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Electrophosphorescence from substituted poly(thiophene) doped with iridium or platinum complex
Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics . Linköping University, The Institute of Technology.
Department of Organic Chemistry and Polymer Technology, Chalmers University of Technology, Göteborg, Sweden.
Department of Chemistry, University of Southern California, Los Angeles, USA.
Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics . Linköping University, The Institute of Technology.
2004 (English)In: Thin Solid Films, ISSN 0040-6090, Vol. 468, no 1-2, 226-233 p.Article in journal (Refereed) Published
Abstract [en]

Electrophosphorescence has been observed in doped polythiophene light-emitting diodes (LEDs) with poly(3-methyl-4-octylthiophene) [PMOT] as host and the phosphorescent compounds bis(2-phenylbenzothiazole) iridium acetylacetonate (BTIr) or platinum(II) 2,8,12,17-tetraethyl-3,7,13,18-tramethyl porphyrin (PtOX) as guest. The photoluminescence (PL) and electroluminescence (EL) of host–phosphorescent guest blends PMOT:BTIr (or PMOT:PtOX) showed the existence of energy transfer from host to guest, which were guest concentration-dependent. At a certain guest concentration, emission from host PMOT was completely quenched in both blends based LEDs, and this gave rise to electrophosphorescence. The PL from host PMOT in the PMOT:BTIr blend film could not be quenched completely but was totally quenched in PMOT:PtOX. This implies a more efficient energy transfer from PMOT to PtOX than that from PMOT to BTIr under optical excitation. Comparison of PL and EL showed that the mechanism of exciton formation at the guest site under electrical excitation was not identical for these two systems. Energy transfer was a dominating route for exciton formation in PMOT:PtOX-based LEDs; charge trapping effect additionally contributed to the formation of exciton at BTIr in PMOT:BTIr-based LEDs. This study demonstrates a new direction in which polythiophene can be a candidate as a host to realize electrophosphorescence in polymer light-emitting diodes (PLEDs). Authors further indicate that to optimize the performance of the polythiophe/phosphorescent complexes, LEDs proper polythiophenes with large bang gap are needed.

Place, publisher, year, edition, pages
2004. Vol. 468, no 1-2, 226-233 p.
Keyword [en]
Polymer LED, Electrophosphorescence, Energy transfer, Quenching of luminescence, Polythiophene, Phosphorescent complex
National Category
Natural Sciences
URN: urn:nbn:se:liu:diva-13887DOI: 10.1016/j.tsf.2004.05.095OAI: diva2:22129
Available from: 2006-07-07 Created: 2006-07-07 Last updated: 2009-10-05
In thesis
1. Surface Energy Patterning and Optoelectronic Devices Based on Conjugated Polymers
Open this publication in new window or tab >>Surface Energy Patterning and Optoelectronic Devices Based on Conjugated Polymers
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The work presented in this thesis concerns surface energy modification and patterning of the surfaces of conjugated polymers. Goniometry and Wilhelmy Balance techniques were used to evaluate the surface energy or wettability of a polymer’s surface; infrared reflectionabsorption spectroscopy (IRAS) was used to analyse the residuals on the surface as modified by a bare elastomeric stamp poly(dimethylsiloxane) (PDMS). The stamp was found to be capable of modifying a polymer surface. Patterning of a single and/or double layer of conjugated polymers on the surface can be achieved by surface energy controlled dewetting. Modification of a conjugated polymer film can also be carried out when a sample is subjected to electrochemical doping in an aqueous electrolyte. The dynamic surface energy changes during the process were monitored in-situ using the Wilhelmy balance method.

This thesis also concerns studies of conjugated polymer-based optoelectronics, including light-emitting diodes (PLEDs), that generate light by injecting charge into the active polymer layer, and solar cells (PSCs), that create electrical power by absorbing and then converting solar photons into electron/hole pairs. A phosphorescent metal complex was doped into polythiophene to fabricate PLEDs. The energy transfer from the host polymer to the guest phosphorescent metal (iridium and platinum) complex was studied using photoluminescence and electroluminescence measurements performed at room temperature and at liquid nitrogen temperature. PSCs were prepared using low-bandgap polyfluorene copolymers as an electron donor blended with several fullerene derivatives acting as electron acceptors. Energetic match is the main issue affecting efficient charge transfer at the interface between the polymers and the fullerene derivatives, and therefore the performance of the PSCs. Photoluminescence, luminescence quenching and the lowest unoccupied molecular orbital (LUMO) together with the highest occupied molecular orbital (HOMO) of the active materials in the devices were studied. A newly synthesized fullerene, that could match the low-bandgap polymers, was selected and used as electron acceptor in the PSCs. Photovoltaic properties of these PSCs were characterised, demonstrating one of the most efficient polymer:fullerene SCs that generate photocurrent at 1 μm.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi, 2006
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 996
Surface energy modification, Patterning, Dewetting, Conjugated polymer, plastic solar cell, Low bandgap, Electron acceptors and donors
National Category
Physical Sciences
urn:nbn:se:liu:diva-7065 (URN)91-85497-00-2 (ISBN)
Public defence
2006-03-10, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
On the day of the defence the status of article number III was Manuscript and article VII was Accepted.Available from: 2006-07-07 Created: 2006-07-07 Last updated: 2009-10-05

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