Reducing Contact Resistance in Organic Field-Effect Transistors: A Comprehensive Comparison between 2D and Microrod Single Crystals

Abstract

A comprehensive comparison of organic single crystals based on a single material but with different dimensions provides a unique approach to probe their carrier injection mechanism. In this report, both two-dimensional (2D) and microrod single crystals with the same crystalline structure of an identical thiopyran derivative, 7,14-dioctylnaphtho[2,1-f:6,5-f′]bis(cyclopentane-[b]thiopyran) (C 8 -SS), are grown on a glycerol surface with the space-confined method. Organic field-effect transistors (OFETs) based on the 2D C 8 -SS single crystal exhibit superior performance compared with those based on the microrod single crystal, particularly in their contact resistance (R C ). It is demonstrated that the resistance of the crystal bulk in the contact region plays a key role in R C of the OFETs. Thus, among the 30 devices tested, the microrod OFETs typically appear contact-limited, whereas the 2D OFETs possess significantly reduced R C arising from the tiny thickness of the 2D single crystal. The 2D OFETs show high operational stability and high channel mobility up to 5.7 cm 2 /V•s. The elucidation of the contact behavior highlights the merits and great potential of 2D molecular single crystals in organic electronics.