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December 2015 • SMT Magazine 23 tal agencies, programs, and contractors to share with and learn to better understand industry needs and to assist in conforming to the neces- sary policies. Q: What are smtA's most successful programs and why? A: Our local chapters are very successful as they get to the grass roots of people in the industry. They are hosting events addressing technical issues that speak to their specific region and helping real people solve real problems. SMTA International is our flagship technical confer- ence as it successfully accomplishes our mis- sion of sharing the knowledge on the largest scale. Q: Why should someone join smtA? A: Membership in the SMTA delivers a competi- tive advantage to individuals and companies by allowing them to tap into a network of some of the brightest minds in the industry, enhancing your reputation as someone who is involved and aware of emerging trends and learning in- novative manufacturing practices. You'll be part of a welcoming and inclusive association shar- ing original, high quality, and ground breaking work with people around the world. SmT A solar cell's widely used design has a flaw: the shiny metal on top of the cell actually re- flects sunlight away from the semiconductor where electricity is produced, reducing the cell's efficiency. now, Stanford university scientists have dis- covered how to hide the reflective upper contact and funnel light directly to the semiconductor below. Their findings could lead to a new para- digm in the design and fabrication of solar cells. "using nanotechnology, we have devel- oped a novel way to make the upper metal contact nearly invisible to incom- ing light," said study lead author vijay narasimhan, who conducted the work as a graduate student at Stanford. "our new tech- nique could significantly improve the efficiency and thereby lower the cost of solar cells." in most solar cells, the upper contact consists of a metal wire grid that carries electricity to or from the device. But these wires also prevent sunlight from reaching the semiconductor. "The more metal you have on the surface, the more light you block," said study co-author Yi Cui, an associate professor of materials science and engineering. "That light is then lost and cannot be converted to electricity." Metal contacts, therefore, "face a seemingly irreconcilable tradeoff between electrical con- ductivity and optical transparency," narasimhan added. "But the nanostructure we created elimi- nates that tradeoff." For the study, the Stanford team placed a 16-nanometer-thick film of gold on a flat sheet of silicon. The gold film was riddled with an ar- ray of nanosized square holes, but to the eye, the surface looked like a shiny, gold mirror. optical analysis re- vealed that the perforated gold film covered 65 per- cent of the silicon surface and reflected, on average, 50 percent of the incom- ing light. The scientists reasoned that if they could somehow hide the reflec- tive gold film, more light would reach the silicon semiconductor below. Stanford Technology Makes Metal Wires on Solar Cells Nearly Invisible to Light A cLoSer LooK AT SmTA FeATureD Q&A

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