Tuning contact resistance in top-contact p-type and n-type organic field effect transistors by self-generated interlayers

Contact resistance significantly limits the performance of organic field-effect transistors (OFETs). Positioning interlayers at the metal/organic interface can tune the effective work-function and reduce contact resistance. Myriad techniques offer interlayer processing onto the metal pads in bottom-contact OFETs. However, most methods are not suitable for deposition on organic films and incompatible with top-contact OFET architectures. Here, a simple and versatile methodology is demonstrated for interlayer processing in both p- and n-type devices that is also suitable for top-contact OFETs. In this approach, judiciously selected interlayer molecules are co-deposited as additives in the semiconducting polymer active layer. During top contact deposition, the additive molecules migrate from within the bulk film to the organic/metal interface due to additive-metal interactions. Migration continues until a thin continuous interlayer is completed. Formation of the interlayer is confirmed by X-ray photoelectron spectroscopy (XPS) and cross-section scanning transmission electron microscopy (STEM), and its effect on contact resistance by device measurements and transfer line method (TLM) analysis. It is shown that self-generated interlayers that reduce contact resistance in p-type devices, increase that of n-type devices, and vice versa, confirming the role of additives as interlayer materials that modulate the effective work-function of the organic/metal interface.