Dresden 2009 – wissenschaftliches Programm
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SYOP: Symposium Organic Photovoltaics: From Single Molecules to Devices
SYOP 4: Organic Photovoltaics: from Single Molecules to Devices
SYOP 4.25: Poster
Donnerstag, 26. März 2009, 16:30–19:00, P1A
Energy levels and work function of ultra-thin polythiophene films on conductive polymer electrodes — •Johannes Frisch1, Norbert Koch1, Jürgen P. Rabe1, and Antje Vollmer2 — 1Humboldt-Universität zu Berlin, Institut f. Physik, 12489 Berlin — 2BESSY GmbH, 12489 Berlin
Because poly(ethylenedioxythiophene):poly(styrenesulfonate) (PEDT:PSS) as transparent anode and poly(3-hexylthiophene) (P3HT) as prototypical donor polymer are prototypical materials in modern organic photovoltaic cells (OPVCs), knowledge about the energy levels at interfaces between PEDT:PSS and P3HT is essential to identify the influence of these on the efficiency of OPVCs. In the present work, the morphology, work function, and energy level alignment of ultra-thin films of P3HT on PEDT:PSS was investigated using X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). Ultra-thin films (down to sub-monolayer range) were produced by spin coating P3HT films from chloroform solution on PEDT:PSS and a subsequent washing process. The deposition of such ultra-thin P3HT film on PEDT:PSS lowered the sample work function (Φ) by 0.4 eV due to doping of P3HT film with positive charges from the PEDT:PSS layer. The valence band edge (VBE) was found only 0.1 eV below the Fermi-level. For thicker P3HT films (ca. 10nm), Φ further decreases by 0.2 eV and the VBE was observed 0.2 eV below the Fermi-level. These observations are discussed within existing concepts of local work function fluctuations and energy level bending at the P3HT/PEDT:PSS interface.