Lewis Josiah Rothberg

Status of and prospects for organic electroluminescence

We review the device and materials science behind organic electroluminescent diodes made both using discrete evaporable molecules and spin-cast organic polymers. A great deal of progress has been made in improving the efficiencies and spectral properties of organic light-emitting diodes, and these are now adequate for many applications. More work is necessary to understand the stability and degradation of emissive and charge-transporting organics, but some systems have been shown to be stable for 10 4 hours at display brightness. Major challenges still face the community in terms of developing satisfactory systems design and processing techniques if organic electroluminescence is to realize either performance or economic advantages over technologies and significantly penetrate the display market. We present an analysis of the suitability of organic light-emitting diodes for various applications, and consider the materials and manufacturing obstacles that must be overcome.

Color variation with electroluminescent organic semiconductors in multimode resonant cavities

The range of possibilities in controlling the color of an organic semiconductor based light emitter diode (LED) by incorporating the active layers in a multimode Fabry–Perot cavity is demonstrated. The combination of carefully designed multimode microcavities and electroluminescent organic semiconductors makes possible the realization of mixed colors such as white, purple, etc. with a single LED. The parameters affecting the color include the total optical thickness of the device and the position of the electromagnetic‐field antinodes with respect to the location of the emitting dipoles. The electrical characteristics and quantum efficiency of such devices are also reported.

Microcavity effects in organic semiconductors

Microcavity structures containing hydroxyquinoline aluminum and diamine layers commonly used in electroluminescent devices are described. We show that it is possible to obtain emission at red, green, and blue wavelengths by changing the thickness of a polyimide filler layer in the cavity. The angular dependence of the emission wavelength and linewidth are reported and the implications for organic electroluminescent color displays are discussed.

ELECTRICALLY ACTIVE ORGANIC AND POLYMERIC MATERIALS FOR THIN-FILM-TRANSISTOR TECHNOLOGIES

Organic and polymeric materzials have seen a tremendous growth in research in the last five years as potential electroactive elements in thin-film-transistor (TFT) applications. These are driven by the increasing interest in flat-panel-display applications, for which organic and polymeric materials offer strong promise in terms of properties, processability, cost, and compatibility with eventual lightweight, flexible plastic displays. In this review we summarize the current status of our knowledge on the science of these organic and polymeric semiconducting materials. Most of these are based on linear thiophenes, especially a-hexathienyl, which has elicited by far the most attention. Mobility values in the 10 −2 –10 −1 cm 2 /Vs and especially source-drain current on/off ratios of up to 10 6 make this a highly promising potential alternative to amorphous silicon. Other thienyl compounds are also discussed, as are polymeric analogues. A brief discussion of technological potential, limitations, and problems that need to be overcome is given at the end.

Short-Lived Photoinduced Excitations in Trans-Polyacetylene

Abstract We report subpicosecond studies of the photoinduced transient midgap absorption in oriented trans-polyacetylene. Measurements of the response following above bandgap excitation are made with pump polarizations both parallel and perpendicular to the chain direction. We observe rapid formation and decay of charged soliton pairs in each of these configurations. When photoexciting perpendicular to the chains, however, we also observe long-lived absorption in the gap which we ascribe to polarons. These data can explain the observed behavior of the photoconductivity in trans−polyacetylene.

Nickel(II) Octaethylporphyrin: Conformational Dynamics, Ligand Binding and Release

We report time resolved Raman and absorption experiments to characterize excited state vibrational frequencies and ligand binding in Nickel(II) porphyrins.