Self-assembled monolayers (
SAMs) of organic molecules are frequently employed to improve the electrical performance of organic field-effect transistors (OFETs). However, the relationship between SAM properties and OFET performance has not been fully explored, leading to an incomplete understanding of the system. This study investigates the effect of the SAM alkyl chain length on the crystalline phase of
pentacene films and OFET performance. Two types of
SAMs-with alkyl chain lengths of 10 (decyltrichlorosilane, DTS) and 22 (docosyltrichlorosilane, DCTS)-were examined, and variations in the performance of
pentacene-based OFETs with the nature of the SAM treatment were observed. Despite the similar surface morphologies of the
pentacene films, field-effect mobility in the DCTS-treated OFET was twice that in the DTS-treated OFET. To find the reason underlying the dependence of the OFET's electrical performance on the SAM alkyl chain length, X-ray diffraction measurements were conducted, followed by a phase analysis of the
pentacene films. Bulk and thin-film phases were observed to coexist in the
pentacene film grown on DTS, indicating several structural defects in the film; this can help explain the dependence of the OFET electrical performance on the SAM alkyl chain length, mediated by the different crystalline phases of
pentacene.