Dresden 2011 – scientific programme

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DS: Fachverband Dünne Schichten

DS 42: Poster I: Progress in Micro- and Nanopatterning: Techniques and Applications (jointly with O); Spins in Organic Materials; Ion Interactions with Nano Scale Materials; Organic Electronics and Photovoltaics; Plasmonics and Nanophotonics (jointly with HL and O); High-k and Low-k Dielectrics (jointly with DF); Organic Thin Films; Nanoengineered Thin Films; Layer Deposition Processes; Layer Properties: Electrical, Optical, and Mechanical Properties; Thin Film Characterisation: Structure Analysis and Composition; Application of Thin Films

DS 42.36: Poster

Wednesday, March 16, 2011, 15:00–17:30, P1

Photoelectron Spectroscopy Investigation of the C60/Calcium Interface — •Holger Wetzstein¹, Darius Bunandar², Julia Schafferhans³, Carsten Deibel³, Achim Schöll¹, and Friedrich Reinert¹ — ¹Experimental Physics VII, Julius-Maximilians-University of Würzburg, D-97074 Würzburg — ²Department of Physics, University of Texas at Austin, Austin, Tx 78712-0264 — ³Experimental Physics VI, Julius-Maximilians-University of Würzburg, D-97074 Würzburg

Device lifetime is a crucial point for organic solar cells. Therefore it is important to understand the degradation mechanisms as well as their consequence on the performance of these photovoltaic devices. We observed a characteristic S-shape in the I/V-curves of P3HT/PCBM-bulk heterojunction cells with calcium contacts. A tentative origin of this behavior is a reaction of the calcium with oxygen, which leads to alterations in the regime of the anode interface. To shed more light on this issue we investigated the electronic structure of the Ca/C60 interface, which serves as a model for the PCBM/Ca contact. X-ray (XPS) and ultra-violet photoelectron spectroscopy (UPS) measurements were performed on C60 layers adsorbed on epitaxially grown Calcium as well as on Ca deposited on C60. In both cases, the data clearly show the formation of an interface state due to the charge transfer from the Ca into the C60, which is an indication for a chemical reaction. Moreover, we studied the effect of oxygen exposure on the interfacial chemical and electronic structure under conditions comparable to the conditions during device operation.