Thomas Granlund

Trapping Light in Polymer Photodiodes with Soft Embossed Gratings

Increasing the conversion efficiency is very important in photovoltaic devices, as is cheap and simple technology. Here is demonstrated a soft embossing technique for printing a submicrometer grati ...

Interference phenomenon determines the color in an organic light emitting diode

We report on electroluminescence from two-layer organic diodes made of poly(3-methyl-4-octylthiophene) and 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,2,4-oxadiazole films between electrodes of indium tin oxide and Ca/Al. The diodes emitted light in the green-blue range; the electroluminescence spectra varied between diodes with different thicknesses of the polymer and molecular layers. The optical phenomena were simulated with a model accounting for interference effects; simulated results showed that the electroluminescence from the organic diode can be due neither to luminescence of the polymer nor of the molecular layer. These model simulations, together with electrochemical measurements, can be interpreted as evidence for an indirect optical transition at the polymer/molecule interface that only occurs in a strong electric field. We label this transition an electroplex.

A polythiophene microcavity laser

We report photopumped lasing in a microcavity device with a polythiophene layer as the emitter. These microcavity devices are built by joining two polymer coated dielectric mirrors at elevated temperature. When photopumping the film, a lasing threshold is observed at 120 nJ/cm(2). Comparative studies with fast pump-probe spectroscopy of thin polythiophene films and the same polymer in photopumped lasing studies, indicate that the gain coefficient is 80 +/- 20 cm(-1), and that the exciton concentration is 2 X 10(17) cm(-3) at the lasing transition, well below the exciton-exciton recombination level

Determination of the emission zone in a single-layer polymer light-emitting diode through optical measurements

We study the emission zone in a single-layer polymer light-emitting diode. The emission zone is found by studying the angular distribution of the electroluminescence. The emission is modeled by acc ...

Lasing in a microcavity with an oriented liquid-crystalline polyfluorene copolymer as active layer

Lasing in a microcavity with an oriented liquid-crystalline polyfluorene copolymer as active layer

Polymer light-emitting diodes placed in microcavities

The use of resonant optical microcavities to influence the emission properties of conjugated polymer light-emitting diodes (LEDs) is reported. The microcavities, which are built using metallic mirrors and polymeric spacers, incorporate polymer LEDs in between the mirrors. We report experimental results of polymer LEDs based on substituted polythiophenes. The effects include substantial narrowing of the spectral width of the emitted light, enhancement of the emission at the microcavity resonance, and coupling of two emission processes to different resonance modes in the same cavity.

Optical emission from confined poly(thiophene) chains

We discuss the stages of the luminescence processes in substituted and soluble poly(thiophenes), using results from determinations of absolute quantum yields of photoluminescence, fast pump-probe experiments and microcavity devices. Enhancement of the quantum yield of photoluminescence, with poly(thiophenes) in the solid state, call be obtained by dispersing the conjugated chain in a molecularly dispersed polymer blend, or by adding side chains designed for forcing the conjugated main chains apart. At the wavelength of stimulated emission, we observe a narrow bandwidth emission in the high-Q one-dimensional microcavity devices prepared by sandwiching two dielectric mirrors around a thin polymer film, A strong enhancement of the power efficiency is observed at a pump power of 1 mu W/cm(2), but does not conclusively show lasing characteristics

Lasing in substituted polythiophene between dielectric mirrors

We report photopumped lasing in a microcavity device with a polythiophene layer as emitter. The microcavity is made of a polymer film between two dielectric Bragg reflecting mirrors (DBR). The:micr ...

Luminescence probing of crystallization in a polymer film

We report studies of a thin film multilayer stack including a highly emissive substituted polythiophene, poly[3-(2,5-dioctylphenyl)thiophene]. Analysis of the photoluminescence spectra revealed an ...