Dresden 2009 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 22: Fokus: Conjugated Polymers
CPP 22.1: Topical Talk
Mittwoch, 25. März 2009, 09:30–10:00, ZEU 160
Charge transport in doped poly(p-phenylene vinylene) — Y. Zhang, B. de Boer, and •P. W. M. Blom — Zernike Institute for Advanced Materials and Dutch Polymer Institute, University of Groningen, The Netherlands
The hole transport in poly(dialkoxy-p-phenylene vinylene) (PPV) based diodes is known to be space-charge limited (SCL) for Ohmic contacts. At room temperature the SCL current in PPV-derivatives is governed by the dependence of the hole mobility on charge carrier density, whereas at low temperatures the field-dependence prevails [1]. We present controlled p-type doping of MEH-PPV deposited from solution using tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) as a dopant. By using a co-solvent aggregation in solution can be prevented and doped films can be deposited. Upon doping the current-voltage characteristics of MEH-PPV based hole-only devices are increased by several orders of magnitude and a clear Ohmic behavior is observed at low bias. Taking the density dependence of the hole mobility into account the free hole concentration due to doping can be derived. We find that a doping concentration of 1.0 wt.% leads to a free carrier density of 2 × 1022 m−3. Neglectance of the density-dependent mobility would lead to an overestimation of the free hole density by an order of magnitude. The free hole densities are further confirmed by impedance measurements on Schottky diodes based on F4-TCNQ doped MEH-PPV and a silver electrode.
1. C. Tanase, P.W.M. Blom, and D.M. de Leeuw, Phys. Rev. B.70, 193202 (2004)