Trap-Free Charge Transport Approaches in Polymer Thin Film Transistors

Abstract

Polymer-based thin film transistors are being investigated for use in large-area, flexible applications due to their ideal solution processability and low processing costs [1-4]. The performance of these materials has greatly improved over the past two decades with some charge carrier mobilities > 4 cm2/Vs [5-8]. However, charge carrier trapping in these disordered materials is still limiting the charge carrier mobility as shown in numerous polymer thin film transistor studies [9-10]. We will compare the experimental results of several approaches to reduce the density of charge carrier trapping occurring in the polymer thin film and the subsequent improvement in transistor performance. Thin film transistors have been fabricated by blending semiconducting polymers with a wide variety of small organic molecules and then measured to observe any changes in the charge carrier mobility of the polymers. The small molecules are being used to solubilize alkyl chains dangling off the polymer backbone and to improve the ordering of the polymer chains, which reduces the amount of trap states caused by crystalline disorder. The polymer/small molecule blend films have already achieved comparable output characteristics, transfer characteristics, and charge carrier mobilities to those seen in the neat polymer films. The performance can also be tuned based off the polymer concentration with respect to that of the small molecule. We will also present studies on the effects of this blending approach on other key figures of merit for thin film transistors such as threshold voltage, subthreshold swing, on-off current ratio, contact resistance, device stability, and device-to-device variation. [1] Bucella, S. G.; Luzio, A.; Gann, E.; Thomsen, L.; McNeill, C. R.; Pace, G.; Perinot, A.; Chen, Z.; Facchetti, A.; Caironi, M. Nat. Commun. 2015, 6, 1-10. [2] Drury, C. J.; Mutsaers, C. M. J.; Hart, C. M.; Matters, M.; de Leeuw, D. M. Appl. Phys. Lett. 1998, 73(1), 108-110. [3] Fix, W.; Ullmann, A.; Ficker, J.; Clemens, W. Appl. Phys. Lett. 2002, 81(9), 1735-1737. [4] Gelink, G. H.; Huitema, H. E. A.; van Veenendaal, E.; Cantatore, E.; Schrijnemakers, L.; van der Putten, J. B. P. H.; Geuns, T. C. T.; Beenhakkers, M.; Giesbers, J. B.; Huisman, B.-H.; Meijer, E. J.; Benito, E. M.; Touwslager, F. J.; Marsman, A. W.; van Rens, B. J. E.; de Leeuw, D. M. Nat. Mater. 2004, 3(2), 106-110. [5] Bao, Z.; Dodabalapur, A.; Lovinger, A. J. Appl. Phys. Lett. 1996, 69, 4108-4110. [6] Sirringhaus, H.; Wilson, R. J.; Friend, R. H.; Inbasekaran, M.; Wu, W.; Woo, E. P.; Grell, M.; Bradley, D. D. C. Appl. Phys. Lett. 2000, 77, 406-408. [7] Ha, T.-J.; Sonar, P.; Dodabalapur, A. ACS Appl. Mater. Interfaces 2014, 6(5), 3170-3175. [8] Sirringhaus, H. Adv. Mater. 2014, 26, 1319-1335. [9] Venkateshvaran, D.; Nikolka, M.; Sadhanala, A.; Lemaur, V.; Zelazny, M.; Kepa, M.; Hurhangee, M.; Kronemeijer, A. J.; Pecunia, V.; Nasrallah, I.; Romanov, I.; Broch, K.; McCulloch, I.; Emin, D.; Oliview, Y.; Cornil, J.; Beljonne, D.; Sirringhaus, H. Nature 2014, 515, 384-388. [10] Nikola, M.; Nasrallah, I.; Rose, B.; Ravva, M. K.; Broch, K.; Sadhanala, A.; Harkin, D.; Charmet, J.; Hurhangee, M.; Brown, A.; Illig, S.; Too, P.; Jongman, J.; McCulloch, I.; Bredas, J.-L.; Sirringhaus, H. Nat. Mater. 2016, 16, 356-362.