Synthesis and self-organization of PPV-based block copolymers for photonic applications

Rod-coil block copolymers have been synthesized with the objective of enhancing the photovoltaic efficiency by the incorporation of both donor and acceptor components in a molecular architecture that is self-structuring. Block copolymers were obtained by using an end-functionalized rigid-rod block of poly(2,5-dioctyloxy-1,4-phenylenevinylene) (PPV) as a macroinitiator for the nitroxide-mediated controlled radical polymerization of a flexible, styrene-based block. Under suitable conditions the formation of honeycomb structures by PPV-block-polystyrene (pPV-b-PS) is observed. The honeycomb structure consists of a 2-dimensional array of spherical air holes with an inner diameter of 3 - 5 µm in a polymeric film, which results in ~ 6.5 million hexagonally packed holes per square centimeter. The application of these structures as templates for highly ordered functional patterns is demonstrated by evaporating aluminum on this regularly structured surface and subsequently washing away the polymer.

Energy level alignment at the conjugated phenylenevinylene oligomer/metal interface

In this letter we report an investigation of the interfacial electronic structure formed by metals and conjugated oligomers using ultraviolet photoelectron spectroscopy. Au and Ag were used as metal substrates for two five-ring phenylenevinylene oligomers: unsubstituted p-bis[(p-styryl)styryl]benzene (P5V4) and the analogous oligomer with 2-methoxy-5-(2’-ethyl-hexyloxy) substitution on the central ring (MEH-P5V4). We found for all interfaces a lowering of the energy levels of the organic overlayer by 0.4–1.2 eV. Remarkably, this energy lowering, presumably due to interface dipole layers, was always such as to keep the hole injection barrier nearly constant and therefore at most weakly sensitive to the work function of the metal or the ionization potential of the oligomer.