Rolf Wehrmann

Electrochromic Window Based on Conducting Poly(3,4‐ethylenedioxythiophene)–Poly(styrene sulfonate)

A short survey of technological aspects of electrochromism with various electroactive species is given. Different approaches with inorganic and organic materials have been pursued in the past. So far widespread usage of this technology for large area applications has not been achieved. Nevertheless one major technical product, self-darkening rear-view mirrors for cars, is already well established. This article reviews some research results on electroactive polythiophenes, especially poly(3,4-alkylenedioxythiophenes). Some promising results with the commercially available electrically conducting polymer Baytron P (PEDT/PSS) are presented. It is demonstrated that an all solid-state electrochromic multilayer assembly based on a polymeric electrochromic material might be close to technical realization. The coating of large area substrates with aqueous poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) dispersion can be a way to an economically viable product.

PEDT/PSS for efficient hole-injection in hybrid organic light-emitting diodes

Light-emitting diodes have been prepared by depositing three organic layers successively by spin-coat and evaporation techniques. The first layer of PEDT/PSS smoothens the ITO surface, reduces the probability of electrical shorts and is beneficial for a high overall yield of the operating devices. Above all, this layer promotes hole-injection as an important parameter for higher efficiencies and prolonged operation life. The second layer of spin-coated dendritic phenylamines (TDAPB) with high glass transition temperature modulates the injection of holes into the emitting layer, formed by evaporated Alq. By comparing characteristics and operation lifetime data of devices with and without PEDT/PSS it is shown that the combination of polymeric and monomeric organic layers leads to highly efficient devices, opening new ways to modify device architectures.

Gallium Complexes in Three‐Layer Organic Electroluminescent Devices

Organic light-emitting diodes fabricated by subsequently spin-coating two layers-a hole-transporting followed by a metal chelate emissive layer - onto poly(3,4-ethylene-dioxythiophene)/poly(styrenesulfonate) are presentedfor the first time. The electron-hole recombination occurs in a layer consisting of Ga complexes (see Figure), which exhibit high fluorescence quantum yields, and their emission spectra are blue-shifted relative to that of tris(8-hydroxyquinoline) aluminum. By doping this spin-coated emission layer with fluorescent emitters the emission band can be shifted within the visible spectral range.

Polyesters and polyurethanes as prepolymerized materials for Langmuir-Blodgett films: Preparation and characterization of multilayers

Abstract Two new types of amphiphilic polymers, namely polyesters and polyurethanes, capable of forming monolayers at an air-water interface were synthesized. The polyesters were obtained by the condensation of both long-chain substituted diols and diesters with available materials. The amphiphilic polyurethanes were prepared by polyaddition of long-chain diols and common diisocyanates. Pressure-area isotherms show the formation of a more-or-less liquid- analogous state. Y-mode Langmuir-Blodgett multilayers of these preformed polymers can be transferred to rigid substrates with a constant transfer ratio. In polyester and polyurethane multilayers, the aliphatic side-chains are perpendicular to the film as evidenced by ellipsometric and X-ray measurements of film thickness and orientation.