Berlin 2012 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 72: Poster Session: Si-based Photovoltaics / Inorganic Photovoltaics / Structure and Transport in Organic Photovoltaics / Organic Semiconductors

HL 72.24: Poster

Mittwoch, 28. März 2012, 16:00–19:00, Poster D

Optical properties of single crystalline pentacene and perfluoropentacene layers — •Jonatan Helzel, Mathias Schulz, Mira El Helou, Tobias Breuer, Gregor Witte, and Wolfram Heimbrodt — Philipps Universität Marburg department of physics and material sciences centre Germany, Renthof 5, D-35032 Marburg

We prepared pentacene films with thicknesses of 10 nm, 20 nm and 100 nm on different ZnO surfaces by molecular beam deposition under ultra-high vacuum conditions. By varying the growth temperature, we prepared pentacene films in an amorphous phase, in the thin film phase and the Campbell phase. To characterize the films AFM and X-ray diffraction measurements have been done. The pentacene molecules form single crystalline islands with extensions of several µm. So we were able to measure the absorption on single islands and found a polarisation dependence of both Davydov components perpendicularly to each other. The electronic transitions of the pentacene films have been measured in the temperature range between 10 K and room temperature. We observed a thickness dependent shift of the pentacene states upon cooling. At 10 K there is a difference of about 30 meV between the electronic states of a 10 nm and a 100 nm thick pentacene film. The reason for this behaviour is the very different thermal expansion coefficients of substrate and film resulting in a strong in-plane tensile strain. This strain causes little rifts in the film, which leads to a hysteretic temperature shift of the excitons. Analogous measurements have been done on single crystalline perfluoropentacene on KCl and NaF substrates.