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EETE JANUARY 2013

energy harvesting Silicon-based optical fiber with solar-cell capabilities could be woven into solar fabrics By Julien Happich An internAtionAl teAm of chemists, physicists and engi- meters-long fibers but, in principle, our team’s new method neers, led by John Badding, a professor of chemistry at Penn could be used to create bendable silicon solar-cell fibers of over State University, has demonstrated for the first time, a silicon- 10 meters in length,” Badding said. “Long, fiber-based solar based optical fiber with solar-cell capabilities that is scalable cells give us the potential to do something we couldn’t really do to many meters in length. the research opens before: We can take the silicon fibers and weave the door to the possibility of weaving together them together into a fabric with a wide range of solar-cell silicon wires to create flexible, curved applications such as power generation, bat- or twisted solar fabrics. tery charging, chemical sensing and biomedical The team’s new findings build on earlier work devices.” addressing the challenge of merging optical Woven, fiber-based solar cells would be light- fibers with electronic chips, silicon-based inte- weight, flexible configurations that are portable, grated circuits that serve as the building blocks foldable and even wearable.” This material could for most semiconductor electronic devices such then be connected to electronic devices to power as solar cells, computers and cellphones. rather them and charge their batteries. “the military es- than merge a flat chip with a round optical fiber, pecially is interested in designing wearable power the team found a way to build a new kind of opti- sources for soldiers in the field,” Badding added. cal fiber, with its own integrated electronic com- A cross-sectional image of the team members believe that another ponent, thereby bypassing the need to integrate the new silicon-based optical advantage of flexibility in solar-cell materials is fiber-optics with chips. To do this, they used fiber. Shown are layers, the possibility of collecting light energy at vari- high-pressure chemistry techniques to deposit labeled n+, i and p+, that ous angles. “A typical solar cell has only one flat semiconducting materials directly, layer by layer, surface,” Badding said. “But a flexible, curved have been deposited inside into tiny holes in optical fibers. solar-cell fabric would not be as dependent upon the pore of the fiber: Source - Now, in their new research, the team members where the light is coming from or where the sun is have used the same high-pressure chemistry Penn State University in the horizon and the time of day.” techniques to make a fiber out of crystalline silicon semicon- Pier J. A. Sazio of the University of Southampton in the ductor materials that can function as a solar cell, a photovoltaic United Kingdom and one of the team’s leaders added, “Another device that can generate electrical power by converting solar intriguing property of these silicon-fiber devices is that as they radiation into direct-current electricity. “Our goal is to extend are so compact, they can have a very fast response to visible high-performance electronic and solar-cell function to longer laser light. In fact, we fabricated fiber-based photodetectors lengths and to more flexible forms. We already have made with a bandwidth of over 1.8 GHz.” Energy-harvesting textile integrates micro spherical solar cells By Julien Happich IN cOOperATION WITH the industrial technology Center of as an energy- Fukuiprefecture, Japan, Sphelarpowercorporation has suc- generating mat. cessfully prototyped an energy-harvesting textile where spheri- the photovol- cal solar cells are interweaved. taic modules obtained can be not only flexible, but also expand- This result was delivered from an interdisciplinary col- able just like textile. One of the benefits of the Sphelar cell is laboration between Sphelarpower, which uniquely developed that it can receive sunlight more effectively and more uniformly 3-dimensional light capturing than conventional flat solar cells. Hence the solar cells are less Sphelar cells, and the indus- dependent on the angle of incoming light. each spherical solar trial Technologycenter of Fukui cell designed as a multi-layered bead features two electrodes prefecture which serves as in- on opposite sides. novativer&D hub for local textile this structure enables 3-dimensional light capture and industries. First, 1.2mm Sphelar extends the device’s application range, from horizontal instal- cells are aligned and connected lations to integration into curved surfaces and 3-dimensional as a thread which is then woven solar modules. 12 Electronic Engineering Times Europe January 2013 www.electronics-eetimes.com


EETE JANUARY 2013
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