• Impact of Functionalized Polystyrenes as the Electron Injection Layer on Gold and Aluminum Surfaces: A Combined Theoretical and Experimental Study

      Papadopoulos, Theodoros A.; Li, Hong; Kim, Eung-Gun; Liu, Jie; Cella, James A.; Heller, Christian M.; Shu, Andrew; Kahn, Antoine; Duggal, Anil; Brédas, Jean-Luc; et al. (Wiley, 2014-06-06)
      At metal/organic interfaces, insertion of an organic monolayer can significantly modify the surface properties of the substrate, especially in terms of charge injection across the interface. Here, we study the formation of an insulating monolayer of morpholine or amine-functionalized polystyrene on Al(111) and Au(111) surfaces and its impact on surface work-function and charge injection. First principles calculations based on density functional theory have been carried out and point to a significant decrease of the work-function for the modified metal surfaces, in very good agreement with ultraviolet photoemission spectroscopy measurements performed on the Au(111) surface. In addition, a bilayer cathode consisting of a thin film of high work-function metal, such as Al and Au, and a layer of amine-functionalized polystyrene is also fabricated and tested in organic light-emitting diodes. Such bilayer structures exhibit substantially enhanced efficiency when compared to controls without the functionalized polymers. Our combined theoretical and experimental investigation gives insight into how a thin layer of a commodity polymer can be used to transform rather high work-function metals into high-performance cathodes providing efficient electron injection.