MSE Seminar Series: Deirdre OCarroll
Friday, November 14, 2014
Room 2108, Chemical and Nuclear Engineering Bldg.
301 405 5240
Disordered Plasmonic Electrodes for Thin Film Optoelectronics
Department of Materials Science and Engineering
Rutgers, The State University of New Jersey
Plasmonic electrodes, consisting of thin films of nanostructured metal, can exhibit a number of optical, electrical and morphological effects that can be exploited to improve performance parameters of organic thin-film optoelectronic devices. Here we investigate the use of two different types of disordered plasmonic back electrodes - nanoporous metal (NPM) films and continuous metal nanoparticle array (MNPA) films - for thin film organic light-emitting diodes (OLEDs) and organic photovoltaics. NPM with periodic arrays of sub-wavelength holes have attracted significant attention due to the discovery of extraordinary optical transmission (EOT) arising from surface plasmons supported by the NPM. Recently it has been found that NPM films can also exhibit a phenomenon called absorption-included transparency (AIT) in addition to EOT when thin-film absorber layers are applied to nanoporous metal. Interestingly, while EOT depends sensitively on periodicity of the nanopores, AIT occurs even for single pores and, therefore, does not require a periodic arrangement of the nanopores.
In this work we employ large-area disordered NPM back electrodes for light extraction and emission enhancement from light-emitting polymer layers for OLED applications. We find that while light-scattering by the nanoporous metal is highly dependent on pore diameter, enhancements in light emission from the polymer layer coatings do not correlate well with pore diameter. Photoluminescence emission intensity enhancements of up to 12 and 30 are found for the disordered NPM/polymer composites with pore depths of 50 and 100 nm, respectively (with pore diameter approximately constant), which we attribute to a combination of far-field scattering and AIT-type effects. In addition to NPM, we investigate the morphological and plasmonic mode contributions of MNPA to organic photovoltaic active layer performance. Using dark-field microscopy we find evidence that far-field scattering, interparticle electromagnetic coupling and surface plasmon polariton modes are supported by the MNPA electrodes and we discuss the importance of each mode type for thin-film optoelectronic applications.
About the Speaker:
Deirdre O'Carroll is an Assistant Professor in Materials Science and Engineering and Chemistry at Rutgers University since 2011. She obtained her B.E. (Elec. Eng., 2002) and PhD (Microelectronics, 2008) at University College Cork and the Tyndall National Institute, Ireland. From 2007 to 2009 she was a postdoctoral researcher in the Atwater Group at California Institute of Technology and in 2010 she completed an International Marie Curie Fellowship in the Ebbesen Group at the University of Strasbourg and CNRS. Research interests include: Photonic nanostructures, plasmonics, conjugated polymer nanostructures and organic optoelectronic devices.