The effect of the dielectric end groups on the positive bias stress stability of N2200 organic field effect transistors

Abstract

Bias stress degradation in conjugated polymer field effect transistors is a fundamental problem in disordered materials and can be traced back to interactions of the material with environmental species [H. Sirringhaus, Adv. Mater. 21, 3859–3873 (2009); S. Park et al., Adv. Funct. Mater. 30 1904590-1–1904590-21 (2020); and W. H. Lee et al., Adv. Mater. 26, 1660–1680 (2014)], as well as fabrication-induced defects [H. Klauk, Organic Electronics: Materials, Manufacturing, and Applications (Wiley, 2006) and M. Nikolka et al., Nat. Mater. 16, 356–362 (2017)]. However, the effect of the end groups of the polymer gate dielectric and the associated dipole-induced disorder on bias stress stability has not been studied so far in high-performing n-type materials, such as N2200 [H. Yan et al., Nature 457, 679–686 (2009) and S. Brixi et al., Sci. Rep. 10, 4014 (2020)]. In this work, the performance metrics of N2200 transistors are examined with respect to dielectrics with different end groups [Cytop-M (CTL-809M) and Cytop-S (CTX809-SP2) as purchased from AGC Inc.]. We hypothesize that the polar end groups would lead to increased dipole-induced disorder and worse performance [H. Sirringhaus, Adv. Mater. 21, 3859–3873 (2009); N. B. Ukah et al., J. Polym. Sci., Part B: Polym. Phys. 51, 1533–1542 (2013); and S. Kim et al., Sci. Technol. Adv. Mater. 19, 486–494 (2018)]. The long-time annealing scheme at lower temperatures used in this paper is assumed to lead to better crystallization by allowing the crystalline domains to reorganize in the presence of the solvent [C. S. Kim et al., Appl. Phys. Lett. 93, 103302 (2008)]. It is hypothesized that the higher crystallinity could narrow down the range at which energy carriers are induced and thus decrease the gate dependence of the mobility. The results show that the dielectric end groups do not influence the bias stress stability of N2200 transistors. However, long annealing times result in a dramatic improvement in bias stress stability, with the most stable devices having a mobility that is only weakly dependent on or independent of gate voltage.