Bernard Kippelen

Azo dye-doped photorefractive polymers

The studies of the photorefractive properties of the two polymer composites based on poly(N-vinylcarbazole) (PVK) are reported. The polymers were obtained by doping PVK with 2,4,7 trinitro-9- fluorenone as a sensitizer agent and two different azo dyes as nonlinear chromophores. Best results were obtained for the polymer doped with 2,5-dimethyl-4-p-nitrophenylazoanisole, which showed a maximum diffraction efficiency of 34% at 40 V/micrometers external electric field strength in 105 micrometers thick samples. The influence of different geometries of the hologram writing- retrieval on the diffraction efficiency is described. Net amplification of one of the writing beams in two-beam coupling within the material has been observed. Recording of the holograms of 2-dimensional objects in real time has been demonstrated with good resolution and image brightness. All the results were obtained with a low power visible laser diode emitting at 675 nm.

Molecular self-assembly approaches to multilayer organic light-emitting-diode structures

An attractive and challenging approach to the construction of robust, structurally precise thin film materials with large second-order optical nonlinearities or electroluminescent characteristics is the covalent self-assembly of arrays of tailored molecular building blocks. In this contribution, we discuss the implementation of self-limiting siloxane self- assembly processes to achieve the fabrication of structurally regular organic LED (OLED) devices. Areas surveyed include: (1) the use of layer-by-layer self-assembly for ITO electrode modification/passivation/hole-electron carrier balancing in vapor deposited devices, (2) the synthesis of chlorosilane- functionalized precursor molecules for hole transport (HTL), emissive layer (EML), and electron transport layer (ETL) self- assembly, (3) the physicochemical and microstructural characterization of the HTL self-assembly process employing a triarylamine precursor, (4) the fabrication and characterization of a hybrid self-assembled + vapor deposited two-layer OLED, (5) the fabrication and characterization of a fully self-assembled two-layer OLED.

Molecular Self-Assembly Routes to Optically Functional Thin Films: Electroluminescent Multilayer Structures

This contribution describes the use of layer-by-layer self-limiting siloxane chemisorption processes to self-assemble structurally regular multilayer organic LED (OLED) devices. Topics discussed include: (1) the synthesis of silyl-functionalized precursor molecules for hole transport layer (HTL), emissive layer (EML), and electron transport layer (ETL) self-assembly, (2) the use of layer-by-layer self-assembly for ITO electrode modification/passivation/hole-electron balancing in a vapor-deposited device, (3) the microstructure/chemical characterization of HTL self-assembly using a prototype triarylamine precursor, (4) fabrication and properties of a hybrid self-assembled + vapor deposited two-layer LED, and (5) fabrication and properties of a fully self-assembled two-layer OLED.

Efficient Green and Blue Electrophosphorescent Light-Emitting Diodes using a Combination of Solution and Vacuum-Processed Materials

The performance of organic light-emitting diode devices with a spin-coated hole-transporting layer and a thermally deposited emissive layer consisting of a bis-sulfone small molecule, as a host for the blue phosphorescent emitter will be presented.