| 1. |
- Granlund, T, et al.
(författare)
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Determination of the emission zone in a single-layer polymer light-emitting diode through optical measurements
- 2001
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Ingår i: Journal of Applied Physics. - 0021-8979 .- 1089-7550. ; 89:11, s. 5897-5902
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Tidskriftsartikel (refereegranskat)abstract
- 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 accounting for optical interference. We account for birefringence of the anode layer in our model. The active polymer was, however, found to be isotropic. The anode consists of a single-layer of the conducting polymer complex poly(3,4-ethylenedioxythiophene) and poly(styrene sulfonate) (PEDOT-PSS), with enhanced conductivity. As a cathode we use plain aluminum. By using only PEDOT-PSS we avoid having a thin metal layer or indium-tin-oxide as the anode in the path of the escaping light. The active material is a substituted polythiophene with excellent film forming properties. A comparison between the experimental and calculated angular distribution of light emission from a single-layered polymer light-emitting diode was shown to be in good agreement for the spectral region studied. By assuming a distribution of the emission zone, we deduce the position as well as the width of the zone. (C) 2001 American Institute of Physics.
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| 2. |
- Granlund, T, et al.
(författare)
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Luminescence probing of crystallization in a polymer film
- 2000
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Ingår i: Journal of Applied Physics. - 0021-8979 .- 1089-7550. ; 87:12, s. 8549-8556
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Tidskriftsartikel (refereegranskat)abstract
- 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 inhomogeneous polymer film. X-ray diffraction studies attribute the existence of an inhomogeneous film as originating from crystallization of the polymer. We used the interference effect of light to detect the region of crystallization in the film. Photoluminescence and absorption were redshifted upon crystallization and displayed an enhanced vibronic structure. Comparison between calculated and measured photoluminescence shows that the crystallization starts from the top of the film and not from the supporting substrate. (C) 2000 American Institute of Physics. [S0021- 8979(00)08112-3].
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| 3. |
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| 4. |
- Inganäs, Olle, et al.
(författare)
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Optical emission from confined poly(thiophene) chains
- 1998
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Ingår i: Optical materials (Amsterdam). - : Elsevier. - 0925-3467 .- 1873-1252. ; 9:1-4, s. 104-108
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Tidskriftsartikel (refereegranskat)abstract
- 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. (C) 1998 Elsevier Science B.V.
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| 5. |
- Johansson, D.M., et al.
(författare)
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Synthesis and characterisation of polyfluorenes with light-emitting segments
- 2001
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Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 121:1-3, s. 1761-1762
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Tidskriftsartikel (refereegranskat)abstract
- We present the synthesis and characterisation of two copolymers. They consists of poly(9-hexyl-9-(2'-ethylhexyl)fluorene) (HEH-PF) with a small amount of another polymer with a narrow band-gap. The synthetic route was designed to allow the incorporation of only one low band-gap segment per polymer chain. Photoluminescence measurements showed that energy transfer from the PF-segments to the low band-gap segments, did occur. In the solid state, all emissions were detected from the low band-gap segments with photoluminescence quantum yields up to 68%. One copolymer showed a low threshold for lasing (2 µJ/cm2) in a microcavity device.
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| 6. |
- Johansson, DM, et al.
(författare)
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Synthesis and characterization of polyfluorenes with light-emitting segments
- 2001
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Ingår i: Macromolecules. - 0024-9297 .- 1520-5835. ; 34:6, s. 1981-1986
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Tidskriftsartikel (refereegranskat)abstract
- Two new polymers consisting of poly(9-(2'-ethylhexyl)-9-hexylfluorene) (EHH-PF) with a small amount of substituted poly(p-phenylenevinylene) (PPV) segments have been synthesized and characterized. The synthetic route was designed to allow the incorporation of only one (or zero) PPV segments per polymer chain. Photoluminescence measurements showed that energy transfer from the PF segments to the more narrow band-gap PPV segments did occur, both in solution and in film. In the solid state, all emissions were detected from the PPV segments with photoluminescence quantum yields up to 68%. One of the polymers has been used as the active material in a microcavity laser device. The threshold for lasing is 2 muJ/cm(2).
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| 7. |
- Roman, LS, et al.
(författare)
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Trapping light in polymer photodiodes with soft embossed gratings
- 2000
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Ingår i: Advanced Materials. - 0935-9648 .- 1521-4095. ; 12:3, s. 189-
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Tidskriftsartikel (refereegranskat)abstract
- 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 grating with an elastomeric mold into an optically active polymer layer in a photovoltaic device (see Figure). The light trapping due to the grating pattern enhances the photoconversion efficiency by more than 25 % at normal light incidence (see also inside front cover).
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| 8. |
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