Effect of hydroxyl density on condensation behaviors of self-assembled monolayers and performance of pentacene-base organic thin-film transistors

A series of self-assembled monolayers (SAMs), comprising octadecyltrichlorosilane (ODTS), dodecyltrichlorosilane (DDTS), and hexamethyldisilazane (HMDS), were prepared to examine the effects of phase states and condensation behaviors of SAMs on the morphologies and performance of pentacene-based organic field-effect transistors (OFETs) by means of Fourier Transform Infrared (FT-IR) spectrometer, atomic force microscope (AFM), X-ray diffraction (XRD), and semiconductor parameter analyzer. Experimental results reveal that the treatment of SiO₂ substrates with O₂ plasma (denoted as O₂-SiO₂) and the preparation temperature of SAMs dramatically influence the morphologies of SAMs and the performance of corresponding pentacene-based (no purification) OFETs. When the SAMs were prepared at 30 °C, the OFET based on ODTS-treated O₂-SiO₂ substrate had the highest hole mobility, reaching as large as 1.15 cm² V^?1 s^?1, and an on/off current ratio in excess of 10⁵; these values are both much larger than those of a device based on ODTS-modified SiO₂ substrates without O₂ plasma treatment and O₂-SiO₂ substrates modified by ODTS SAMs prepared at other temperatures. OFETs based on O₂-SiO₂ substrates that were modified by DDTS and HMDS SAMs prepared at 4 °C performed best.