Interface engineering to enhance charge injection and transport in solution-deposited organic transistors

Abstract

Soluble small molecule organic semiconductors combine the high-performance of small molecule organic semiconductors with the versatile processability of polymeric materials, but the control of device performance and uniformity is challenged by the complex film microstructure formed in these materials, and its strong dependence on processing conditions. These films crystallize via a nucleation and growth mechanism that can be difficult to control. In this study we used highly fluorinated self-assembled monolayers (SAMs) to modify the surface of the source and drain contacts and improve the performance of organic thin-film transistors (OTFTs) through controlling film microstructure and lowering the contact resistance. We reached charge carrier mobilities as high as 5.7 cm2/V in 2,8-Difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene (diF-TES ADT), one order of magnitude greater than what we obtained in devices on untreated substrates, and on par with the value reported for single crystal devices. Kelvin probe measurements distinguished an increase in the work function between 0.28 eV and 0.5 eV, depending on the molecular structure of the SAM. Selected area electron diffraction (SAED) confirmed the preferential “edge-on” molecular orientation of the semiconductor. We discuss the device performance in relation to the film morphology and contact resistance.