| AVS 54th International Symposium | |
| Electronic Materials and Processing | Monday Sessions |
| Session EM-MoM |
| Session: | Organic Materials and Devices |
| Presenter: | K.A. Singh, Carnegie Mellon University |
| Authors: | K.A. Singh, Carnegie Mellon University G. Sauve, Carnegie Mellon University R. Zhang, Carnegie Mellon University R.D. McCullough, Carnegie Mellon University L.M. Porter, Carnegie Mellon University |
| Correspondent: | Click to Email |
In this study we report on the interdependence of morphology, mobility, and contact resistance in field effect-transistors (FETs) based on poly(3-hexyl thiophene) (P3HT) as the active layer. Bottom-contact FETs with Pt electrodes were fabricated with channel lengths varying from 3 to 40µm.The P3HT films were deposited using a solvent-assisted drop casting technique. Atomic force microscopy images indicate that P3HT self assembles into a lamellar structure consisting of nanorods, which contribute to high field-effect mobilities. Our AFM images, along with prior X-ray data,1 show that an increase in the molecular weight of the polymer leads to an increase in the size of the self-assembled nanorods, leading to higher crystallinity of the polymer. Our results show that both the mobility and the contact resistance depend strongly on the molecular weight, or morphology, of the polymer. For example, at a gate voltage of -80V, the mobility increased from 0.03 to 0.16cm2V-1s-1 and the contact resistance decreased from 2.2 to 0.4MΩ when the molecular weight was increased from 5.5 to 11Kg mol-1. These mobility values were obtained after correcting for the contact resistance. The results also show a dependence of the mobility and the contact resistance on the gate voltage: The contact resistance decreased from 1.2 to 0.4MΩ with an increase in gate voltage from -20 to -80V; the mobility correspondingly increased by a factor of 8. The dependence of the mobility on the gate voltage is attributed to the presence of traps that limit the charge transport. The effect of mobility on contact resistance can be explained by a diffusion-limited charge injection theory.2 In summary, our results expand on prior individual studies, primarily on Au/P3HT, that indicate a correlation between mobility and either the contact resistance3 or molecular weight1, to a systematic study on Pt/P3HT transistors. Future experiments with higher molecular-weight P3HT are also planned for comparison.
1 R. Zhang, B. Li, M.C. Iovu, M. Jeffries-EL, G. Sauve, J. Cooper, S. Jia, S. Tristram-Nagle, D.M. Smilgies, D.N. Lambeth, R.D. McCullough, and T. Kowalewski, J. Am. Chem. Soc. 128[11], 3480(2006)
2 V. I. Arkhipov, E. V. Emelianova, Y. H. Tak, and H. Bassler, J. Appl. Phys. 84[2], 848(1998)
3 B. H. Hamadini and D. Natelson, Appl. Phys. Lett. 84[3], 443(2004).