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In this study, the conducting channel in poly(3-hexylthiophene) (P3HT) organic field effect transistors (OFETs) was investigated. The effect of varying the P3HT layer thickness on the OFET parameters was studied. The threshold voltage and the field effect mobility were determined from both the linear and saturation regime of the OFET output characteristics for all film thicknesses and the results are compared and discussed. A gated four probe technique was used to investigate the formation and evolution of the conducting channel by monitoring changes in potential at different points in the channel during measurement. It was found that the device performance of the OFETs was significantly influenced by the thickness of the P3HT layer. Bulk currents were found to dominate device performance for thicker P3HT layers. [ABSTRACT FROM AUTHOR]

The hole mobility of a semiconducting film with a new type of small molecule has been determined by electrical characterization with two different device geometries. The small molecule, namely Zn(OC)2, consists of oxadiazole groups (O), that act as electron conductor and blue emitter, and carbazole groups (C), that are hole conductors, which are arranged around a central Zn-atom. This disordered organic material has in principal ambipolar conduction properties. In both the organic devices investigated, that is, a vertical diode and a bottom-gate organic field effect transistor, the transport is dominated by holes. In the diode structure, the charge carrier transport shows a dependence from the electric field with a space charge limited current characteristic. The hole mobility value is several orders of magnitude higher as compared to the one extracted from the characteristics of the organic transistor. This large difference in the charge carrier transport properties for the two different device configurations is due to the strong influence of the dielectric/semiconductor interface which degrades the hole transport in the organic field effect transistor. [ABSTRACT FROM AUTHOR]