NEMA October 2009 ElectroIndustry - 15

electroindustry news › Opportunities for Standards for Nanotech Applications in Solar Energy Light Up Loucas Tsakalakos, PhD, General Electric Global Research Center Solar energy applications continue to be of immense technological and market interest because of their potential for clean, renewable energy. The solar photovoltaic (PV) market in particular has grown at a tremendous rate over the last decade, and though certainly the recent recession has cooled that off, strong growth rates are expected in the coming future. Currently, PV technology makes up only a small fraction of energy production worldwide. This is due to the relatively higher costs associated with PV methods, and for some technologies, lower efficiencies. In some locations, however, the cost of energy (in $/kWh) produced by conventional fossil fuelbased methods has risen and hence “grid parity” is close to being achieved. In most markets, however, many experts project grid parity will be reached within the next decade. Regardless, there is a strong impetus to reduce the cost of PV modules and systems while simultaneously increasing the power conversion efficiency. THE HIGH EFFICIENCY PV CONCEPT While today’s technology is capable of meeting the demands of many markets, there has been strong interest within the research and development community to develop novel energy conversion and PV device concepts for photovoltaics based on nanotechnology. Examples of new nano-enabled energy conversion mechanisms include multiplebandgap junctions, intermediate bands, multi-exciton generation, hot electron solar cells, down conversions, up conversion, and thermophotonics1. Many of these concepts may use nanotechnology for practical implementation. Out of all of these concepts, only the multiple-bandgap junction mechanism is available commercially in a III-V thin fi lm device format 2. Indeed, all classes of nanostructures have been applied to these novel concepts3. Bulk nanocomposites are being applied in dye-sensitized solar cells, also known as Grätzel cells, polymer/organic solar cells, and in inorganic nanocomposite devices. Two-dimensional nanostructures such as quantum wells have been demonstrated in high efficiency gallium arsenide-based devices. One-dimensional nanowire solar cells are currently being explored in a variety of materials systems including silicon, amorphous silicon, and CdTe (see figure). Finally, zero-dimensional nanoparticles and quantum dots are being applied in several different functionalities, including quantum dot devices, up/down conversion, and plasmonics based on metal nanoparticles. TOPICS FOR STANDARDS While some of these concepts may be relatively far away from commercialization, the further development and future introduction of such high efficiency PV modules will create new needs for standardization. At the R&D level, standard tests for measuring the structural, optical, and optoelectronic properties of relevant nanostructures should be considered. There may also be an interest in standard test procedures for measuring the performance of PV cells based on nanostructures at different size scales, since area uniformity must be considered. In the longer term, the introduction of high efficiency devices to the terrestrial market may have an impact on the balance of systems (BOS) required to efficiently convert dc electricity to ac, as well as to store energy. Components such as junction boxes, bypass diodes, and inverters should meet standards for performance and reliability. Energy storage will also be increasingly important for high efficiency system applications, hence standards for batteries and/or ultracapacitors in high efficiency PV systems should also be considered. In summary, the application of nanotechnology to solar energy applications by multiple means is a topic of strong interest in the R&D community, with many exciting developments frequently reported. While from a commercial perspective, most of these applications are in the early stage, opportunities for creating standards for development and PV BOS components may arise in the coming years as these technologies mature. ei Cross-sectional scanning electron microscope image of silicon nanowires being explored for advanced solar cells. References 1. M.A. Green, Third Generation Photovoltaics: Advanced Solar Energy Conversion (Springer-Verlag, Berlin, 2003) 2. H. Yoon, J.E. Granata, P. Hebert, R.R. King, C.M. Fetzer, P.C. Colter, K.M. Edmondson, D. Law, G.S. Kinsey, D.D. Krut, J.H. Ermer, M.S. Gillanders, and N.H. Karam, Recent Advances in Highefficiency III–V Multi-junction Solar Cells for Space Applications: Ultra Triple Junction Qualification, Prog. Photovolt: Res. Appl.13 (2005) 133 3. L. Tsakalakos, “Nanostructures for Photovoltaics,” Mater. Sci. Eng. R 62, 175-189 (2008); L. Tsakalakos, Ed. Nanotechnology for Photovoltaics (Taylor & Francis Press, Boca Raton, 2010), in press NEMA electroindustry • October 09

NEMA October 2009 ElectroIndustry

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