Emiel G. J. Staring

The X-ray structure and MNDO calculations of α-terthienyl: A model for polythiophenes

Abstract The X-ray structure of α-terthienyl reveals two identical, crystallographically-independent molecules in the unit cell. Neighbouring thiophene moieties in α-terthienyl are placed antiparallel, while the molecule is almost planar, with torsional angles between the rings of about 6 – 9°. MNDO calculations of α-terthienyl show that great care should be taken in using calculations of this type for geometrical optimizations of polythiophenes.

Photo- and electroluminescence efficiency in poly(dialkoxy-p-phenylenevinylene)

Abstract This paper presents the dependence of luminescence efficiency on the degree of conjugation for a soluble poly(dialkoxy- p -phenylenevinylene), comparing the photoluminescence yields with the electroluminescence yields. Photoluminescence efficiency increases with the fraction of non-conjugated units for polymers both in the solid state and in solution. The highest external electroluminescence efficiency measured is 1.4% (photons/electron) for a polymer having approximately 10% non-conjugated units. Electroluminescence efficiency depends not only on the radiative recombination efficiency of the emitting material but also on carrier transport into and within the material.

Chemical vapour deposition of poly(1,4-phenylenevinylene) films

Abstract In this paper we present a chemical vapour deposition (CVD) method for the preparation of thin films of poly(1,4-phenylenevinylene) (PPV) on various substrates. The CVD process results in the initial formation of a non-conjugated precursor polymer film, which can be thermally converted into PPV. The films were characterized by various techniques. We also show that these PPV films can be used to fabricate polymer light-emitting diodes (LEDs). A maximum efficiency of 0.002% (photons/electron, external) was achieved.

Electroluminescence and photoluminescence efficiency of poly(p-phenylenevinylene) derivatives

Abstract Alkoxy, alkyl, and cyano derivatives of poly( p -phenylenevinylene) [PPV] are used as the emissive layers in light-emitting diodes [LEDs] to obtain luminescence from red to blue. We present the luminescence efficiency for these soluble PPV derivatives. comparing the photoluminescence [PL] yields with the electroluminescence [EL] yields. PL efficiency increases with the fraction of non-conjugated units. EL efficiency depends not only on the radiative recombination efficiency of the emitting material but also on carrier transport to and within the material. Efforts to improve the efficiency and long term stability of these polymer LEDs are challenged by efficient and balanced carrier injection.

Schottky effect at a metal‐polymer interface

We report the observation of the Schottky effect at the interface between a metal and a semiconducting polymer by means of internal photoemission spectroscopy. The bias dependence of the barrier provides information on the electrical properties of the polymer.

Efficient modal dispersion phase‐matched frequency doubling in poled polymer waveguides

We report the design, manufacture, and characterization of poled polymer multilayer waveguides for frequency doubling. Phase matching is obtained by using modal dispersion between the zeroth‐order fundamental lightwave and the first‐order second‐harmonic wave. By incorporating a very thin high refractive index satellite layer, the phase‐match condition can be fulfilled with concomitant large overlap between the two waves, resulting in efficient doubling.

Internal photoemission studies of metal/polymer interfaces

Abstract Internal photoemission is shown to be a valuable technique for studying electronic properties of buried metal/semiconducting polymer interfaces. The height of the observed barriers gives information on the nature of the interface, whereas the electric field dependence of the barrier height reflects important polymer properties. It is found that the barrier height is not determined by a simple electron affinity rule but by a high surface density of states.

The effect of broken conjugation and aggregation on photo-induced charge separation on polyphenylenevinylene chains

Abstract Flash photoexcitation of dilute solutions of fully conjugated poly(2,5-dialkoxyphenylenevinylene)s results in a transient change in the microwave conductivity. Gel formation resulting from aggregation of polymer chains in some of the solutions leads to an increase in the photo-induced conductivity. The effects are attributed to the formation of mobile charge carriers (polaron pairs) on a single polymer chain in the case of the solutions, and on separate chains via interchain charge transfer in the gel. Mobile charge carrier formation is strongly reduced by the incorporation of even a few percent of non-conjugated ethylidene units in the polymer backbone

State-of-the-art: in Polymer Light-Emitting Diodes NEOME Polymer LED Mini Symposium (15–17 September 1993, Eindhoven, The Netherlands)

Abstract A symposium focused on recent progress in the field of polymer light-emitting diodes was held in Eindhoven during the period 15–17 September 1993. The following is a brief summary of highlights of the symposium. There will be no published proceedings.

Linear optical properties of frequency doubling polymers

Measurements of linear optical properties of methylmethacrylate copolymers with non-linear optical 4-alkoxy-4′-alkylsulfone stilbene side-chains are presented. From there two methods for phase matching are discussed; one aiming to equalize the refractive indices of the fundamental and the second harmnic wave, the other to suppress the destructive character of the interference. The matter of photo stability of frequency doubling polymers is also discussed.