Effects of source/drain electrode contact length on the photoresponsive properties of organic field-effect transistors

Abstract

With the continual increase of the carrier mobility of organic semiconductors, there is a great need for optimizing the contact between source/drain electrode and organics in order to further improve the performance of organic field-effect transistors. The effects of Au source/drain electrode contact length on the photosensitivity in pentacene-based organic field-effect transistors were systematically investigated. The results show that at a given gate voltage and drain voltage, the drain current increases with the contact length at first and then tends to saturate at a contact length of 0.7 mm. It is observed that the effective mobility under illumination, both in the linear region and the saturation region, as well as the photoresponsivity and the external quantum efficiency, increase with contact length. All of these can be attributed to the reduction of contact resistance with the increase of contact length. Moreover, analytical expressions were derived and successfully describe the measured dependence of the drain current on the contact length.