Berlin 2012 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 13: Focus Session: Structural Ordering and Electronic Transport II (jointly with CPP)
HL 13.8: Talk
Monday, March 26, 2012, 17:15–17:30, ER 270
Origins of low charge mobility in crystalline acceptor-substituted oligothiophenes — Manuel Schrader1, Roland Fitzner2, Moritz Hein3, Chris Elschner3, Bjoern Baumeier1, Moritz Riede3, Karl Leo3, and •Denis Andrienko1 — 1Max Planck Institute for Polymer Research, Mainz, Germany — 2Institute of Organic Chemistry II and Advanced Materials, Ulm, Germany — 3Institute of Applied Photophysics, Dresden, Germany
In a small molecule-based organic solar cell, optical absorption in the visible spectrum, needed for efficient photon harvesting, and the relative donor-acceptor level alignment, required for efficient exciton dissociation, are currently achieved by tuning the electron affinity, the ionization potential, and the band gap of the donor material. In dicyanovinyl-substituted oligothiophenes this is realized by covalently binding an electron-withdrawing group (dicyanovinyl) to an electron-donating core (thiophene oligomer). Such an internal donor-acceptor molecular architecture, however, results in large local molecular dipole moments and thus substantial electrostatic energetic disorder, which leads to pronounced Poole-Frenkel behavior and low charge mobilities, even in a crystalline phase. Analyzing charge transport of dicyanovinyl-substituted oligothiophenes, we propose chemical design rules for the donor which offer a compromise between band gap and charge mobility engineering.