  Bias stress degradation in conjugated polymer field-effect transistors is a
fundamental problem in these disordered materials and can be traced back to
interactions of the material with environmental species,1,2,3 as well as
fabrication-induced defects.4,5 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 N2200.6,7 In this work, the performance metrics of N2200
transistors are examined with respect to dielectrics with different end groups
(Cytop-M and Cytop-S8). We hypothesize that the polar end groups would lead to
increased dipole-induced disorder, and worse performance.1,9,10 The long-time
annealing scheme at lower temperatures used in the paper is assumed to lead to
better crystallization by allowing the crystalline domains to reorganize in the
presence of the solvent.11 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.
