AVS 56th International Symposium & Exhibition
    Electronic Materials and Processing Wednesday Sessions
       Session EM-WeM

Paper EM-WeM6
Modulation of Charge Injection and Transport in Poly(3-hexylthiophene)-Based Field-Effect Transistors by Self-Assembled Monolayers

Wednesday, November 11, 2009, 9:40 am, Room B1

Session: Organic & Molecular Electronics
Presenter: K.A. Singh, Carnegie Mellon University
Authors: K.A. Singh, Carnegie Mellon University
T. Nelson, Carnegie Mellon University
J. Belot, Carnegie Mellon University
R.D. McCullough, Carnegie Mellon University
T. Young, Carnegie Mellon University
T. Kowalewski, Carnegie Mellon University
P. Nachimuthu, Pacific Northwest National Laboratory
S. Thevuthasan, Pacific Northwest National Laboratory
L.M. Porter, Carnegie Mellon University
Correspondent: Click to Email
Charge injection and transport in bottom-contact poly(3-hexylthiophene) (P3HT) based field-effect transistors (FETs), wherein the Au source and drain contacts are modified by self-assembled monolayers (SAMs), is reported. Four SAMs of different chemical composition were selected to either enhance or reduce charge injection across the contacts. The rr-P3HT films were drop cast from a solution in chloroform in a saturated environment. Prior to P3HT deposition the FETs were treated with octyltrichlorosilane (OTS) solution in hexadecane for 2 hrs, dried and then immersed in a solution containing one of the SAMs in ethanol for another 2 hrs. The contact resistance (RC) was measured using the transmission line method and the effective field-effect mobility (µ) was determined from the linear region of the transistor characteristics. Treatment of FETs with the first two SAMs resulted in an increase in µ and a decrease in RC, whereas treatment with the other two SAMs resulted in a decrease in µ and an increase in RC. For example, in one case, µ increased from 0.15 to 0.20 cm2V-1s-1 and RC decreased from 0.61 to 0.34 MΩ; in the opposite case, µ decreased to 0.09 cm2V-1s-1 and RC increased to 0.90 MΩ. The electrical properties of the transistors correlate with changes in the metal workfunction by up to 0.9 eV, as estimated using ultraviolet photoelectron spectroscopy. Besides using the SAMs for tuning the charge injection, the monolayer formed by OTS on SiO2 at the insulator/ P3HT interface resulted in improved morphology of the P3HT film, as observed by atomic force microscopy, and an associated increase of µ from 0.03 to 0.15 cm2V-1s-1. In summary, the charge carrier injection and transport in P3HT-based FETs were successfully modulated by treatment with SAMs. The use of OTS at the SiO2/P3HT interface also resulted in improved morphology and enhanced charge transport. Further details regarding the use of self-assembled monolayers will be presented along with the device and photoemission characteristics.