Electronic and Structural Properties of Pentacene at Organic/inorganic Interfaces

Organic/inorganic interfaces play a crucial role in flexible electronic devices such as organic field effect transistors (OFETs), organic light emitting diodes (OLEDs) and organic photovoltaics (OPVs). Charge injection and transport through the interface is not only important in understanding devices, but also a primary challenge in developing and optimizing devices. More flexibility in fabricating and controlling devices can be obtained through modifying inorganic surfaces using functional molecules. Functionalized interfaces can be incorporated into OFETs and probed using current-voltage characteristics. This thesis outlines how organic/inorganic interfaces can be studied electrically in OFETs and demonstrates how this strategy can be utilized to characterize tailored interfaces with nanometer-scaled layers. In this thesis, we studied the interface between organic semiconductors and SiO2 using structural and electrical characterization of pentacene monolayers on SiO2. The dependence of the electrical properties of pentacene on the structure of pentacene islands was studied using atomic force microscopy and in situ electrical measurements during deposition. The mobilities of holes in pentacene monolayers were extracted using fourcontact electrical measurements that probe the pentacene layer independent of the metalpentacene contacts. We studied the electrical properties of rubrene thin films deposited on SiO2 and polystyrene. Rubrene thin film transistors showed very low field effect mobilities on SiO2. Enhanced mobilities on polystyrene were related to the structural properties of rubrene at the interface between rubrene and the gate dielectrics. Both electron and hole conduction