Transparent solar cells power smart sunglasses

Technology News |
By Nick Flaherty

“We bring the energy where there is no other solar technology,” says Dr. Alexander Colsmann, Head of the Organic Photovoltaics Working Group at the Lichttechnisches Institut (LTI) of KIT. The “smart” sunglasses produced by the scientist and his team at the Karlsruhe Institute of Technology (KIT) as a product study supply themselves with electricity for integrated electronic devices – in this case, a circuit that measures and displays sun radiation intensity and ambient temperature. The solar cell coated lenses, which are fitted into a commercially available plastic frame, are each 1.6 millimeters thick and weigh about six grams – similar to the glasses of conventional sunglasses. The microprocessors and the two displays are integrated in the brackets, on which the information on the sun’s strength and ambient temperature can be read in a bar graph. The solar glasses also function in the interior with a minimum lighting intensity of 500 lux, which corresponds to the usual office or living room lighting. Each of the two “smart” spectacle lenses under ambient lighting produces 200 microwatts of electrical power which would be sufficient to allow applications such as a hearing aid or a step counter.

“This is an example of the many conceivable mobile applications of organic solar cells, which classical photovoltaics do not allow,” emphasizes PhD student Dominik Landerer, who has contributed significantly to the development of solar glasses at the KIT’s Material Science Center for Energy Systems. Their mechanical flexibility and the possibility to adapt them in color, transparency, shape and size to the respective application, make the solar cells based on hydrocarbon compounds from the engineer’s point of view an interesting material.

Another potential application area for the organic solar cells is integration in buildings: since glass façades, such as those of high-rise buildings, often have to be darkened, it is obvious to use the absorbed light for the generation of electricity by means of organic solar modules, according to Colsmann. A vision is to coat large areas in a cost-effective way with organic solar cells in a roll-to-roll process, says the engineer, who works on the basic physics and chemistrry of organic solar cells and semiconductor components at KIT’s Materials Science Center for Energy Systems.

The research was supported by the German Federal Ministry of Education and Research (BMBF), in the context of the project POPUP for the development of new materials and device structures for competitive mass production processes and applications of organic photovoltaics.

The study of solar sunglasses has first been published by the KIT scientists in the magazine Energy Technology, entitled “Solar Glasses: A Case Study on Semitransparent Organic Solar Cells for Self-Powered, Smart Wearable Devices”.

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