Berlin 2012 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 58: Focus Session: Structure and Transport in Organic Photovoltaics III (jointly with CPP)

HL 58.6: Talk

Wednesday, March 28, 2012, 16:15–16:30, ER 270

Equivalent circuit analysis for understanding s-shaped IV-characteristics in organic solar cells — •Bernhard Ecker¹, Hans-Joachim Egelhaaf², Roland Steim², Jürgen Parisi¹, and Elizabeth von Hauff^3,4 — ¹Energy and Semiconductor Research Laboratory, Institute of Physics, Carl von Ossietzky University, 26111 Oldenburg, Germany — ²Konarka Technology GmbH, Landgrabenstr. 94, Nürnberg, Germany — ³Institute of Physics, Albert-Ludwigs University of Freiburg, 79104 Freiburg, Germany — ⁴Fraunhofer Institute for Solar Energy Systems, Heidenhofstr. 2, 79110 Freiburg, Germany

In this contribution we investigate the origin of s-shaped current voltage (IV) characteristics in inverted solar cells with a TiOx interlayer between the cathode and the P3HT:PCBM active layer. Initially, the solar cells demonstrate s-shaped IV characteristics, resulting in a low fill factor (FF). Upon light soaking with UV radiation the resistivity of the TiOx interlayer decreases, the s-shape disappears and the FF increases. Impedance spectroscopy (IS) is used to investigate the influence of the resistivity of the TiOx layer on the shape of the IV characteristics. A simple equivalent circuit is proposed to model the experimental data in both conditions, i.e. with s-shaped and regular shaped IV characteristics, respectively. The equivalent circuit elements can be attributed to the distinct layers in the solar cell, therefore giving insight into the origin of the s-shape. We show that IS in conjunction with equivalent circuit analysis can provide detailed information and we identify the resistivity of the TiOx interlayer ultimately influencing the shape of the IV characteristics.