Manipulation of charge carrier injection into organic field-effect transistors by self-assembled monolayers of alkanethiols

Charge carrier injection into two semiconducting polymers is investigated in field-effect transistors using gold source and drain electrodes that are modified by self-assembled monolayers of alkanethiols and perfluorinated alkanethiols. The presence of an interfacial dipole associated with the molecular monolayer at the metal/semiconductor interface changes the work function of the electrodes, and, hence, the injection of the charge carriers. The FET characteristics are analysed with the transfer line method and the hole injection into poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV) and regio-regular poly(3-hexyl)thiophene (rr-P3HT) is investigated. The device parameters are corrected for the contact resistances of the electrodes and the mobilities of the polymers (MEH-PPV, μ_FET = 4 × 10^-4 cm² V^-1 s^-1 and rr-P3HT, μ_FET = (1-2) × 10^-2 cm² V^-1 s^-1) are determined. The contact resistance obtained for the SAM-modified electrodes is at least one order of magnitude larger than for untreated contacts.