-cloak-might-enhance-efficiency-of-solar-cells.php
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