Regensburg 2010 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 40: [CPP] Organic Electronics and Photovoltaics II (Joint Session DS/CPP/HL/O)

O 40.10: Vortrag

Dienstag, 23. März 2010, 16:00–16:15, H37

Energetics of Excited States in the Conjugated Polymer Poly(3-hexylthiophene) — Julien Gorenflot¹, •Daniel Mack¹, Daniel Rauh⁴, Stefan Krause², Carsten Deibel¹, Achim Schöll², Friedrich Reinert^2,3, and Vladimir Dyakonov^1,4 — ¹Experimental Physics VI, University of Würzburg, D-97074 Würzburg — ²Experimental Physics II, University of Würzburg, D-97074 Würzburg — ³FZK Karlsruhe, Gemeinschaftslabor für Nanoanalytik, D-76021 Karlsruhe — ⁴Bavarian Centre for Applied Energy Research (ZAE Bayern), D-97074 Würzburg

Although prototypes and first commercial polymer-based solar panels already exist, a comprehensive understanding of the fundamental processes and energetics involved in photocurrent generation is still missing and limits further device optimisations. We present a complementary set of experiments on poly(3-hexylthiophene(P3HT), which enables us to draw general conclusions on the energy levels and barriers involved in the processes from light absorption to polaron pair dissociation. From photoemission spectroscopy of occupied and unoccupied states we determine the transport gap to 2.6 eV, which we show to be in agreement with the onset of photoconductivity by spectrally resolved photocurrent measurements. We also find that photogenerated singlet excitons, generated with light at the absorption edge, require 0.7 eV of excess energy to overcome the binding energy. The intermediate charge transfer state, also called polaron pair, is situated only 0.3 eV above the singlet exciton. We discuss our results in view of their impact on charge generation.