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FEATURE INTRODUCTION Savings potential of interior lighting


Solid-


state lighting is now a mature technology that is rapidly climbing in share among the different


commercial lighting technologies





FOR MORE INFORMATION VISIT


Market data www.eupd-research.com www.ihs.com www.yole.fr


Research and Technology www.irec.cat (Spain) www.ise.fraunhofer.de (Germany) www.tno.nl (The Netherlands)


Carlos Lee, Director General EPIC – European Photonics Industry Consortium, 14 Rue de la Science, 1040 Brussels, Belgium carlos.lee@epic-assoc.com www.epic-assoc.com/members


6 PHOTONICS FOR RENEWABLE ENERGY 2013


cover coatings, nanostructured transparent conductors, up- or down-converters, and plasmonic scatterers. Integration of such nanotechnology requires optimisation of the complete device on levels ranging from atomistic, molecular to continuum involving optics, electronics and thermal phenomena. The more light that is put into a solar cell, the higher the output will be in principle. There are several aspects of optics and photonics that can contribute to photovoltaics. Light management technology, for instance, can improve the incoupling of light. A first example of this is the use of an antireflection coating based on nanostructured surfaces or materials. In contrast to MgF2


-


based antireflection coatings, this type of solution works over a much wider wavelength range. This is important because solar cells use typically light between 350 nm and 1100 nm, a broader range than in most other


optoelectronic applications. Moreover, nanostructured surfaces can have low a reflection regardless of the incident angle, while chemically stable materials such as silica can be used. These factors make them suitable specifically for solar cells.


A question of size


Another function of advanced optics and nanophotonics can be found in high-efficiency thin film solar cells. Solar cell materials are often quite expensive and a major cost reduction can be achieved by using less material – for instance, by making absorber layers thinner. The drawback is that, as the solar cell material gets thinner, less light is absorbed. Nanotexturing and structured back reflectors can help to compensate these optical losses. At TNO, where the thickness of the absorber layer in CIGS solar cells has been reduced from two microns to less than 0.5 microns, light management technology is being implemented. Moreover, nanophotonics can also be


applied in solar cells, because plasmonic materials can enhance the ability of a solar cell to absorb the light.


Another challenge is the


interconnection of solar cells. Wafer-based solar cells are usually interconnected by soldering, whereas upcoming thin film technology relies on another photonics technology, i.e. laser scribing, and deposition of transparent conductors. ‘TNO has combined thin metallic lines on commercially available transparent conductors to improve the conductivity by two orders of magnitude, at the cost of only a few per cent in optical losses,’ says Joop van Deelen, senior scientist at TNO. Their modelling has indicated that solar panels with an initial energy conversion efficiency of 11.7 per cent can be upgraded to 13.8 per cent when using this technology.


How does this affect the supply chain? Laser manufacturer Rofin recently saw a rising demand for laser systems to


(Source: CELMA 2011)


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