Self-assembled conjugated polymer-surfactant-silica mesostructures and their integration into light-emitting diodes

摘要

A self-assembly process for the preparation of functional mesoscopically ordered semiconducting polymer-silica nanocomposite thin films is reported.The nanocomposites are prepared by introducing pre-synthesized semiconducting polymers into a tetrahydrofuran (THF)-water homogeneous sol solution containing silica precursor species and a surface-active agent.Depending on the concentration of the surface-active agent,it was possible to prepare materials with three different types of mesostructural order:i) a 2D hexagonal mesophase silica with conjugated polymer guest species incorporated within the hydrophobic cylinders organized in domains aligned parallel to the substrate surface plane;ii) a lamellar mesophase silica with the layers oriented parallel to the substrate surface and the conjugated polymer guest species incorporated in the hydrophobic layers;or iii) an apparent intermediate phase consisting of a mixture of the hexagonal and lamellar phases in addition to worm-like aggregates with no appreciable orientational order.The continuous through-film conductive pathway provided by the intermediate phase has allowed the integration of ordered semiconducting polymer-silica nanocomposites into opto-electronic devices.By comparison,the lamellar mesostructure prevents through-film conduction,with the result that no light emission occurs.Blue-,green- and red-emitting diodes comprising blue-emitting poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO),green-emitting poly(9,9-dioctylfluorenyl-2,7-diyl)-co-l,4-benzo-(2,1',3)-thiadiazole) (F8BT),and red-emitting poly[2-methoxy-5(2'-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEHPPV) confined within the 2D hexagonal silica nanostructure were fabricated with luminances of ca.3 cd m-2 at 15 V.Device performances provide criteria for optimizing the selection of synthesis chemistries,processing conditions,compositions,and structures,for light-emission properties sought.