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DS: Fachverband Dünne Schichten
DS 18: Poster: Towards Molecular Spintronics, Organic Thin Films, Optical Layers, Vibrational Spectroscopy, Tayloring organic interfaces
DS 18.13: Poster
Tuesday, February 26, 2008, 14:30–19:30, Poster A
Exciton diffusion length measurements on organic thin films for the application in photovoltaic cells — •Tobias Schuon, Tobias Roller, and Jens Pflaum — 3. Physikalisches Institut, Universität Stuttgart, D-70550 Stuttgart
The exciton diffusion length, LD, has an important impact on the efficiency of photovoltaic devices. Therefore the detailed knowledge of the dependence of this quantity on the structural and chemical sample properties is crucial for PV cell optimization. In this work LD has been measured by photoluminescence quenching on layers of various materials, viz. DIP (diindenoperylene), CuPc and PTCBI, and at different thicknesses. Alternatively, we estimated LD via the spectral PV photocurrent on the basis of a suited exciton diffusion model1. To achieve a complete set of material and device parameters, comprehensive studies by X-ray diffraction, UV-Vis spectroscopy and AFM have been performed.
As a key result, DIP provides an exciton diffusion length in the order of 100 nm, thereby compensating for its rather weak absorption2. We related this high LD to the fact, that DIP forms a structural phase of high crystallinity on weakly interacting substrates, with its long molecular axis preferentially oriented along the surface normal3. Furthermore, balanced electron and hole mobilities along this crystallographic direction support the application of DIP in PV devices4.
[1] A.K.Ghosh, T.Feng, J.Appl.Phys. 49, 5982 [2] D.Kurrle, J.Pflaum, Appl.Phys.Lett. (subm.) [3] A.C.Dürr, et al., Appl.Phys.Lett. 81, 2276 [4] A.K.Tripathi, J.Pflaum, Appl.Phys.Lett. 89, 82103