{"71133":{"#nid":"71133","#data":{"type":"news","title":"Research Reveals Factors That Affect Organic-based Device Efficiency","body":[{"value":"\u003Cp\u003EOrganic-based devices, such as organic light-emitting diodes, require a transparent conductive layer with a high work function, meaning it promotes injection of electron holes into an organic layer to produce more light. \u003C\/p\u003E\n\u003Cp\u003EResearch presented on July 8 at the International Conference on Science and Technology of Synthetic Metals in Brazil provides insight into factors that influence the injection efficiency. A balanced injection of positive and negative charge carriers into the organic layer is important to achieve high quantum efficiency, but the interface between the metallic coating and organic layer where the injection occurs is poorly understood.\n\u003C\/p\u003E\n\u003Cp\u003EPlacing an organic layer on top of the conductive layer modifies each layer\u0027s individual work function, or the minimum energy needed to extract the first electron from the metal. \n\u003C\/p\u003E\n\u003Cp\u003E\u0022Measuring the work functions independently for each layer does not provide an indication of how their energy levels match when they touch each other,\u0027 explained Jean-Luc Br\u00c3\u00a9das, a computational materials chemist, professor in the Georgia Institute of Technology\u0027s School of Chemistry and Biochemistry and Georgia Research Alliance Eminent Scholar. \n\u003C\/p\u003E\n\u003Cp\u003EThe energy levels for each layer should align when attached; otherwise, a barrier will form and a higher voltage will be required to send current in. \n\u003C\/p\u003E\n\u003Cp\u003EWith funding from the Office of Naval Research, Br\u00c3\u00a9das first developed a theoretical model of the interface between conventional metals and a single layer of organic molecules forming a self-assembled monolayer on the metal. His goal was to determine how the metal work function could be modified by depositing the self-assembled monolayer.\n\u003C\/p\u003E\n\u003Cp\u003EBr\u00c3\u00a9das and postdoctoral research fellow Georg Heimel, who is now at the Humboldt University in Berlin, looked for changes in the work function of gold when they modified the chemical nature of the head group of the organic molecules in the self-assembled monolayer and the nature of the docking group, which directly connected the organic layer and metal. \n\u003C\/p\u003E\n\u003Cp\u003EThe study, published in the April 2007 issue of the journal \u003Cem\u003ENano Letters\u003C\/em\u003E, showed that changing the head group of the organic molecules located far from the surface and changing the docking group provided two nearly independent ways to modify the metal work function.\n\u003C\/p\u003E\n\u003Cp\u003EWhile studying two metal substrates - gold and silver - the researchers found that even though the chemical interface between the metal and thiol-based self-assembled monolayer were different, the organic-covered metals had virtually identical work functions.\n\u003C\/p\u003E\n\u003Cp\u003EPostdoctoral research fellow Pavel Paramonov, who is now an assistant research professor at the University of Akron, expanded the original work to model the interface between a self-assembled monolayer and indium tin oxide, the conducting material commonly used as the transparent electrode in liquid crystal displays and organic light-emitting diodes. \n\u003C\/p\u003E\n\u003Cp\u003E\u0022Researchers frequently cover the hydrophilic indium tin oxide surface with a self-assembled monolayer containing a hydrophobic subgroup pointing away from the surface, providing much better adherence and compatibility with the active organic layer that comes on top,\u0022 said Br\u00c3\u00a9das.\n\u003C\/p\u003E\n\u003Cp\u003EThe cover layer also prevents the indium from diffusing into the active organic layer and degrading the device, but adding this layer also provides a way to fine-tune the work function. \n\u003C\/p\u003E\n\u003Cp\u003EWith funding from the Solvay Group, Paramonov modeled the indium tin oxide surface, which was a complex task because indium tin oxide is not stoichiometric - every vendor\u0027s indium tin oxide is somewhat different. Then he modeled the binding of a self-assembled monolayer of phosphonic acid to the indium tin oxide surface. Paramonov\u0027s first goal was to determine how the oxygen and phosphorus atoms of the self-assembled monolayer bind to the indium tin oxide surface. \n\u003C\/p\u003E\n\u003Cp\u003EIn collaboration with Seth Marder, a professor in the Georgia Tech School of Chemistry and Biochemistry, and Neal Armstrong, a professor in the Department of Chemistry at the University of Arizona, the researchers were able to characterize the main binding modes of the phosphonic acid molecules on indium tin oxide. This work has led to further research characterizing the impact of the self-assembled monolayer on the indium tin oxide work function, according to Br\u00c3\u00a9das.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022More theoretical work needs to be done to study conducting oxides used as transparent electrodes in organic solar cells and organic transistors,\u0022 added Br\u00c3\u00a9das. \u0022On the experimental side, the quality of the self-assembled monolayer coverage also needs to be improved.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EResearchers usually design devices with potentially well-aligned energy levels when the layers are measured individually, but they should be examining the layers when they are attached, according to Br\u00c3\u00a9das. This is because the reorganization of the chemical, electronic and geometric structures of the two layers at the interface has a major impact on the overall device characteristics.\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\n\u003C\/strong\u003E\u003C\/p\u003E\n\u003Cp\u003EMedia Relations Contacts: Abby Vogel (404-385-3364); E-mail: (\u003Ca href=\u0022mailto:avogel@gatech.edu\u0022\u003Eavogel@gatech.edu\u003C\/a\u003E) or John Toon (404-894-6986); E-mail: (\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E).\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003ETechnical Contact:\u003C\/strong\u003E Jean-Luc Br\u00c3\u00a9das (404-385-4986); E-mail: (\u003Ca href=\u0022mailto:jean-luc.bredas@chemistry.gatech.edu\u0022\u003Ejean-luc.bredas@chemistry.gatech.edu\u003C\/a\u003E).\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EWriter:\u003C\/strong\u003E Abby Vogel\n\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"Organic-based devices, such as organic light-emitting diodes, require a transparent conductive layer with a high work function, meaning it promotes injection of electron holes into an organic layer to produce more light. New research provides insight into factors that influence the injection efficiency.","format":"limited_html"}],"field_summary_sentence":[{"value":"Models developed to improve efficiency of organic-based devices"}],"uid":"27206","created_gmt":"2008-07-08 00:00:00","changed_gmt":"2016-10-08 03:03:19","author":"Abby Vogel Robinson","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2008-07-08T00:00:00-04:00","iso_date":"2008-07-08T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"71134":{"id":"71134","type":"image","title":"Jean-Luc Br\u00c3\u00a9das","body":null,"created":"1449177348","gmt_created":"2015-12-03 21:15:48","changed":"1475894630","gmt_changed":"2016-10-08 02:43:50"},"71135":{"id":"71135","type":"image","title":"Jean-Luc Bredas","body":null,"created":"1449177348","gmt_created":"2015-12-03 21:15:48","changed":"1475894630","gmt_changed":"2016-10-08 02:43:50"}},"media_ids":["71134","71135"],"related_links":[{"url":"http:\/\/www.chemistry.gatech.edu\/","title":"School of Chemistry and Biochemistry"},{"url":"http:\/\/www.chemistry.gatech.edu\/faculty\/Marder\/","title":"Seth Marder"},{"url":"http:\/\/www.chemistry.gatech.edu\/faculty\/bredas\/","title":"Bio of Jean-Luc Bredas"},{"url":"http:\/\/dx.doi.org\/10.1021\/nl0629106","title":"Nano Letters paper"}],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[{"id":"141","name":"Chemistry and Chemical Engineering"},{"id":"145","name":"Engineering"},{"id":"149","name":"Nanotechnology and Nanoscience"},{"id":"135","name":"Research"}],"keywords":[{"id":"7308","name":"acid"},{"id":"7300","name":"assembled"},{"id":"7295","name":"conduct"},{"id":"7297","name":"conductive"},{"id":"7294","name":"diode"},{"id":"1362","name":"efficiency"},{"id":"7309","name":"electrode"},{"id":"6884","name":"electron"},{"id":"7293","name":"emitting"},{"id":"2185","name":"gold"},{"id":"7306","name":"hydrophilic"},{"id":"7305","name":"hydrophobic"},{"id":"7302","name":"indium"},{"id":"7296","name":"injection"},{"id":"2815","name":"interface"},{"id":"7292","name":"light"},{"id":"7082","name":"metal"},{"id":"647","name":"metallic"},{"id":"7301","name":"monolayer"},{"id":"2289","name":"organic"},{"id":"7304","name":"oxide"},{"id":"7307","name":"phosphonic"},{"id":"1744","name":"quantum"},{"id":"170868","name":"self"},{"id":"169009","name":"silver"},{"id":"7289","name":"thiol"},{"id":"7303","name":"tin"}],"core_research_areas":[],"news_room_topics":[],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cstrong\u003EAbby Robinson\u003C\/strong\u003E\u003Cbr \/\u003EResearch News and Publications\u003Cbr \/\u003E\u003Ca href=\u0022http:\/\/www.gatech.edu\/contact\/index.html?id=avogel6\u0022\u003EContact Abby Robinson\u003C\/a\u003E\u003Cbr \/\u003E\u003Cstrong\u003E404-385-3364\u003C\/strong\u003E","format":"limited_html"}],"email":["abby@innovate.gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}