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Coloured SIS Solar Cells for Enhanced Building Designs

Kevin Füchsel knows why solar researchers have not collaborated more with architects and designers in the past to allow solar technology to enhance the design of a structure, as opposed to compromising a buildings or home‘s curb appeal. They were too busy making cells more efficient and reducing production costs. The look and feel of solar products and customised design was not on the agenda in this highly price-driven business, says the project manager at the Fraunhofer Institute for Applied Optics and Precision Engineering IOF in Jena, Germany. The field of building integrated photovoltaics is still a niche market with a market share of round about 1% hence it was not interesting for the competitors.

The dark solar panels presently available on the market could hardly be termed customised photovoltaics. A group of optics specialists from Fraunhofer as well as from the Friedrich-Schiller University, also in Jena, are working to change that by exploring cost-effective techniques and manufacturing processes to increase both the efficiency of solar panels and the design flexibility they give architects and designers. Füchsel and his collaborators realise this research is giving them the opportunity to create new kinds of solar modules with an aesthetically appealing design and a great variety of colours.

Solar Novus Today had recently reported on related efforts out of Switzerland Coloured Glass for Solar Panels.

As part of their publically funded research work on efficient cell concepts over the past few year, Füchsel and his team at one point posed the question, How can we use the capabilities of these technologies to make products that are efficient and have a unique design as well. Thus, the efficient design idea was born (more info at www.efficientdesign.de).

Made from paper-thin crystalline silicon wafers, the simply constructed SIS (semiconductor-insulator-semiconductor) solar cell has an optically neutral protective barrier (insulator), onto which a hundred-nanometre-thick transparent conductive oxide (TCO) layer is applied to guide as many light particles as possible to the semiconductor layer below. What is more, since TCO has a lower refractive index than silicon it also functions as an anti-reflective coating.

Different colours of the solar panels are achieved by either varying the thickness of the TCO layer or modifying its refractive index. It is possible to use the cells in conjunction with other wafer-based silicon technologies. Hence, efficient design modules can be combined with standard modules from other suppliers.

According to Füchsel, giving solar cells colour does not actually affect their efficiency. The additional transparent TCO layer has barely any impact on the current yield. Simulations showed that SIS cells could be up to 20% efficient, which is pretty close to the efficiency range we want to be in, Füchsel says. In practice, on the other hand, the efficiency would depend on the design of the solar panels and the direction the building faces.

Laser-based optical welding processes will allow scientists to connect several solar cells to create a single module and accurate work at a micrometer scale without damaging the surrounding material. Researchers are also developing an inkjet printing process to deposit the conductive TCO layer on the silicon wafer. This will make manufacturing faster and allow additional degrees of flexibility in design. SIS solar cells could even be used to make large billboards that produce their own electricity such as for a building to communicate information, displaying the name of a company or even artistic pictures. If architects, designers, building owners and photovoltaic specialists collaborate closely, Füchsel expects more pleasing and colourful building designs. Hopefully, our PV technologies will colour up the cities of the future, he says in conclusion.

Written by Sandra Henderson, Research Editor, Solar Novus Today

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