Dresden 2009 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 41: Organic Photovoltaics III

CPP 41.10: Talk

Friday, March 27, 2009, 12:45–13:00, ZEU 222

The nature of charge transfer excitons in conjugated polymer-fullerene blends — •Ilka Kriegel, Enrico Da Como, Markus Hallermann, Stephan Haneder, and Jochen Feldmann — Photonics and Optoelectronics Group, Department of Physics and CeNS Ludwig-Maximilians-Universität, 80799, Munich (Germany)

Blends of conjugated polymers and fullerene derivatives are one of the most promising systems for organic photovoltaics. We have focussed our attention on the nature of the electronic interactions taking place at the heterojunction between the polymer MDMO-PPV and the fullerene PCBM. The presence of charge transfer excitons in these materials has been recently considered and it appears to have important implications for the solar cell efficiency [1]. Here we demonstrate the presence of hybrid ground- and excited-states at the MDMO-PPV:PCBM heterojunction. Evidence for such states is provided by photoluminescence (PL) spectroscopy, where a red-shifted emission is detected in the blend film, in addition to the MDMO-PPV excitonic emission. A comparison with the spectra of the pristine polymer or PCBM indicates that the new emission originates exclusively from a charge transfer exciton forming between the two materials in the blend. In contrast to exciplexes reported in polymer/polymer blends, the emission at 1.4 eV can be directly excited below the gap of the two materials, demonstrating the presence of a ground state [1].

[1] M. Hallermann, S. Haneder, E. Da Como, Applied Physics Letters 93, 053307 (2008)