Regensburg 2007 – scientific programme
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SYOE: Symposium Organic Thin Film Electronics: From Molecular Contacts to Devices
SYOE 6: Transport in Organics Materials
SYOE 6.2: Talk
Tuesday, March 27, 2007, 15:15–15:30, H32
Trapped-Space-Charge-Limited Currents in Organics — •Gernot Paasch1, Paul Blom2, Magda Mandoc2, and Bert de Boer2 — 1IFW Dresden, Germany — 2University of Groningen, The Netherlands
The Mott-Gurney law for space charge limited current (SCLC) has been modified early [1] to account for the presence of exponentially distributed traps. This expression has been widely used to analyse transport in organic light emitting diodes. However, the theory fails to describe the rather weak temperature dependence observed for electron transport, for instance in PPV derivatives [2]. There we have shown that the trap-limited SCLC law is essentially modified if the density of transport states is of Gaussian type. Here, we discuss the origin of this modification and present a detailed analysis of the modified law. In addition, we derive further modifications for different combinations of densities of states of both the transport states and the trap distribution. As a result, rather different dependencies of the current on voltage, layer thickness and temperature are possible. Consequently, one has to exercise care in order to obtain reliable trap parameters from SCLC.
[1] P. Mark and W. Helfrich, J. Appl. Phys. 33, 205 (1962).
[2] M. M. Mandoc, B. de Boer, G. Paasch, P. W. M. Blom, submitted.