Self-Assembled Monolayers of Phosphonic Acids with Enhanced Surface Energy for High-Performance Solution-Processed N-Channel Organic Thin-Film Transistors

摘要

A self-assembled monolayer (SAM) is only a few nanometers thick, but can dramatically change the surface properties. Herein we report novel SAMs of phosphonic acids (shown in Figure 1 a), which are completely wettable by various organic solvents because of the enhanced surface energy of the SAMs, leading to solution-processed n-channel organic thin-film transistors (OTFTs) with average field effect mobility as high as 1.6cm~2V~(-1)s~(-1). OTFTs are elemental units in organic integrated circuits that, for example, operate radio-frequency identification (RFID) tags and sensors and are used to drive individual pixels in active matrix displays. For these applications, solution-processed OTFTs can be' fabricated onto flexible substrates over a large area at low cost using roll-to-roll or ink-jet printing techniques. OTFTs are interface devices with their performance highly dependent on the interface between organic semiconductors and gate dielectrics no matter whether the organic semiconductors are processed by vacuum deposition or solution-based methods. Owing to the key importance of the semiconductor-dielectric interface, great efforts have been made in interface engineering to control the interface structures, such as molecular ordering, surface dipoles, and film morphology. By virtue of their ability to manipulating the surface properties, SAMs of organosilanes and phosphonic acids have been developed as a very powerful tool to modify the dielectric oxide surface in OTFTs, particularly vacuum-deposited OTFTs. It is worth noting that the success of a specific SAM in vacuum-deposited OTFTs is often barely duplicated in solution-processed OTFTs, and controlling the morphology of solution-processed films of organic semiconductors is usually complex.