Regensburg 2007 – wissenschaftliches Programm

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DS: Fachverband Dünne Schichten

DS 6: Organic Photovoltaics (SYOE 2)

DS 6.1: Vortrag

Montag, 26. März 2007, 16:00–16:15, H32

Exciton Diffusion length Measurements in Diindenoperylene Thin Films — •Tobias Roller, Dieter Kurrle, Philipp Neumann, and Jens Pflaum — 3. Physikalisches Institut, Universität Stuttgart

To accomplish large exciton diffusion lengths is a major task for the successful implementation of molecular thin films in organic photovoltaic cells. The exciton diffusion length determines the maximal useful thickness of the absorbing layer in excitonic photovoltaic (PV) cells, thus governing their internal quantum efficiency.

To analyse the exciton diffusion length in relation to the structural properties we have studied thin films of the organic semiconductor Diindenoperylene (DIP) prepared by MBE in HV at thicknesses up to 400nm. Due to its tapered ends this molecule provides long-range order in the direction normal to the surface of weakly-interacting substrates such as ITO. By XRD we were able to access the structural film parameters along the exciton diffusion path, namely their out-of-plane lattice spacing, crystallite size and average tilting angle. The exciton diffusion lengths were estimated from the spectral photocurrent of DIP PV-cells and, additionally, measured by quenched photoluminescence of Palladium Phthalocyanine capped DIP layers. The observed diffusion length in DIP exceeds 100nm for the thickest films and shows a direct correlation with the crystallite sizes along the surface normal. We will discuss these results and possible mechanisms of exciton trapping and annihilation with respect to the film structure of DIP.

Financial support by the DFG (PF385/2-3) and BASF is acknowledged.