Charge Injection in Organic Transistors and its Impact on the Validity of the Extracted Device Parameters

Organic semiconductors have sparked interest given their ease of processing, chemical diversity and tunable optoelectronic properties, which make them viable candidates for incorporation in low-cost, large-area flexible electronics. Nevertheless, transition to market place was not possible because the performance of organic devices has not reached the necessary benchmarks. Inefficient injection of charges from device electrodes into the semiconductor layer represents a significant hurdle in the pursuit of the promised potential of organic semiconductors. In this presentation I will discuss the origin and characterization of contact resistance in organic field-effect transistors (OFETs) and the impact on device performance and accuracy in extraction of charge carrier mobility. I will then present a strategy for reducing contact resistance in small molecule and polymeric OFETs, which consists of developing high work function domains at the surface of the injecting electrodes to promote channels of enhanced injection.1 By using this methodology, we demonstrated high-mobility transistors with near ideal current-voltage characteristics, contact resistances of 200 Ωcm, and device charge carrier mobilities of 20 cm2/Vs, independent of the applied gate voltage. I will further discuss fabrication of all-printed OFETs on conventional paper. For such devices, contacts were deposited using aerosol spray and patterned with a digitally printed mask from an office laser printer, at ambient temperature and pressure, while the organic semiconductor was deposited using an office laser printer.2 The method was successfully adopted for manufacturing different types of OFETs that showed an excellent tolerance to extreme bending, confirming its potential for emerging printed electronics applications.