{"id":6595,"date":"2015-11-06T05:50:53","date_gmt":"2015-11-06T05:50:53","guid":{"rendered":"http:\/\/revoscience.com\/en\/?p=6595"},"modified":"2015-11-06T05:50:53","modified_gmt":"2015-11-06T05:50:53","slug":"harvesting-more-energy-from-photons","status":"publish","type":"post","link":"https:\/\/www.revoscience.com\/en\/harvesting-more-energy-from-photons\/","title":{"rendered":"Harvesting more energy from photons"},"content":{"rendered":"

Quantum process increases the number of electrons produced when light strikes a metal-dielectric interface.<\/strong><\/em><\/span><\/p>\n

\"Illustration:<\/a>
Illustration: Christine Daniloff\/MIT<\/figcaption><\/figure>\n

CAMBRIDGE, Mass<\/strong>–Researchers at MIT and elsewhere have found a way to significantly boost the energy that can be harnessed from sunlight, a finding that could lead to better solar cells or light detectors.\u00a0<\/span><\/p>\n

The new approach is based on the discovery that unexpected quantum effects increase the number of charge carriers, known as electrons and \u201choles,\u201d that are knocked loose when photons of light of different wavelengths strikes a metal surface coated with a special class of oxide materials known as high-index dielectrics. The photons generate what are known as surface plasmons \u2014 a cloud of oscillating electrons that has the same frequency as the absorbed photons<\/span><\/p>\n

The surprising finding is reported in the journal\u00a0Physical Review Letters<\/i>\u00a0by authors including MIT\u2019s Nicholas Fang, an associate professor of mechanical engineering, and postdoc Dafei Jin. The researchers used a sheet of silver coated with an oxide, which converts light energy into polarization of atoms at the interface.<\/span><\/p>\n

[pullquote]The surprising finding is reported in the journal\u00a0<\/span>Physical Review Letters<\/i>\u00a0by authors including MIT\u2019s Nicholas Fang, an associate professor of mechanical engineering, and postdoc Dafei Jin.<\/span>[\/pullquote]<\/p>\n

\u201cOur study reveals a surprising fact: Absorption of visible light is directly controlled by how deeply the electrons spill over the interface between the metal and the dielectric,\u201d Fang says. The strength of the effect, he adds, depends directly on the dielectric constant of the material \u2014 a measure of how well it blocks the passage of electrical current and converts that energy into polarization.<\/span><\/p>\n

\u201cIn earlier studies,\u201d Fang says, \u201cthis was something that was overlooked.\u201d\u00a0<\/span><\/p>\n

Previous experiments showing elevated production of electrons in such materials had been chalked up to defects in the materials. But Fang says those explanations \u201cwere not enough to explain why we observed such broadband absorption over such a thin layer\u201d of material. But, he says, the team\u2019s experiments back the newfound quantum-based effects as an explanation for the strong interaction.<\/span><\/p>\n

The team found that by varying the composition and thickness of the layer of dielectric materials (such as aluminum oxide, hafnium oxide, and titanium oxide) deposited on the metal surface, they could control how much energy was passed from incoming photons into generating pairs of electrons and holes in the metal \u2014 a measure of the system\u2019s efficiency in capturing light\u2019s energy. In addition, the system allowed a wide range of wavelengths, or colors, of light to be absorbed, they say.<\/span><\/p>\n

The phenomenon should be relatively easy to harness for useful devices, Fang says, because the materials involved are already widely used at industrial scale. \u201cThe oxide materials are exactly the kind people use for making better transistors,\u201d he says; these might now be harnessed to produce better solar cells and superfast photodetectors.<\/span><\/p>\n

\u201cThe addition of a dielectric layer is surprisingly effective\u201d at improving the efficiency of light harnessing, Fang says. And because solar cells based on this principle would be very thin, he adds, they would use less material than conventional silicon cells.<\/span><\/p>\n

Because of their broadband responsiveness, Fang says, such systems also respond much faster to incoming light: \u201cWe could receive or detect signals as a shorter pulse\u201d than current photodetectors can pick up, he explains. This could even lead to new \u201cli-fi\u201d systems, he suggests \u2014 using light to send and receive high-speed data.<\/span><\/p>\n

The team also included postdoc Qing Hu and graduate student Yingyi Yang at MIT, Daniel Neuhauser at the University of California at Los Angeles, Felix von Cube and David Bell at Harvard University, Ritesh Sachan at Oak Ridge National Laboratory, and Ting Luk at Sandia National Laboratories. The work was supported by the National Science Foundation and the Air Force Office of Scientific Research.<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

Researchers at MIT and elsewhere have found a way to significantly boost the energy that can be harnessed from sunlight, a finding that could lead to better solar cells or light detectors. <\/p>\n","protected":false},"author":6,"featured_media":6596,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[17],"tags":[],"class_list":["post-6595","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-research"],"featured_image_urls":{"full":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/11\/MIT-Absorbing-photons-1_0.jpg",639,426,false],"thumbnail":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/11\/MIT-Absorbing-photons-1_0-150x150.jpg",150,150,true],"medium":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/11\/MIT-Absorbing-photons-1_0-300x200.jpg",300,200,true],"medium_large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/11\/MIT-Absorbing-photons-1_0.jpg",639,426,false],"large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/11\/MIT-Absorbing-photons-1_0.jpg",639,426,false],"1536x1536":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/11\/MIT-Absorbing-photons-1_0.jpg",639,426,false],"2048x2048":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/11\/MIT-Absorbing-photons-1_0.jpg",639,426,false],"ultp_layout_landscape_large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/11\/MIT-Absorbing-photons-1_0.jpg",639,426,false],"ultp_layout_landscape":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/11\/MIT-Absorbing-photons-1_0.jpg",639,426,false],"ultp_layout_portrait":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/11\/MIT-Absorbing-photons-1_0.jpg",600,400,false],"ultp_layout_square":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/11\/MIT-Absorbing-photons-1_0.jpg",600,400,false],"newspaper-x-single-post":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/11\/MIT-Absorbing-photons-1_0.jpg",639,426,false],"newspaper-x-recent-post-big":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/11\/MIT-Absorbing-photons-1_0.jpg",540,360,false],"newspaper-x-recent-post-list-image":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/11\/MIT-Absorbing-photons-1_0.jpg",95,63,false],"web-stories-poster-portrait":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/11\/MIT-Absorbing-photons-1_0.jpg",639,426,false],"web-stories-publisher-logo":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/11\/MIT-Absorbing-photons-1_0.jpg",96,64,false],"web-stories-thumbnail":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2015\/11\/MIT-Absorbing-photons-1_0.jpg",150,100,false]},"author_info":{"info":["Amrita Tuladhar"]},"category_info":"Research<\/a>","tag_info":"Research","comment_count":"0","_links":{"self":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/6595","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/users\/6"}],"replies":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/comments?post=6595"}],"version-history":[{"count":0,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/6595\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/media\/6596"}],"wp:attachment":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/media?parent=6595"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/categories?post=6595"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/tags?post=6595"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}