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Does Excess Energy Assist Photogeneration in an Organic Low-Bandgap Solar Cell?

Title data

Hahn, Tobias ; Geiger, Johannes ; Blase, Xavier ; Duchemin, Ivan ; Niedzialek, Dorota ; Tscheuschner, Steffen ; Beljonne, David ; Bässler, Heinz ; Köhler, Anna:
Does Excess Energy Assist Photogeneration in an Organic Low-Bandgap Solar Cell?
In: Advanced Functional Materials. Vol. 25 (February 2015) Issue 8 . - pp. 1287-1295.
ISSN 1616-3028
DOI: https://doi.org/10.1002/adfm.201403784

Abstract in another language

The field dependence of the photocurrent in a bilayer assembly is measured with the aim to clarify the role of excess photon energy in an organic solar cell comprising a polymeric donor and an acceptor. Upon optical excitation of the donor an electron is transferred to the acceptor forming a Coulomb-bound electron–hole pair. Since the subsequent escape is a field assisted process it follows that photogeneration saturates at higher electric fields, the saturation field being a measure of the separation of the electron–hole pair. Using the low bandgap polymers, PCDTBT and PCPDTBT, as donors and C60 as acceptor in a bilayer assembly it is found that the saturation field decreases when the photon energy is roughly 0.5 eV above the S1–S0 0–0 transition of the donor. This translates into an increase of the size of the electron-hole-pair up to about 13 nm which is close to the Coulomb capture radius. This increase correlates with the onset of higher electronic states that have a highly delocalized character, as confirmed by quantum-chemical calculations. This demonstrates that accessing higher electronic states does favor photogeneration yet excess vibrational energy plays no role. Experiments on intrinsic photogeneration in donor photodiodes without acceptors support this reasoning.

Further data

Item Type: Article in a journal
Refereed: Yes
Keywords: charge–transfer states;
donor–acceptor;
field-dependent photogeneration;
organic photovoltaics
Institutions of the University: Faculties > Faculty of Mathematics, Physics und Computer Science > Department of Physics > Chair Experimental Physics II - Optoelectronics of Soft Matter > Chair Experimental Physics II - Optoelectronics of Soft Matter - 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 > Chair Experimental Physics II - Optoelectronics of Soft Matter
Result of work at the UBT: Yes
DDC Subjects: 500 Science > 530 Physics
Date Deposited: 19 Feb 2015 07:46
Last Modified: 01 Feb 2021 09:56
URI: https://eref.uni-bayreuth.de/id/eprint/7166