A method for direct determination of voltage dependent contact resistance and mobility of an organic field effect transistor

The field effect mobility of charge carrier is extracted from the transfer characteristics of an Organic Field Effect Transistor (OFET). This value does not reflect gate-field-dependence. Various methods for measuring contact resistance exists and gate-field-dependent contact resistance can be extracted from the output characteristics of OFET by the method of Transition Voltage Method (TVM). In this report, a simple and generic analytical framework has been developed to extract gate-field-dependent mobility and contact-resistance simultaneously from the output characteristics of an OFET. This method is applied to the output characteristics of an OFET based on 6,13-Bis(triisopropylsilylethynyl)Pentacene, commonly known as TIPS Pentacene and P3HT. For TIPS Pentacene, the gate-field-dependent mobility values from this method are in the order of 10⁻³ cm² V⁻¹ s⁻¹ and the mobility value from transfer characteristics is in the order of 10⁻² cm² V⁻¹ s⁻¹. Both the methods yielded mobility values in the order of 10⁻² cm² V⁻¹ s⁻¹ in case of P3HT based OFET. The effect of gate field on carrier mobility is discussed for an OFET in general. The extracted values for contact-resistance by the present method (~ a few MΩ) and TVM (a little over 10 MΩ) are also found to differ by one order of magnitude for TIPS Pentacene OFET and are in the same order for P3HT based OFET.