Journal article
Photophysics properties of blue-emitting polymers
Synthetic metals, Vol.125(1), pp.55-63
11/02/2001
DOI: 10.1016/S0379-6779(01)00511-2
Abstract
We report on an extensive spectroscopic study of thin films of two blue-emitting π-conjugated polymers (PCP), namely ladder-type poly-
para-phenylene (mLPPP) and polyfluorene (PFO). In our work, we employed several continuous-wave (cw) spectroscopic techniques, such as absorption, photoluminescence (PL), photoinduced absorption (PA) and PA detected magnetic resonance (PADMR). We have obtained PA spectra measured over a very broad spectral range from 0.05 to 2.5
eV and identify PA bands related to triplet excitons and charged polarons, respectively. We found that the low energy polaron PA band, P
1 peaks at unusually low photon energy, indicative of small relaxation energy for polarons in these materials. Similar results were obtained for high-mobility, highly ordered films of regio-regular poly-hexyl-thiophene (RR-P3HT), where the polarons are delocalized in two dimensions. In fact, the P
1 band is so low that it overlaps in photon energy with the photoinduced infra-red active vibrations (IRAVs) in the PA spectrum, consequently, this leads to the formation of anti-resonances between IRAVs and the electronic band, which are sharp lines that appear as dips superimposed on the PA band.
The spin 1/2 PADMR technique takes advantage of the dependence of the polaron recombination rate on the spin state of the recombining pairs of polarons. The origin of the spin-dependent recombination rate is a considerable difference in nature between singlet and triplet excitons in polymers, which are the two possible by-products of oppositely charged polaron recombination. The motivation for the PADMR study is the great importance of spin-dependent formation cross-sections to commercial light emitting diodes (LED) application. These cross-sections directly determine the maximum possible electroluminescence quantum efficiency (ELQE) for LEDs that are made from these polymers. We found that the ELQE may approach 60% for the blue-emitting polymers.
Details
- Title: Subtitle
- Photophysics properties of blue-emitting polymers
- Creators
- M. Wohlgenannt - University of UtahZ. Valy Vardeny
- Resource Type
- Journal article
- Publication Details
- Synthetic metals, Vol.125(1), pp.55-63
- Publisher
- Elsevier B.V
- DOI
- 10.1016/S0379-6779(01)00511-2
- ISSN
- 0379-6779
- eISSN
- 1879-3290
- Language
- English
- Date published
- 11/02/2001
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984428683102771
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