{"72223":{"#nid":"72223","#data":{"type":"news","title":"3D Solar Cells Boost Efficiency, Reduce Size","body":[{"value":"\u003Cp\u003EUnique three-dimensional solar cells that capture nearly all of the light that strikes them could boost the efficiency of photovoltaic (PV) systems while reducing their size, weight and mechanical complexity.  \u003C\/p\u003E\n\u003Cp\u003EThe new 3D solar cells capture photons from sunlight using an array of miniature \u0027tower\u0027 structures that resemble high-rise buildings in a city street grid.  The cells could find near-term applications for powering spacecraft, and by enabling efficiency improvements in photovoltaic coating materials, could also change the way solar cells are designed for a broad range of applications.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022Our goal is to harvest every last photon that is available to our cells,\u0022 said Jud Ready, a senior research engineer in the Electro-Optical Systems Laboratory at the Georgia Tech Research Institute (GTRI).  \u0022By capturing more of the light in our 3D structures, we can use much smaller photovoltaic arrays.  On a satellite or other spacecraft, that would mean less weight and less space taken up with the PV system.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EThe 3D design was described in the March 2007 issue of the journal \u003Cem\u003EJOM\u003C\/em\u003E, published by The Minerals, Metals and Materials Society.  The research has been sponsored by the Air Force Office of Scientific Research, the Air Force Research Laboratory, NewCyte Inc., and Intellectual Property Partners, LLC.  A global patent application has been filed for the technology.\n\u003C\/p\u003E\n\u003Cp\u003EThe GTRI photovoltaic cells trap light between their tower structures, which are about 100 microns tall, 40 microns by 40 microns square, 10 microns apart -- and built from arrays containing millions of vertically-aligned carbon nanotubes.  Conventional flat solar cells reflect a significant portion of the light that strikes them, reducing the amount of energy they absorb.\n\u003C\/p\u003E\n\u003Cp\u003EBecause the tower structures can trap and absorb light received from many different angles, the new cells remain efficient even when the sun is not directly overhead.  That could allow them to be used on spacecraft without the mechanical aiming systems that maintain a constant orientation to the sun, reducing weight and complexity - and improving reliability.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022The efficiency of our cells increases as the sunlight goes away from perpendicular, so we may not need mechanical arrays to rotate our cells,\u0022 Ready noted.\n\u003C\/p\u003E\n\u003Cp\u003EThe ability of the 3D cells to absorb virtually all of the light that strikes them could also enable improvements in the efficiency with which the cells convert the photons they absorb into electrical current.  \n\u003C\/p\u003E\n\u003Cp\u003EIn conventional flat solar cells, the photovoltaic coatings must be thick enough to capture the photons, whose energy then liberates electrons from the photovoltaic materials to create electrical current.  However, each mobile electron leaves behind a \u0022hole\u0022 in the atomic matrix of the coating.  The longer it takes electrons to exit the PV material, the more likely it is that they will recombine with a hole -- reducing the electrical current.\n\u003C\/p\u003E\n\u003Cp\u003EBecause the 3D cells absorb more of the photons than conventional cells, their coatings can be made thinner, allowing the electrons to exit more quickly, reducing the likelihood that recombination will take place.  That boosts the \u0022quantum efficiency\u0022 - the rate at which absorbed photons are converted to electrons - of the 3D cells.\n\u003C\/p\u003E\n\u003Cp\u003EFabrication of the cells begins with a silicon wafer, which can also serve as the solar cell\u0027s bottom junction.  The researchers first coat the wafer with a thin layer of iron using a photolithography process that can create a wide variety of patterns.  The patterned wafer is then placed into a furnace heated to 780 degrees Celsius.  Hydrocarbon gases are then flowed into furnace, where the carbon and hydrogen separate.  In a process known as chemical vapor deposition, the carbon grows arrays of multi-walled carbon nanotubes atop the iron patterns.\n\u003C\/p\u003E\n\u003Cp\u003EOnce the carbon nanotube towers have been grown, the researchers use a process known as molecular beam epitaxy to coat them with cadmium telluride (CdTe) and cadmium sulfide (CdS) which serve as the p-type and n-type photovoltaic layers.  Atop that, a thin coating of indium tin oxide, a clear conducting material, is added to serve as the cell\u0027s top electrode.\n\u003C\/p\u003E\n\u003Cp\u003EIn the finished cells, the carbon nanotube arrays serve both as support for the 3D arrays and as a conductor connecting the photovoltaic materials to the silicon wafer.\n\u003C\/p\u003E\n\u003Cp\u003EThe researchers chose to make their prototypes cells from the cadmium materials because they were familiar with them from other research.  However, a broad range of other photovoltaic materials could also be used, and selecting the best material for specific applications will be a goal of future research.  \n\u003C\/p\u003E\n\u003Cp\u003EReady also wants to study the optimal heights and spacing for the towers, and to determine the trade-offs between spacing and the angle at which the light hits the structures.\n\u003C\/p\u003E\n\u003Cp\u003EThe new cells face several hurdles before they can be commercially produced.  Testing must verify their ability to survive launch and operation in space, for instance.  And production techniques will have to scaled up from the current two-inch laboratory prototypes.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022We have demonstrated that we can extract electrons using this approach,\u0022 Ready said.  \u0022Now we need to get a good baseline to see where we compare to existing materials, how to optimize this and what\u0027s needed to advance this technology.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EIntellectual Property Partners of Atlanta holds the rights to the 3D solar cell design and is seeking partners to commercialize the technology.\n\u003C\/p\u003E\n\u003Cp\u003EAnother commercialization path is being followed by an Ohio company, NewCyte, which is partnering with GTRI to use the 3D approach for terrestrial solar cells.  The Air Force Office of Scientific Research has awarded the company a Small Business Technology Transfer (STTR) grant to develop the technology.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022NewCyte has patent pending, low cost technology for depositing semiconductor layers directly on individual fullerenes,\u0022 explained Dennis J. Flood, NewCyte\u0027s president and CTO.  \u0022We are using our technology to grow the same semiconductor layers on the carbon nanotube towers that GTRI has already demonstrated.  Our goal is to achieve performance and cost levels that will make solar cells using the GTRI 3D cell structure competitive in the broader terrestrial solar cell market.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EIn addition to Ready, other Georgia Tech researchers contributing to the work include R.E. Camacho, A.R. Morgan, M.C. Flores, T.A. McLeod, V.S. Kumsomboone, B.J. Mordecai, R. Bhattacharagjea, W. Tong, B.K. Wagner, J.D. Flicker and S.P. Turano.\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EResearch News \u0026amp; Publications Office\u003Cbr \/\u003E\nGeorgia Institute of Technology\u003Cbr \/\u003E\n75 Fifth Street, N.W., Suite 100\u003Cbr \/\u003E\nAtlanta, Georgia  30308  USA\u003C\/strong\u003E\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EMedia Relations Contacts\u003C\/strong\u003E: John Toon (404-894-6986); E-mail: (\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E) or Kirk Englehardt (404-407-7280); E-mail: (\u003Ca href=\u0022mailto:kirk.englehardt@gtri.gatech.edu\u0022\u003Ekirk.englehardt@gtri.gatech.edu\u003C\/a\u003E).\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003ETechnical Contact\u003C\/strong\u003E: Jud Ready (404-407-6036); E-mail: (\u003Ca href=\u0022mailto:jud.ready@gtri.gatech.edu\u0022\u003Ejud.ready@gtri.gatech.edu\u003C\/a\u003E).\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EWriter\u003C\/strong\u003E: John Toon\n\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":[{"value":"New design uses \u0027nano-Manhattan\u0027 carbon nanotube towers"}],"field_summary":[{"value":"Unique three-dimensional solar cells that capture nearly all of the light that strikes them could boost the efficiency of photovoltaic (PV) systems while reducing their size, weight and mechanical complexity.","format":"limited_html"}],"field_summary_sentence":[{"value":"Design captures more light with nanotube towers"}],"uid":"27303","created_gmt":"2007-04-11 00:00:00","changed_gmt":"2016-10-08 03:03:29","author":"John Toon","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2007-04-11T00:00:00-04:00","iso_date":"2007-04-11T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"72224":{"id":"72224","type":"image","title":"Holding solar cell","body":null,"created":"1449177446","gmt_created":"2015-12-03 21:17:26","changed":"1475894653","gmt_changed":"2016-10-08 02:44:13"},"72225":{"id":"72225","type":"image","title":"Cross-section of nanotowers","body":null,"created":"1449177446","gmt_created":"2015-12-03 21:17:26","changed":"1475894653","gmt_changed":"2016-10-08 02:44:13"},"72226":{"id":"72226","type":"image","title":"Displaying solar cell","body":null,"created":"1449177446","gmt_created":"2015-12-03 21:17:26","changed":"1475894653","gmt_changed":"2016-10-08 02:44:13"}},"media_ids":["72224","72225","72226"],"related_links":[{"url":"http:\/\/www.gtri.gatech.edu\/","title":"Georgia Tech Research Institute"},{"url":"http:\/\/www-stage.gatech.edu\/news-room\/flash\/CNTpv.html","title":"Animation of solar cell operation"}],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[{"id":"144","name":"Energy"},{"id":"145","name":"Engineering"},{"id":"154","name":"Environment"},{"id":"135","name":"Research"}],"keywords":[{"id":"213","name":"energy"},{"id":"7292","name":"light"},{"id":"7566","name":"photons"},{"id":"1073","name":"photovoltaic"},{"id":"170889","name":"solar-cell"}],"core_research_areas":[],"news_room_topics":[],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cstrong\u003EJohn Toon\u003C\/strong\u003E\u003Cbr \/\u003EResearch News \u0026amp; Publications Office\u003Cbr \/\u003E\u003Ca href=\u0022http:\/\/www.gatech.edu\/contact\/index.html?id=jt7\u0022\u003EContact John Toon\u003C\/a\u003E\u003Cbr \/\u003E\u003Cstrong\u003E404-894-6986\u003C\/strong\u003E","format":"limited_html"}],"email":["jtoon@gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}