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Charge separation in localized and delocalized electronic states in polymeric semiconductors

Title data

Köhler, Anna ; dos Santos, D. A. ; Beljonne, David ; Shuai, Z. ; Bredas, J.-L. ; Holmes, Andrew B. ; Kraus, Andreas ; Müllen, Klaus ; Friend, Richard H.:
Charge separation in localized and delocalized electronic states in polymeric semiconductors.
In: Nature. Vol. 392 (1998) . - pp. 903-906.
ISSN 1476-4687
DOI: https://doi.org/10.1038/31901

Abstract in another language

Conjugated polymers such as poly(p-phenylene vinylene)s (PPVs) allow low-cost fabrication of thin semiconducting films by solution processing onto substrates. Several polymeric optoelectronic devices have been developed in recent years, including field-effect transistors1, light-emitting diodes2, photocells3,4 and lasers5. It is still not clear, however, whether the description of electronic excitations in these materials is most appropriately formulated within a molecular or semiconductor (band-theory) picture. In the former case, excited states are localized and are described as excitons; in the latter they are delocalized and described as free electron–hole pairs. Here we report studies of the electronic states associated with optical excitations in the visible and ultraviolet range for the conjugated polymer poly(2-methoxy-5-(2'-ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV), by means of photocurrent measurements and quantum-chemical calculations. We find several photocurrent spectral features between 3 and 5 eV which are coupled with bands in the absorption spectrum. On modelling the excited states in this energy range, we have discovered an important feature that is likely to be general for materials composed of coupled molecular units: that mixing of delocalized conduction- and valence-band states with states localized on the molecular units produces a sequence of excited states in which positive and negative charges can be separated further at higher energies. In other words, these excited states facilitate charge separation, and provide a conceptual bridge between the molecular (localized) and semiconductor (delocalized) pictures.

Further data

Item Type: Article in a journal
Refereed: No
Institutions of the University: Faculties > Faculty of Mathematics, Physics und Computer Science > Department of Physics > Lehrstuhl Experimentalphysik II - Optoelektronik weicher Materie > Lehrstuhl Experimentalphysik II - Optoelektronik weicher Materie - Univ.-Prof. Dr. Anna Köhler
Faculties
Faculties > Faculty of Mathematics, Physics und Computer Science
Faculties > Faculty of Mathematics, Physics und Computer Science > Department of Physics
Faculties > Faculty of Mathematics, Physics und Computer Science > Department of Physics > Lehrstuhl Experimentalphysik II - Optoelektronik weicher Materie
Result of work at the UBT: No
DDC Subjects: 500 Science > 530 Physics
Date Deposited: 18 Mar 2015 10:11
Last Modified: 16 Apr 2018 11:32
URI: https://eref.uni-bayreuth.de/id/eprint/8481